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L_0764 | using electromagnetism | T_3902 | Figure 25.7 shows a diagram of a simple doorbell. Like most doorbells, it has a button located by the front door. Pressing the button causes two electric contacts to come together and complete an electric circuit. In other words, the button is a switch. The circuit is also connected to a voltage source, an electromagnet, and the clapper of a bell. When current flows through the circuit, the electromagnet turns on, and its magnetic field attracts the clapper. This causes the clapper to hit the bell, making it ring. Because the clapper is part of the circuit, when it moves to strike the bell, it breaks the circuit. Without current flowing through the circuit, the electromagnet turns off. The clapper returns to its original position, which closes the circuit again and turns the electromagnet back on. The electromagnet again attracts the clapper, which hits the bell once more. This sequence of events keeps repeating as long as the button by the front door is being pressed. | text | null |
L_0764 | using electromagnetism | T_3903 | An electric motor is a device that uses an electromagnet to change electrical energy to kinetic energy. Figure 25.8 shows a simple diagram of an electric motor. The motor contains an electromagnet that is connected to a shaft. When current flows through the motor, the electromagnet turns, causing the shaft to turn as well. The rotating shaft moves other parts of the device. Why does the motors electromagnet turn? Notice that the electromagnet is located between the north and south poles of two permanent magnets. When current flows through the electromagnet, it becomes magnetized, and its poles are repelled by the like poles of the permanent magnets. This causes the electromagnet to turn toward the unlike poles of the permanent magnets. A device called a commutator then changes the direction of the current so the poles of the electromagnet are reversed. The reversed poles are once again repelled by the like poles of the permanent magnets. This causes the electromagnet to continue to turn. These events keep repeating, so the electromagnet rotates continuously. You can make a very simple electric motor with a battery, wire, and magnet following instructions at this URL: . | text | null |
L_0765 | generating and using electricity | T_3904 | Just about a decade after Oersted discovered that electric current produces a magnetic field, an English scientist named Michael Faraday discovered that the reverse is also true. A magnetic field produces an electric current, as long as the magnetic field is changing. This is called Faradays law. | text | null |
L_0765 | generating and using electricity | T_3905 | The process of generating electric current with a changing magnetic field is called electromagnetic induction. It occurs whenever a magnetic field and an electric conductor, such as a coil of wire, move relative to one another. As long as the conductor is part of a closed circuit, current will flow through it whenever it crosses magnetic field lines. One way this can happen is pictured in Figure 25.9. It shows a magnet moving inside a wire coil. Another way is for the coil to move instead of the magnet. You can watch an animated version of Figure 25.9 at this URL: http://jsticca.wordpress.com/2009/09/01/the-magn | text | null |
L_0765 | generating and using electricity | T_3906 | The device in the circuit in Figure 25.9 is an ammeter. It measures the current that flows through the wire. The faster the magnet or coil moves, the greater the amount of current that is produced. If more turns were added to the coil, this would increase the strength of the magnetic field as well. If the magnet were moved back and forth repeatedly, the current would keep changing direction. In other words, alternating current would be produced. This is illustrated in Figure 25.10. | text | null |
L_0765 | generating and using electricity | T_3907 | Two important devices depend on electromagnetic induction: electric generators and electric transformers. Both devices play critical roles in producing and regulating the electric current we depend on in our daily lives. | text | null |
L_0765 | generating and using electricity | T_3908 | An electric generator is a device that changes kinetic energy to electrical energy through electromagnetic induction. A simple diagram of an electric generator is shown in Figure 25.11. In a generator, some form of energy is applied to turn a shaft. This causes a coil of wire to rotate between opposite poles of a magnet. Because the coil is rotating in a magnetic field, electric current is generated in the wire. If the diagram in Figure 25.11 looks familiar to you, thats because a generator is an electric motor in reverse. Look back at the electric motor in Figure 25.8. If you were to mechanically turn the shaft of the motor (instead of using electromagnetism to turn it), the motor would generate electricity just like an electric generator. You can learn how to make a very simple electric generator by watching the video at the URL below. Making your own generator will help you understand how a generator works. Generators may be set up to produce either alternating or direct current. Generators in cars and most power plants produce alternating current. A car generator produces electricity with some of the kinetic energy of the turning crankshaft. The electricity is used to run the cars lights, power windows, radio, and other electric devices. Some of the electricity is stored in the cars battery to provide electrical energy when the car isnt running. A power plant generator produces electricity with the kinetic energy of a turning turbine. The energy to turn the turbine may come from burning fuel, falling water, or some other energy source. You can see how falling water is used to generate electricity in Figure 25.12 and in the video at this URL: | text | null |
L_0765 | generating and using electricity | T_3908 | An electric generator is a device that changes kinetic energy to electrical energy through electromagnetic induction. A simple diagram of an electric generator is shown in Figure 25.11. In a generator, some form of energy is applied to turn a shaft. This causes a coil of wire to rotate between opposite poles of a magnet. Because the coil is rotating in a magnetic field, electric current is generated in the wire. If the diagram in Figure 25.11 looks familiar to you, thats because a generator is an electric motor in reverse. Look back at the electric motor in Figure 25.8. If you were to mechanically turn the shaft of the motor (instead of using electromagnetism to turn it), the motor would generate electricity just like an electric generator. You can learn how to make a very simple electric generator by watching the video at the URL below. Making your own generator will help you understand how a generator works. Generators may be set up to produce either alternating or direct current. Generators in cars and most power plants produce alternating current. A car generator produces electricity with some of the kinetic energy of the turning crankshaft. The electricity is used to run the cars lights, power windows, radio, and other electric devices. Some of the electricity is stored in the cars battery to provide electrical energy when the car isnt running. A power plant generator produces electricity with the kinetic energy of a turning turbine. The energy to turn the turbine may come from burning fuel, falling water, or some other energy source. You can see how falling water is used to generate electricity in Figure 25.12 and in the video at this URL: | text | null |
L_0765 | generating and using electricity | T_3909 | An electric transformer is a device that uses electromagnetic induction to change the voltage of electric current. A transformer may either increase or decrease voltage, but it only works with alternating current. You can see the components of an electric transformer in Figure 25.13. As you can see in Figure 25.13, a transformer consists of two wire coils wrapped around an iron core. When alternating primary current passes through coil P, it magnetizes the iron core. Because the current is alternating, the magnetic field of the iron core keeps reversing. This changing magnetic field induces alternating current in coil S, which is part of another circuit. In Figure 25.13, coil P and coil S have the same number of turns of wire. In this case, the voltages of the primary and secondary currents are the same. However, when the two coils have different numbers of turns, the voltage of the secondary current is different than the voltage of the primary current. Both cases are illustrated in Figure 25.14. When coil S has more turns of wire than coil P, the voltage in the secondary current is greater than the voltage in the primary current. This type of transformer is called a step-up transformer. When coil S has fewer turns of wire than coil P, the voltage in the secondary current is less than the voltage in the primary current. This type of transformer is called a step-down transformer. For an animation of a transformer, go to this URL: . | text | null |
