lessonID
stringlengths 6
6
| lessonName
stringlengths 3
52
| ID
stringlengths 6
21
| content
stringlengths 10
6.57k
| media_type
stringclasses 2
values | path
stringlengths 28
76
⌀ |
|---|---|---|---|---|---|
L_1004 | refraction | T_4792 | Physical properties include the state of matter. We know these states as solid, liquid, or gas. Properties can also include color and odor. For example, oxygen is a gas. It is a major part of the air we breathe. It is colorless and odorless. Chlorine is also a gas. In contrast to oxygen, chlorine is greenish in color. It has a strong, sharp odor. Have you ever smelled cleaning products used around your home? If so, you have probably smelled chlorine. Another place you might smell chlorine is at a public swimming pool. The chlorine is used to kill bacteria that may grow in the water. Other physical properties include hardness, freezing, and boiling points. Some substances have the ability to dissolve in other substances. Some substances cannot be dissolved. For example, salt easily dissolves in water. Oil does not dissolve in water. Some substances may have the ability to conduct heat or electricity. Some substances resist the flow of electricity and heat. These properties are demonstrated in Figure 1.1. Can you think of other physical properties? The video below compares physical properties. | text | null |
L_1004 | refraction | T_4793 | 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_1010 | saturation | T_4809 | The maximum amount of sugar that will dissolve in a liter of 20 C water is 2000 grams. A sugar-water solution that contains 1 liter of water and 2000 grams of sugar is said to be saturated. A saturated solution is a solution that contains as much solute as can dissolve in a given solvent at a given temperature. If you add more than 2000 grams of sugar to a liter of 20 C water, the extra sugar wont dissolve. On the other hand, a solution containing less than 2000 g of sugar in 1 liter of 20 C water can hold more sugar. A solution that contains less solute than can dissolve at a given temperature is called an unsaturated solution. You can learn more about saturated and unsaturated solutions by watching the video at this URL: . | text | null |
L_1010 | saturation | T_4810 | The Figure 1.1 shows the amounts of several different solutes that will dissolve in a liter of water at 20 C. As you can see from the graph, solutes vary greatly in how soluble they are in water. For example, you can dissolve almost 20 times as much sugar as baking soda in the same amount of water at this temperature. Q: Assume that a solution contains 150 grams of Epsom salt in 1 liter of water at 20 C. Is the solution saturated or unsaturated? A: A saturated solution of Epsom salt in 1 liter of 20 C water would contain 250 grams of Epsom salt. Therefore, this solution is unsaturated. It can hold another 100 grams of Epsom salt. Q: What do you think would happen if you added more than 250 grams of Epsom salt to a liter of 20 C water? A: Any Epsom salt over 250 grams would not dissolve in the solution