L_0765 | generating and using electricity | T_3910 | Power plant generators produce high-voltage electric current. Many power plants also use step-up transformers to increase the voltage of the current even more (see Figure 25.15). By increasing the voltage, the amount of current is decreased, so less power is lost as the electricity travels through the power lines. However, the voltage in power lines is too high to be safe for home circuits. The voltage in power lines may be as great as 750,000 volts, whereas most home circuits are 240 or 120 volts. One or more step-down transformers decrease the voltage of current before it enters the home. Other step-down transformers within the home lower the voltage of some of the homes circuits. For an overview of electric power generation, transmission, and distribution in the U.S., go to this URL: http://w | text | null |
L_0765 | generating and using electricity | T_3910 | Power plant generators produce high-voltage electric current. Many power plants also use step-up transformers to increase the voltage of the current even more (see Figure 25.15). By increasing the voltage, the amount of current is decreased, so less power is lost as the electricity travels through the power lines. However, the voltage in power lines is too high to be safe for home circuits. The voltage in power lines may be as great as 750,000 volts, whereas most home circuits are 240 or 120 volts. One or more step-down transformers decrease the voltage of current before it enters the home. Other step-down transformers within the home lower the voltage of some of the homes circuits. For an overview of electric power generation, transmission, and distribution in the U.S., go to this URL: http://w | text | null |
L_0766 | properties of matter | T_3911 | Both you and the speck of dust consist of atoms of matter. So does the ground beneath your feet. In fact, everything you can see and touch is made of matter. The only things that arent matter are forms of energy, such as light and sound. Although forms of energy are not matter, the air and other substances they travel through are. So what is matter? Matter is defined as anything that has mass and volume. | text | null |
L_0766 | properties of matter | T_3912 | Mass is the amount of matter in a substance or object. Mass is commonly measured with a balance. A simple mechanical balance is shown in Figure 3.1. It allows an object to be matched with other objects of known mass. SI units for mass are the kilogram, but for smaller masses grams are often used instead. | text | null |
L_0766 | properties of matter | T_3913 | The more matter an object contains, generally the more it weighs. However, weight is not the same thing as mass. Weight is a measure of the force of gravity pulling on an object. It is measured with a scale, like the kitchen- scale in Figure 3.2. The scale detects how forcefully objects in the pan are being pulled downward by the force of gravity. The SI unit for weight is the newton (N). The common English unit is the pound (lb). With Earths gravity, a mass of 1 kg has a weight of 9.8 N (2.2 lb). Problem Solving Problem: At Earths gravity, what is the weight in newtons of an object with a mass of 10 kg? Solution: At Earths gravity, 1 kg has a weight of 9.8 N. Therefore, 10 kg has a weight of (10 9.8 N) = 98 N. You Try It! Problem: If you have a mass of 50 kg on Earth, what is your weight in newtons? An object with more mass is pulled by gravity with greater force, so mass and weight are closely related. However, the weight of an object can change if the force of gravity changes, even while the mass of the object remains constant. Look at the photo of astronaut Edwin E. Aldrin Jr taken by fellow astronaut Neil Armstrong, the first human to walk on the moon, in Figure 3.3. An astronaut weighed less on the moon than he did on Earth because the moons gravity is weaker than Earths. The astronauts mass, on the other hand, did not change. He still contained the same amount of matter on the moon as he did on Earth. The amount of space matter takes up is its volume. How the volume of matter is measured depends on its state. The volume of liquids is measured with measuring containers. In the kitchen, liquid volume is usually measured with measuring cups or spoons. In the lab, liquid volume is measured with containers such as graduated cylinders. Units in the metric system for liquid volume include liters (L) and milliliters (mL). The volume of gases depends on the volume of their container. Thats because gases expand to fill whatever space is available to them. For example, as you drink water from a bottle, air rushes in to take the place of the water. An "empty" liter bottle actually holds a liter of air. How could you find the volume of air in an "empty" room? The volume of regularly shaped solids can be calculated from their dimensions. For example, the volume of a rectangular solid is the product of its length, width, and height (l w h). For solids that have irregular shapes, the displacement method is used to measure volume. You can see how it works in Figure 3.4 and in the video below. The SI unit for solid volumes is cubic meters (m3 ). However, cubic centimeters (cm3 ) are often used for smaller volume measurements. | text | null |
L_0766 | properties of matter | T_3913 | The more matter an object contains, generally the more it weighs. However, weight is not the same thing as mass. Weight is a measure of the force of gravity pulling on an object. It is measured with a scale, like the kitchen- scale in Figure 3.2. The scale detects how forcefully objects in the pan are being pulled downward by the force of gravity. The SI unit for weight is the newton (N). The common English unit is the pound (lb). With Earths gravity, a mass of 1 kg has a weight of 9.8 N (2.2 lb). Problem Solving Problem: At Earths gravity, what is the weight in newtons of an object with a mass of 10 kg? Solution: At Earths gravity, 1 kg has a weight of 9.8 N. Therefore, 10 kg has a weight of (10 9.8 N) = 98 N. You Try It! Problem: If you have a mass of 50 kg on Earth, what is your weight in newtons? An object with more mass is pulled by gravity with greater force, so mass and weight are closely related. However, the weight of an object can change if the force of gravity changes, even while the mass of the object remains constant. Look at the photo of astronaut Edwin E. Aldrin Jr taken by fellow astronaut Neil Armstrong, the first human to walk on the moon, in Figure 3.3. An astronaut weighed less on the moon than he did on Earth because the moons gravity is weaker than Earths. The astronauts mass, on the other hand, did not change. He still contained the same amount of matter on the moon as he did on Earth. The amount of space matter takes up is its volume. How the volume of matter is measured depends on its state. The volume of liquids is measured with measuring containers. In the kitchen, liquid volume is usually measured with measuring cups or spoons. In the lab, liquid volume is measured with containers such as graduated cylinders. Units in the metric system for liquid volume include liters (L) and milliliters (mL). The volume of gases depends on the volume of their container. Thats because gases expand to fill whatever space is available to them. For example, as you drink water from a bottle, air rushes in to take the place of the water. An "empty" liter bottle actually holds a liter of air. How could you find the volume of air in an "empty" room? The volume of regularly shaped solids can be calculated from their dimensions. For example, the volume of a rectangular solid is the product of its length, width, and height (l w h). For solids that have irregular shapes, the displacement method is used to measure volume. You can see how it works in Figure 3.4 and in the video below. The SI unit for solid volumes is cubic meters (m3 ). However, cubic centimeters (cm3 ) are often used for smaller volume measurements. | text | null |
L_0766 | properties of matter | T_3914 | Matter has many properties. Some are physical properties. Physical properties of matter are properties that can be measured or observed without matter changing to a different substance. For example, whether a given substance normally exists as a solid, liquid, or gas is a physical property. Consider water. It is a liquid at room temperature, but if it freezes and changes to ice, it is still water. Generally, physical properties are things you can see, hear, smell, or feel with your senses. | text | null |
L_0766 | properties of matter | T_3915 | Physical properties include the state of matter and its color and odor. For example, oxygen is a colorless, odorless gas. Chlorine is a greenish gas with a strong, sharp odor. Other physical properties include hardness, freezing and boiling points, the ability to dissolve in other substances, and the ability to conduct heat or electricity. These properties are demonstrated in Figure 3.5. Can you think of other physical properties? | text | null |
L_0766 | properties of matter | T_3916 | Density is an important physical property of matter. It reflects how closely packed the particles of matter are. Density is calculated from the amount of mass in a given volume of matter, using the formula: Density (D) = Mass (M) Volume (V ) Problem Solving Problem: What is the density of a substance that has a mass of 20 g and a volume of 10 mL? Solution: D = 20 g/10 mL = 2.0 g/mL You Try It! Problem: An object has a mass of 180 kg and a volume of 90 m3 . What is its density? To better understand density, think about a bowling ball and a volleyball. The bowling ball feels heavy. It is solid all the way through. It contains a lot of tightly packed particles of matter. In contrast, the volleyball feels light. It is full of air. It contains fewer, more widely spaced particles of matter. Both balls have about the same volume, but the bowling ball has a much greater mass. Its matter is denser. | text | null |
L_0766 | properties of matter | T_3917 | It looks like frozen smoke, and its the lightest solid material on the planet. Aerogel insulates space suits, makes tennis rackets stronger and could be used one day to clean up oil spills. Lawrence Livermore National Laboratory scientist Alex Gash shows us some remarkable properties of this truly unique substance. For more information on aerogel, see http://science.kqed.org/quest/video/quest-lab-aerogel/ . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0766 | properties of matter | T_3918 | Some properties of matter can be measured or observed only when matter undergoes a change to become an entirely different substance. These properties are called chemical properties. They include flammability and reactivity. | text | null |
L_0766 | properties of matter | T_3919 | Flammability is the ability of matter to burn. Wood is flammable; iron is not. When wood burns, it changes to ashes, carbon dioxide, water vapor, and other gases. After burning, it is no longer wood. | text | null |
L_0766 | properties of matter | T_3920 | Reactivity is the ability of matter to combine chemically with other substances. For example, iron is highly reactive with oxygen. When it combines with oxygen, it forms the reddish powder called rust (see Figure 3.6). Rust is not iron but an entirely different substance that consists of both iron and oxygen. | text | null |
L_0768 | changes in matter | T_3932 | A physical change in matter is a change in one or more of matters physical properties. Glass breaking is just one example of a physical change. Some other examples are shown in Figure 3.16 and in the video below. In each example, matter may look different after the change occurs, but its still the same substance with the same chemical properties. For example, smaller pieces of wood have the ability to burn just as larger logs do. MEDIA Click image to the left or use the URL below. URL: Because the type of matter remains the same with physical changes, the changes are often easy to undo. For example, braided hair can be unbraided again. Melted chocolate can be put in a fridge to re-harden. Dissolving salt in water is also a physical change. How do you think you could undo it? | text | null |
L_0768 | changes in matter | T_3933 | Did you ever make a "volcano," like the one in Figure 3.17, using baking soda and vinegar? What happens when the two substances combine? They produce an eruption of foamy bubbles. This happens because of a chemical change. A chemical change occurs when matter changes chemically into an entirely different substance with different chemical properties. When vinegar and baking soda combine, they form carbon dioxide, a gas that causes the bubbles. Its the same gas that gives soft drinks their fizz. Not all chemical changes are as dramatic as this "volcano." Some are slower and less obvious. Figure 3.18 and the video below show other examples of chemical changes. MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0768 | changes in matter | T_3934 | How can you tell whether a chemical change has occurred? Often, there are clues. Several are demonstrated in Figures 3.17 and 3.18 and in the video below. MEDIA Click image to the left or use the URL below. URL: To decide whether a chemical change has occurred, look for these signs: Gas bubbles are released. (Example: Baking soda and vinegar mix and produce bubbles.) Something changes color. (Example: Leaves turn from green to other colors.) An odor is produced. (Example: Logs burn and smell smoky.) A solid comes out of a solution. (Example: Eggs cook and a white solid comes out of the clear liquid part of the egg.) | text | null |
L_0768 | changes in matter | T_3935 | Because chemical changes produce new substances, they often cannot be undone. For example, you cant change a fried egg back to a raw egg. Some chemical changes can be reversed, but only by other chemical changes. For example, to undo the tarnish on copper pennies, you can place them in vinegar. The acid in the vinegar reacts with the tarnish. This is a chemical change that makes the pennies bright and shiny again. You can try this yourself at home to see how well it works. | text | null |
L_0768 | changes in matter | T_3936 | If you build a campfire, like the one in Figure 3.19, you start with a large stack of sticks and logs. As the fire burns, the stack slowly shrinks. By the end of the evening, all thats left is a small pile of ashes. What happened to the matter that you started with? Was it destroyed by the flames? It may seem that way, but in fact, the same amount of matter still exists. The wood changed not only to ashes but also to carbon dioxide, water vapor, and other gases. The gases floated off into the air, leaving behind just the ashes. Assume you had measured the mass of the wood before you burned it. Assume you had also trapped the gases released by the burning wood and measured their mass and the mass of the ashes. What would you find? The ashes and gases combined have the same mass as the wood you started with. This example illustrates the law of conservation of mass. The law states that matter cannot be created or destroyed. Even when matter goes through physical or chemical changes, the total mass of matter always remains the same. (In the chapter Nuclear Chemistry, you will learn about nuclear reactions, in which mass is converted into energy. But other than that, the law of conservation of mass holds.) For a fun challenge, try to apply the law of conservation of mass to a scene from a Harry Potter film at this link: . | text | null |
L_0769 | solids liquids gases and plasmas | T_3937 | Ice is an example of solid matter. A solid is matter that has a fixed volume and a fixed shape. Figure 4.3 shows examples of matter that are usually solids under Earth conditions. In the figure, salt and cellulose are examples of crystalline solids. The particles of crystalline solids are arranged in a regular repeating pattern. The steaks and candle wax are examples of amorphous ("shapeless") solids. Their particles have no definite pattern. | text | null |
L_0769 | solids liquids gases and plasmas | T_3938 | Ocean water is an example of a liquid. A liquid is matter that has a fixed volume but not a fixed shape. Instead, a liquid takes the shape of its container. If the volume of a liquid is less than the volume of its container, the top surface will be exposed to the air, like the oil in the bottles in Figure 4.4. Two interesting properties of liquids are surface tension and viscosity. Surface tension is a force that pulls particles at the exposed surface of a liquid toward other liquid particles. Surface tension explains why water forms droplets, like those in Figure 4.5. Viscosity is a liquids resistance to flowing. Thicker liquids are more viscous than thinner liquids. For example, the honey in Figure 4.5 is more viscous than the vinegar. You can learn more about surface tension and viscosity at these URLs: http://io9.com/5668221/an-experiment-with-soap-water-pepper-and-surface-tension http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Viscosity-840.html (1:40) MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0769 | solids liquids gases and plasmas | T_3938 | Ocean water is an example of a liquid. A liquid is matter that has a fixed volume but not a fixed shape. Instead, a liquid takes the shape of its container. If the volume of a liquid is less than the volume of its container, the top surface will be exposed to the air, like the oil in the bottles in Figure 4.4. Two interesting properties of liquids are surface tension and viscosity. Surface tension is a force that pulls particles at the exposed surface of a liquid toward other liquid particles. Surface tension explains why water forms droplets, like those in Figure 4.5. Viscosity is a liquids resistance to flowing. Thicker liquids are more viscous than thinner liquids. For example, the honey in Figure 4.5 is more viscous than the vinegar. You can learn more about surface tension and viscosity at these URLs: http://io9.com/5668221/an-experiment-with-soap-water-pepper-and-surface-tension http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Viscosity-840.html (1:40) MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0769 | solids liquids gases and plasmas | T_3939 | Water vapor is an example of a gas. A gas is matter that has neither a fixed volume nor a fixed shape. Instead, a gas takes both the volume and the shape of its container. It spreads out to take up all available space. You can see an example in Figure 4.6. | text | null |
L_0769 | solids liquids gases and plasmas | T_3940 | Youre probably less familiar with plasmas than with solids, liquids, and gases. Yet, most of the universe consists of plasma. Plasma is a state of matter that resembles a gas but has certain properties that a gas does not have. Like a gas, plasma lacks a fixed volume and shape. Unlike a gas, plasma can conduct electricity and respond to magnetism. Thats because plasma contains charged particles called ions. This gives plasma other interesting properties. For example, it glows with light. Where can you find plasmas? Two examples are shown in Figure 4.7. The sun and other stars consist of plasma. Plasmas are also found naturally in lightning and the polar auroras (northern and southern lights). Artificial plasmas are found in fluorescent lights, plasma TV screens, and plasma balls like the one that opened this chapter. You can learn more about plasmas at this URL: (2:58). MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0769 | solids liquids gases and plasmas | T_3941 | Why do different states of matter have different properties? Its because of differences in energy at the level of atoms and molecules, the tiny particles that make up matter. | text | null |
L_0769 | solids liquids gases and plasmas | T_3942 | Energy is defined as the ability to cause changes in matter. You can change energy from one form to another when you lift your arm or take a step. In each case, energy is used to move matter you. The energy of moving matter is called kinetic energy. | text | null |
L_0769 | solids liquids gases and plasmas | T_3943 | The particles that make up matter are also constantly moving. They have kinetic energy. The theory that all matter consists of constantly moving particles is called the kinetic theory of matter. You can learn more about it at the URL below. | text | null |
L_0769 | solids liquids gases and plasmas | T_3944 | Particles of matter of the same substance, such as the same element, are attracted to one another. The force of attraction tends to pull the particles closer together. The particles need a lot of kinetic energy to overcome the force of attraction and move apart. Its like a tug of war between opposing forces. The kinetic energy of individual particles is on one side, and the force of attraction between different particles is on the other side. The outcome of the "war" depends on the state of matter. This is illustrated in Figure 4.8 and in the animation at this URL: http://w In solids, particles dont have enough kinetic energy to overcome the force of attraction between them. The particles are packed closely together and cannot move around. All they can do is vibrate. This explains why solids have a fixed volume and shape. In liquids, particles have enough kinetic energy to partly overcome the force of attraction between them. They can slide past one another but not pull completely apart. This explains why liquids can change shape but have a fixed volume. In gases, particles have a lot of kinetic energy. They can completely overcome the force of attraction between them and move apart. This explains why gases have neither a fixed volume nor a fixed shape. | text | null |
L_0771 | changes of state | T_3950 | What causes clouds to form? And in general, how does matter change from one state to another? As you may have guessed, changes in energy are involved. | text | null |
L_0771 | changes of state | T_3951 | Changes of state are physical changes in matter. They are reversible changes that do not involve changes in matters chemical makeup or chemical properties. Common changes of state include melting, freezing, sublimation, deposition, condensation, and vaporization. These changes are shown in Figure 4.18. Each is described in detail below. | text | null |
L_0771 | changes of state | T_3952 | Energy is always involved in changes of state. Matter either loses or absorbs energy when it changes from one state to another. For example, when matter changes from a liquid to a solid, it loses energy. The opposite happens when matter changes from a solid to a liquid. For a solid to change to a liquid, matter must absorb energy from its surroundings. The amount of energy in matter can be measured with a thermometer. Thats because a thermometer measures temperature, and temperature is the average kinetic energy of the particles of matter. You can learn more about energy, temperature, and changes of state at this URL: http://hogan.chem.lsu.edu/matter/chap26/animate3/an2 | text | null |
L_0771 | changes of state | T_3953 | Think about how you would make ice cubes in a tray. First you would fill the tray with water from a tap. Then you would place the tray in the freezer compartment of a refrigerator. The freezer is very cold. What happens next? | text | null |
L_0771 | changes of state | T_3954 | The warmer water in the tray loses heat to the colder air in the freezer. The water cools until its particles no longer have enough energy to slide past each other. Instead, they remain in fixed positions, locked in place by the forces of attraction between them. The liquid water has changed to solid ice. Another example of liquid water changing to solid ice is pictured in Figure 4.19. The process in which a liquid changes to a solid is called freezing. The temperature at which a liquid changes to a solid is its freezing point. The freezing point of water is 0C (32F). Other types of matter may have higher or lower freezing points. For example, the freezing point of iron is 1535C. The freezing point of oxygen is -219C. | text | null |
L_0771 | changes of state | T_3955 | If you took ice cubes out of a freezer and left them in a warm room, the ice would absorb energy from the warmer air around it. The energy would allow the particles of frozen water to overcome some of the forces of attraction holding them together. They would be able to slip out of the fixed positions they held as ice. In this way, the solid ice would turn to liquid water. The process in which a solid changes to a liquid is called melting. The melting point is the temperature at which a solid changes to a liquid. For a given type of matter, the melting point is the same as the freezing point. What is the melting point of ice? What is the melting point of iron, pictured in Figure 4.20? | text | null |
L_0771 | changes of state | T_3956 | If you fill a pot with cool tap water and place the pot on a hot stovetop, the water heats up. Heat energy travels from the stovetop to the pot, and the water absorbs the energy from the pot. What happens to the water next? | text | null |
L_0771 | changes of state | T_3957 | If water gets hot enough, it starts to boil. Bubbles of water vapor form in boiling water. This happens as particles of liquid water gain enough energy to completely overcome the force of attraction between them and change to the gaseous state. The bubbles rise through the water and escape from the pot as steam. The process in which a liquid boils and changes to a gas is called vaporization. The temperature at which a liquid boils is its boiling point. The boiling point of water is 100C (212F). Other types of matter may have higher or lower boiling points. For example, the boiling point of table salt is 1413C. The boiling point of nitrogen is -196C. | text | null |
L_0771 | changes of state | T_3958 | A liquid can also change to a gas without boiling. This process is called evaporation. It occurs when particles at the exposed surface of a liquid absorb just enough energy to pull away from the liquid and escape into the air. This happens faster at warmer temperatures. Look at the puddle in Figure 4.21. It formed in a pothole during a rain shower. The puddle will eventually evaporate. It will evaporate faster if the sun comes out and heats the water than if the sky remains cloudy. | text | null |
L_0771 | changes of state | T_3959 | If you take a hot shower in a closed bathroom, the mirror is likely to "fog" up. The "fog" consists of tiny droplets of water that form on the cool surface of the mirror. Why does this happen? Some of the hot water from the shower evaporates, so the air in the bathroom contains a lot of water vapor. When the water vapor contacts cooler surfaces, such as the mirror, it cools and loses energy. The cooler water particles no longer have enough energy to overcome the forces of attraction between them. They come together and form droplets of liquid water. The process in which a gas changes to a liquid is called condensation. Other examples of condensation are shown in Figure 4.22. A gas condenses when it is cooled below its boiling point. At what temperature does water vapor condense? | text | null |
L_0771 | changes of state | T_3959 | If you take a hot shower in a closed bathroom, the mirror is likely to "fog" up. The "fog" consists of tiny droplets of water that form on the cool surface of the mirror. Why does this happen? Some of the hot water from the shower evaporates, so the air in the bathroom contains a lot of water vapor. When the water vapor contacts cooler surfaces, such as the mirror, it cools and loses energy. The cooler water particles no longer have enough energy to overcome the forces of attraction between them. They come together and form droplets of liquid water. The process in which a gas changes to a liquid is called condensation. Other examples of condensation are shown in Figure 4.22. A gas condenses when it is cooled below its boiling point. At what temperature does water vapor condense? | text | null |
L_0771 | changes of state | T_3960 | Solids that change to gases generally first pass through the liquid state. However, sometimes solids change directly to gases and skip the liquid state. The reverse can also occur. Sometimes gases change directly to solids. | text | null |
L_0771 | changes of state | T_3961 | The process in which a solid changes directly to a gas is called sublimation. It occurs when the particles of a solid absorb enough energy to completely overcome the force of attraction between them. Dry ice (solid carbon dioxide, CO2 ) is an example of a solid that undergoes sublimation. Figure 4.23 shows a chunk of dry ice changing directly to carbon dioxide gas. Sometimes snow undergoes sublimation as well. This is most likely to occur on sunny winter days when the air is very dry. What gas does snow become? | text | null |
L_0771 | changes of state | T_3962 | The opposite of sublimation is deposition. This is the process in which a gas changes directly to a solid without going through the liquid state. It occurs when gas particles become very cold. For example, when water vapor in the air contacts a very cold windowpane, the water vapor may change to tiny ice crystals on the glass. The ice crystals are called frost. You can see an example in Figure 4.24. | text | null |
L_0805 | atoms | T_4146 | Identify the conditions that will speed up or slow down the dissolving process. | text | null |
L_0805 | atoms | T_4147 | Did you ever drink the tea before all the sugar has dissolved? Did you ever notice that some of the sugar is sitting at the bottom of the glass? Q: What could you do to dissolve the sugar faster? A: The rate of dissolving is caused by several factors. These factors include stirring, temperature, and the size of the particles. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0805 | atoms | T_4148 | What would happen if you added sugar to iced tea and did not stir the liquid? Thats right, most of the sugar you added would fall to the bottom of the glass. Like most people, when you add sugar to a liquid, you stir it, but why? For most of us, it is automatic. How many times have you added something to a liquid and immediately grabbed our spoon and started to stir. Have you ever thought about why we stir? So, why do we stir liquids when we add other ingredients? Stirring a liquid while you are mixing in another ingredient speeds up the rate of dissolving. This is because it helps distribute the particles that are being dissolved. What happens when you add sugar (the solute) to iced tea (the solvent) and then stir the tea? The obvious answer is that the sugar will dissolve. The more quickly you stir, the faster the sugar will dissolve. What if you dont stir the tea? Will the sugar still dissolve? It may eventually dissolve, but it will take much longer. You can think of stirring like adding energy to the process. What are other ways to add energy? | text | null |
L_0805 | atoms | T_4149 | What do you think will happen when you add the same amount of sugar to cups of hot and cold tea? Will the sugar dissolve at the same rate? Is that why people start with warm water when they make iced tea? The temperature of the solvent is an important factor in how fast something dissolves. Temperature affects how fast a solute dissolves. Generally, a solute dissolves faster in a warmer solvent. It dissolves more slowly in a cooler solvent. Think about that next time you make iced tea. | text | null |
L_0805 | atoms | T_4150 | There is another factor that affects the rate of dissolving. The particle size of solute particles affects the rate. Smaller particles have greater surface area. Think of a large block of Legos. When all the blocks are stuck together you can measure their surface area. Now take all the blocks apart and measure their individual surface areas. Which has more? Greater surface area provides more contact between the particles and the solvent. For example, if you put granulated sugar in a glass of iced tea, it will dissolve more quickly. If you put a sugar cube in a glass of iced tea, it will dissolve more slowly. Thats because all those tiny particles of granulated sugar have greater surface area than a single sugar cube. | text | null |
L_0805 | atoms | T_4151 | 1. List three factors that affect the rate at which a solute dissolves in a solvent. 2. Gina is trying to dissolve bath salts in her bathwater. How could she speed up the rate of dissolving? | text | null |
L_0805 | atoms | T_4152 | By clicking a link below, you will leave the CK-12 site and open an external site in a new tab. This page will remain open in the original tab. | text | null |
L_0812 | boiling | T_4173 | Steam actually consists of tiny droplets of liquid water. What you cant see in the picture is the water vapor that is also present in the air above the spring. Water vapor is water in the gaseous state. It constantly rises up from the surface of boiling hot water. Why? At high temperatures, particles of a liquid gain enough energy to completely overcome the force of attraction between them, so they change to a gas. The gas forms bubbles that rise to the surface of the liquid because gas is less dense than liquid. The bubbling up of the liquid is called boiling. When the bubbles reach the surface, the gas escapes into the air. The entire process in which a liquid boils and changes to a gas that escapes into the air is called vaporization. Q: Why does steam form over the hot spring pictured above? A: Steam forms when some of the water vapor from the boiling water cools in the air and condenses to form droplets of liquid water. | text | null |
L_0812 | boiling | T_4174 | Vaporization is easily confused with evaporation, but the two processes are not the same. Evaporation also changes a liquid to a gas, but it doesnt involve boiling. Instead, evaporation occurs when particles at the surface of a liquid gain enough energy to escape into the air. This happens without the liquid becoming hot enough to boil. | text | null |
L_0812 | boiling | T_4175 | The temperature at which a substance boils and changes to a gas is called its boiling point. Boiling point is a physical property of matter. The boiling point of pure water is 100 C. Other substances may have higher or lower boiling points. Several examples are listed in the Table 1.1. Pure water is included in the table for comparison. Substance Hydrogen Nitrogen Carbon dioxide Ammonia Pure water Salty ocean water Petroleum Olive oil Sodium chloride Boiling Point ( C) -253 -196 -79 -36 100 101 210 300 1413 Q: Assume you want to get the salt (sodium chloride) out of salt water. Based on information in the table, how could you do it? A: You could heat the salt water to 101 C. The water would boil and vaporize but the salt would not. Instead, the salt would be left behind as solid particles. Q: Oxygen is a gas at room temperature (20 C). What does this tell you about its boiling point? A: The boiling point of oxygen must be lower than 20 C. Otherwise, it would be a liquid at room temperature. | text | null |
L_0818 | calculating derived quantities | T_4190 | Derived quantities are quantities that are calculated from two or more measurements. Derived quantities cannot be measured directly. They can only be computed. Many derived quantities are calculated in physical science. Three examples are area, volume, and density. | text | null |
L_0818 | calculating derived quantities | T_4191 | The area of a surface is how much space it covers. Its easy to calculate the area of a surface if it has a regular shape, such as the blue rectangle in the sketch below. You simply substitute measurements of the surface into the correct formula. To find the area of a rectangular surface, use this formula: Area (rectangular surface) = length width (l w) Q: What is the area of the blue rectangle? A: Substitute the values for the rectangles length and width into the formula for area: Area = 9 cm 5 cm = 45 cm2 Q: Can you use this formula to find the area of a square surface? A: Yes, you can. A square has four sides that are all the same length, so you would substitute the same value for both length and width in the formula for the area of a rectangle. | text | null |
L_0818 | calculating derived quantities | T_4192 | The volume of a solid object is how much space it takes up. Its easy to calculate the volume of a solid if it has a simple, regular shape, such as the rectangular solid pictured in the sketch below. To find the volume of a rectangular solid, use this formula: Volume (rectangular solid) = length width height (l w h) Q: What is the volume of the blue rectangular solid? A: Substitute the values for the rectangular solids length, width, and height into the formula for volume: Volume = 10 cm 3 cm 5 cm = 150 cm3 | text | null |
L_0818 | calculating derived quantities | T_4193 | Density is a quantity that expresses how much matter is packed into a given space. The amount of matter is its mass, and the space it takes up is its volume. To calculate the density of an object, then, you would use this formula: Density = mass volume Q: The volume of the blue rectangular solid above is 150 cm3 . If it has a mass of 300 g, what is its density? A: The density of the rectangular solid is: Density = 300 g = 2 g/cm3 150 cm3 Q: Suppose you have two boxes that are the same size but one box is full of feathers and the other box is full of books. Which box has greater density? A: Both boxes have the same volume because they are the same size. However, the books have greater mass than the feathers. Therefore, the box of books has greater density. | text | null |
L_0818 | calculating derived quantities | T_4194 | A given derived quantity, such as area, is always expressed in the same type of units. For example, area is always expressed in squared units, such as cm2 or m2 . If you calculate area and your answer isnt in squared units, then you have made an error. Q: What units are used to express volume? A: Volume is expressed in cubed units, such as cm3 or m3 . Q: A certain derived quantity is expressed in the units kg/m3 . Which derived quantity is it? A: The derived quantity is density, which is mass (kg) divided by volume (m3 ). | text | null |
L_0825 | changes of state | T_4214 | The water droplets of fog form from water vapor in the air. Fog disappears when the water droplets change back to water vapor. These changes are examples of changes of state. A change of state occurs whenever matter changes from one state to another. Common states of matter on Earth are solid, liquid, and gas. Matter may change back and forth between any two of these states. Changes of state are physical changes in matter. They are reversible changes that do not change matters chemical makeup or chemical properties. For example, when fog changes to water vapor, it is still water and can change back to liquid water again. | text | null |
L_0825 | changes of state | T_4215 | Several processes are involved in common changes of state. They include melting, freezing, sublimation, deposition, condensation, and evaporation. The Figure 1.1 shows how matter changes in each of these processes. Q: Which two processes result in matter changing to the solid state? A: The processes are deposition, in which matter changes from a gas to a solid, and freezing, in which matter changes from a liquid to a solid. | text | null |
L_0825 | changes of state | T_4216 | Suppose that you leave some squares of chocolate candy in the hot sun. A couple of hours later, you notice that the chocolate has turned into a puddle like the one pictured in the Figure 1.2. Q: What happened to the chocolate? A: The chocolate melted. It changed from a solid to a liquid. In order for solid chocolate to melt and change to a liquid, the particles of chocolate must gain energy. The chocolate pictured in the Figure 1.2 gained energy from sunlight. Energy is the ability to cause changes in matter, and it is always involved in changes of state. When matter changes from one state to another, it either absorbs energyas when chocolate meltsor loses energy. For example, if you were to place the melted chocolate in a refrigerator, it would lose energy to the cold air inside the refrigerator. As a result, the liquid chocolate would change to a solid Q: Why is energy always involved in changes of state? A: The energy of particles of matter determines the matters state. Particles of a gas have more energy than particles of a liquid, and particles of a liquid have more energy than particles of a solid. Therefore, in order for matter to change from a solid to a liquid or from a liquid to a gas, particles of matter must absorb energy. In order for matter to change from a gas to a liquid or from a liquid to a solid, particles of matter must lose energy. | text | null |
L_0825 | changes of state | T_4216 | Suppose that you leave some squares of chocolate candy in the hot sun. A couple of hours later, you notice that the chocolate has turned into a puddle like the one pictured in the Figure 1.2. Q: What happened to the chocolate? A: The chocolate melted. It changed from a solid to a liquid. In order for solid chocolate to melt and change to a liquid, the particles of chocolate must gain energy. The chocolate pictured in the Figure 1.2 gained energy from sunlight. Energy is the ability to cause changes in matter, and it is always involved in changes of state. When matter changes from one state to another, it either absorbs energyas when chocolate meltsor loses energy. For example, if you were to place the melted chocolate in a refrigerator, it would lose energy to the cold air inside the refrigerator. As a result, the liquid chocolate would change to a solid Q: Why is energy always involved in changes of state? A: The energy of particles of matter determines the matters state. Particles of a gas have more energy than particles of a liquid, and particles of a liquid have more energy than particles of a solid. Therefore, in order for matter to change from a solid to a liquid or from a liquid to a gas, particles of matter must absorb energy. In order for matter to change from a gas to a liquid or from a liquid to a solid, particles of matter must lose energy. | text | null |
L_0827 | chemical and solar cells | T_4218 | Chemical cells are found in batteries. They produce voltage by means of chemical reactions. Chemical cells have two electrodes, which are strips of different materials, such as zinc and carbon. The electrodes are suspended in an electrolyte. This is a substance that contains free ions, which can carry electric current. The electrolyte may be either a paste, in which case the cell is called a dry cell, or a liquid, in which case the cell is called a wet cell. Flashlight batteries contain dry cells. Car batteries contain wet cells. The Figure 1.1 shows how a battery works. The diagram represents the simplest type of battery, one that contains a single chemical cell. Both dry and wet cells work the same basic way. The electrodes react chemically with the electrolyte, causing one electrode to give up electrons and the other electrode to accept electrons. Electrons flow through the electrolyte from the negative to positive electrode. The electrodes extend out of the battery for the attachment of wires that carry the current. The current can be used to power a light bulb or other electric device. | text | null |
L_0827 | chemical and solar cells | T_4219 | Solar cells convert the energy in sunlight to electrical energy. Solar cells are also called photovoltaic (PV) cells because they use light (photo-) to produce voltage (-voltaic). Solar cells contain a material such as silicon that absorbs light energy. The energy knocks electrons loose so they can flow freely and produce a difference in electric potential energy, or voltage. The flow of electrons creates electric current. Solar cells have positive and negative contacts, like the terminals in chemical cells. If the contacts are connected with wire, current flows from the negative to positive contact. The Figure 1.2 shows how a solar cell works. | text | null |
L_0827 | chemical and solar cells | T_4219 | Solar cells convert the energy in sunlight to electrical energy. Solar cells are also called photovoltaic (PV) cells because they use light (photo-) to produce voltage (-voltaic). Solar cells contain a material such as silicon that absorbs light energy. The energy knocks electrons loose so they can flow freely and produce a difference in electric potential energy, or voltage. The flow of electrons creates electric current. Solar cells have positive and negative contacts, like the terminals in chemical cells. If the contacts are connected with wire, current flows from the negative to positive contact. The Figure 1.2 shows how a solar cell works. | text | null |
L_0829 | chemical change | T_4223 | A chemical change occurs whenever matter changes into an entirely different substance with different chemical properties. A chemical change is also called a chemical reaction. Many complex chemical changes occur to produce the explosions of fireworks. An example of a simpler chemical change is the burning of methane. Methane is the main component of natural gas, which is burned in many home furnaces. During burning, methane combines with oxygen in the air to produce entirely different chemical substances, including the gases carbon dioxide and water vapor. Click image to the left or use the URL below. URL: | text | null |
L_0829 | chemical change | T_4224 | Most chemical changes are not as dramatic as exploding fireworks, so how can you tell whether a chemical change has occurred? There are usually clues. You just need to know what to look for. A chemical change has probably occurred if bubbles are released, there is a change of color, or an odor is produced. Other clues include the release of heat, light, or loud sounds. Examples of chemical changes that produce these clues are shown in the Figure 1.1. Q: In addition to iron rusting, what is another example of matter changing color? Do you think this color change is a sign that a new chemical substance has been produced? A: Another example of matter changing color is a penny changing from reddish brown to greenish brown as it becomes tarnished. The color change indicates that a new chemical substance has been produced. Copper on the surface of the penny has combined with oxygen in the air to produce a different substance called copper oxide. Q: Besides food spoiling, what is another change that produces an odor? Is this a chemical change? A: When wood burns, it produces a smoky odor. Burning is a chemical change. Q: Which signs of chemical change do fireworks produce? A: Fireworks produce heat, light, and loud sounds. These are all signs of chemical change. | text | null |
L_0829 | chemical change | T_4225 | Because chemical changes produce new substances, they often cannot be undone. For example, you cant change ashes from burning logs back into wood. Some chemical changes can be reversed, but only by other chemical changes. For example, to undo tarnish on copper pennies, you can place them in vinegar. The acid in the vinegar combines with the copper oxide of the tarnish. This changes the copper oxide back to copper and oxygen, making the pennies reddish brown again. You can try this at home to see how well it works. | text | null |
L_0832 | chemical properties of matter | T_4232 | Chemical properties are properties that can be measured or observed only when matter undergoes a change to become an entirely different kind of matter. For example, the ability of iron to rust can only be observed when iron actually rusts. When it does, it combines with oxygen to become a different substance called iron oxide. Iron is very hard and silver in color, whereas iron oxide is flakey and reddish brown. Besides the ability to rust, other chemical properties include reactivity and flammability. | text | null |
L_0832 | chemical properties of matter | T_4233 | Reactivity is the ability of matter to combine chemically with other substances. Some kinds of matter are extremely reactive; others are extremely unreactive. For example, potassium is very reactive, even with water. When a pea- sized piece of potassium is added to a small amount of water, it reacts explosively. You can observe this reaction in the video below. (Caution: Dont try this at home!) In contrast, noble gases such as helium almost never react with any other substances. Click image to the left or use the URL below. URL: | text | null |
L_0832 | chemical properties of matter | T_4234 | Flammability is the ability of matter to burn. When matter burns, it combines with oxygen and changes to different substances. Wood is an example of flammable matter, as seen in Figure 1.1. Q: How can you tell that wood ashes are a different substance than wood? A: Ashes have different properties than wood. For example, ashes are gray and powdery, whereas wood is brown and hard. Q: What are some other substances that have the property of flammability? A: Substances called fuels have the property of flammability. They include fossil fuels such as coal, natural gas, and petroleum, as well as fuels made from petroleum, such as gasoline and kerosene. Substances made of wood, such as paper and cardboard, are also flammable. | text | null |
L_0842 | condensation | T_4266 | The drops of water on the spider web are dewdrops. They formed overnight when warm moist air came into contact with the cooler spider web. Contact with the cooler web cooled the air. When air cools, it can hold less water vapor, so some of the water vapor in the air changed to liquid water. The process in which water vaporor another gaschanges to a liquid is called condensation. Another common example of condensation is pictured in the Figure 1.1. | text | null |
L_0842 | condensation | T_4267 | When air is very humid, it doesnt have to cool very much for water vapor in the air to start condensing. The temperature at which condensation occurs is called the dew point. The dew point varies depending on air temperature and moisture content. It is always less than or equal to the actual air temperature, but warmer air and moister air have dew points closer to the actual air temperature. Thats why glasses of cold drinks sweat more on a hot, humid day than they do on a cool, dry day. Q: What happens when air temperature reaches the dew point? A: When air temperature reaches the dew point, water vapor starts condensing. It may form dew (as on the spider web in the opening image), clouds, or fog. Dew forms on solid objects on the ground. Clouds form on tiny particles in the air high above the ground. Fog is a cloud that forms on tiny particles in the air close to the ground. | text | null |
L_0842 | condensation | T_4267 | When air is very humid, it doesnt have to cool very much for water vapor in the air to start condensing. The temperature at which condensation occurs is called the dew point. The dew point varies depending on air temperature and moisture content. It is always less than or equal to the actual air temperature, but warmer air and moister air have dew points closer to the actual air temperature. Thats why glasses of cold drinks sweat more on a hot, humid day than they do on a cool, dry day. Q: What happens when air temperature reaches the dew point? A: When air temperature reaches the dew point, water vapor starts condensing. It may form dew (as on the spider web in the opening image), clouds, or fog. Dew forms on solid objects on the ground. Clouds form on tiny particles in the air high above the ground. Fog is a cloud that forms on tiny particles in the air close to the ground. | text | null |
L_0842 | condensation | T_4268 | The water cycle continuously recycles Earths water. Condensation plays an important role in this cycle. Find condensation in the water cycle Figure 1.3. It changes water vapor in the atmosphere to liquid water that can fall to Earth again. Without condensation, the water cycle would be interrupted and Earths water could not recycle. Q: In the water cycle, what happens to water after it condenses? A: After water condenses, it may form clouds that produce precipitation such as rain. | text | null |
L_0844 | conservation of mass | T_4271 | It may seem as though burning destroys matter, but the same amount, or mass, of matter still exists after a campfire as before. Look at the sketch in Figure 1.1. It shows that when wood burns, it combines with oxygen and changes not only to ashes but also to carbon dioxide and water vapor. The gases float off into the air, leaving behind just the ashes. Suppose you had measured the mass of the wood before it burned and the mass of the ashes after it burned. Also suppose you had been able to measure the oxygen used by the fire and the gases produced by the fire. What would you find? The total mass of matter after the fire would be the same as the total mass of matter before the fire. Q: What can you infer from this example? A: You can infer that burning does not destroy matter. It just changes matter into different substances. | text | null |
L_0844 | conservation of mass | T_4272 | This burning campfire example illustrates a very important law in science: the law of conservation of mass. This law states that matter cannot be created or destroyed. Even when matter goes through a physical or chemical change, the total mass of matter always remains the same. Q: How could you show that the mass of matter remains the same when matter changes state? A: You could find the mass of a quantity of liquid water. Then you could freeze the water and find the mass of the ice. The mass before and after freezing would be the same, showing that mass is conserved when matter changes state. | text | null |
L_0855 | density | T_4306 | Density is an important physical property of matter. It reflects how closely packed the particles of matter are. When particles are packed together more tightly, matter has greater density. Differences in density of matter explain many phenomena, not just why helium balloons rise. For example, differences in density of cool and warm ocean water explain why currents such as the Gulf Stream flow through the oceans. Click image to the left or use the URL below. URL: To better understand density, think about a bowling ball and volleyball, pictured in the Figure 1.1. Imagine lifting each ball. The two balls are about the same size, but the bowling ball feels much heavier than the volleyball. Thats because the bowling ball is made of solid plastic, which contains a lot of tightly packed particles of matter. The volleyball, in contrast, is full of air, which contains fewer, more widely spaced particles of matter. In other words, the matter inside the bowling ball is denser than the matter inside the volleyball. Q: If you ever went bowling, you may have noticed that some bowling balls feel heavier than others even though they are the same size. How can this be? A: Bowling balls that feel lighter are made of matter that is less dense. | text | null |
L_0855 | density | T_4307 | The density of matter is actually the amount of matter in a given space. The amount of matter is measured by its mass, and the space matter takes up is measured by its volume. Therefore, the density of matter can be calculated with this formula: Density = mass volume Assume, for example, that a book has a mass of 500 g and a volume of 1000 cm3 . Then the density of the book is: Density = 500 g = 0.5 g/cm3 1000 cm3 Q: What is the density of a liquid that has a volume of 30 mL and a mass of 300 g? A: The density of the liquid is: Density = 300 g = 10 g/mL 30 mL | text | null |
L_0856 | deposition | T_4308 | Deposition refers to the process in which a gas changes directly to a solid without going through the liquid state. For example, when warm moist air inside a house comes into contact with a freezing cold windowpane, water vapor in the air changes to tiny ice crystals. The ice crystals are deposited on the glass, often in beautiful patterns like the leaves on the window above. Be aware that deposition has a different meaning in Earth science than in chemistry. In Earth science, deposition refers to the dropping of sediments by wind or water, rather than to a change of state. | text | null |
L_0856 | deposition | T_4309 | Deposition as a change of state often occurs in nature. For example, when warm moist air comes into contact with very cold surfacessuch as the ground or objects on the groundice crystals are deposited on them. These ice crystals are commonly called frost. Look at the dead leaf and blades of grass in the Figure 1.1. They are covered with frost. If you look closely, you can see the individual crystals of ice. You can watch a demonstration of frost forming on the side of a very cold can at the URL below. (Click on the mulitmedia choice Ice on a Can.). The ice in the can has been cooled to a very low temperature by adding salt to it. Q: In places with very cold winters, why might frost be more likely to form on the ground in the fall than in the winter? A: Frost forms when the air is warmer than the ground. This is more likely to be the case in the fall. In the winter, the air is likely to be as cold as the ground. Deposition also occurs high above the ground when water vapor in the air changes to ice crystals. In the atmosphere, the ice crystals are deposited on tiny dust particles. These ice crystals form clouds, generally cirrus clouds, which are thin and wispy. You can see cirrus clouds in the Figure 1.2. Q: Cirrus clouds form only at altitudes of 6 kilometers or higher above sea level. Do you know why? A: At this altitude, the atmosphere is always very cold. Unless the air is cold, water vapor will condense to form water droplets instead of ice crystals. | text | null |
L_0856 | deposition | T_4309 | Deposition as a change of state often occurs in nature. For example, when warm moist air comes into contact with very cold surfacessuch as the ground or objects on the groundice crystals are deposited on them. These ice crystals are commonly called frost. Look at the dead leaf and blades of grass in the Figure 1.1. They are covered with frost. If you look closely, you can see the individual crystals of ice. You can watch a demonstration of frost forming on the side of a very cold can at the URL below. (Click on the mulitmedia choice Ice on a Can.). The ice in the can has been cooled to a very low temperature by adding salt to it. Q: In places with very cold winters, why might frost be more likely to form on the ground in the fall than in the winter? A: Frost forms when the air is warmer than the ground. This is more likely to be the case in the fall. In the winter, the air is likely to be as cold as the ground. Deposition also occurs high above the ground when water vapor in the air changes to ice crystals. In the atmosphere, the ice crystals are deposited on tiny dust particles. These ice crystals form clouds, generally cirrus clouds, which are thin and wispy. You can see cirrus clouds in the Figure 1.2. Q: Cirrus clouds form only at altitudes of 6 kilometers or higher above sea level. Do you know why? A: At this altitude, the atmosphere is always very cold. Unless the air is cold, water vapor will condense to form water droplets instead of ice crystals. | text | null |
L_0858 | direct and alternating current | T_4313 | When current flows in just one direction, it is called direct current (DC). The diagram below shows how direct current flows through a simple circuit. An example of direct current is the current that flows through a battery- powered flashlight. In addition to batteries, solar cells and fuel cells can also provide direct current. | text | null |
L_0858 | direct and alternating current | T_4314 | When current keeps reversing direction, it is called alternating current (AC). You can see how it works in the two diagrams below. The current that comes from a power plant and supplies electricity to homes and businesses is alternating current. The current changes direction 60 times per second. It happens so quickly that the light bulb doesnt have a chance to stop glowing when the reversals occur. Q: Which type of current flows through the wires in your home? A: Alternating current from a power plant flows through the wires in a home. | text | null |
L_0860 | discovery of electromagnetism | T_4318 | Magnetism produced by electricity is called electromagnetism. Today, electromagnetism is used in many electric devices. However, until electromagnetism was discovered, scientists thought that electricity and magnetism were unrelated. A Danish scientist named Hans Christian Oersted (pictured in the Figure 1.1) changed all that. He made the important discovery that electric current creates a magnetic field. But like many other important discoveries in science, Oersteds discovery was just a lucky accident. | text | null |
L_0860 | discovery of electromagnetism | T_4319 | In 1820, Oersted was presenting a demonstration to some science students. Ironically, he was trying to show them that electricity and magnetism are not related. He placed a wire with electric current flowing through it next to a compass, which has a magnetic needle. As he expected, the needle of the compass didnt move. It just kept pointing toward Earths north magnetic pole. After the demonstration, a curious student held the wire near the compass again, but in a different direction. To Oersteds surprise, the needle of the compass swung toward the wire so it was no longer pointing north. Oersted was intrigued. He turned off the current in the wire to see what would happen to the compass needle. The needle swung back to its original position, pointing north once again. Oersted had discovered that an electric current creates a magnetic field. The magnetic field created by the current was strong enough to attract the needle of the nearby compass. | text | null |
L_0860 | discovery of electromagnetism | T_4320 | Oersted wanted to learn more about the magnetic field created by a current. He placed a compass at different locations around a wire with current flowing through it. You can see what he found in the Figure 1.2. The lines of magnetic force circle around the wire in a counterclockwise direction. | text | null |
L_0860 | discovery of electromagnetism | T_4321 | Just about a decade after Oersted discovered that electric current can produce a magnetic field, an English scientist named Michael Faraday discovered that the opposite is also true. A magnetic field can produce an electric current. This is known as Faradays law. The process by which a magnetic field produces current is called electromagnetic induction. It occurs when a conductor, such as a wire, crosses lines of force in a magnetic field. This can happen when a wire is moving relative to a magnet or a magnet is moving relative to a wire. | text | null |
L_0867 | electric charge and electric force | T_4338 | Electric charge is a physical property of particles or objects that causes them to attract or repel each other without touching. All electric charge is based on the protons and electrons in atoms. A proton has a positive electric charge, and an electron has a negative electric charge. In the Figure 1.1, you can see that positively charged protons (+) are located in the nucleus of the atom, while negatively charged electrons (-) move around the nucleus. | text | null |
L_0867 | electric charge and electric force | T_4339 | When it comes to electric charges, opposites attract, so positive and negative particles attract each other. You can see this in the Figure 1.2. This attraction explains why negative electrons keep moving around the positive nucleus of the atom. Like charges, on the other hand, repel each other, so two positive or two negative charges push apart. This is also shown in the diagram. The attraction or repulsion between charged particles is called electric force. The strength of electric force depends on the amount of electric charge on the particles and the distance between them. Larger charges or shorter distances result in greater force. Q: How do positive protons stay close together inside the nucleus of the atom if like charges repel each other? A: Other, stronger forces in the nucleus hold the protons together. | text | null |
L_0867 | electric charge and electric force | T_4339 | When it comes to electric charges, opposites attract, so positive and negative particles attract each other. You can see this in the Figure 1.2. This attraction explains why negative electrons keep moving around the positive nucleus of the atom. Like charges, on the other hand, repel each other, so two positive or two negative charges push apart. This is also shown in the diagram. The attraction or repulsion between charged particles is called electric force. The strength of electric force depends on the amount of electric charge on the particles and the distance between them. Larger charges or shorter distances result in greater force. Q: How do positive protons stay close together inside the nucleus of the atom if like charges repel each other? A: Other, stronger forces in the nucleus hold the protons together. | text | null |
L_0868 | electric circuits | T_4340 | A closed loop through which current can flow is called an electric circuit. In homes in the U.S., most electric circuits have a voltage of 120 volts. The amount of current (amps) a circuit carries depends on the number and power of electrical devices connected to the circuit. Home circuits generally have a safe upper limit of about 20 or 30 amps. | text | null |
L_0868 | electric circuits | T_4341 | All electric circuits have at least two parts: a voltage source and a conductor. They may have other parts as well, such as light bulbs and switches, as in the simple circuit seen in the Figure 1.1. The voltage source of this simple circuit is a battery. In a home circuit, the source of voltage is an electric power plant, which may supply electric current to many homes and businesses in a community or even to many communities. The conductor in most circuits consists of one or more wires. The conductor must form a closed loop from the source of voltage and back again. In the Figure 1.1, the wires are connected to both terminals of the battery, so they form a closed loop. Most circuits have devices such as light bulbs that convert electrical energy to other forms of energy. In the case of a light bulb, electrical energy is converted to light and thermal energy. Many circuits have switches to control the flow of current. When the switch is turned on, the circuit is closed and current can flow through it. When the switch is turned off, the circuit is open and current cannot flow through it. | text | null |
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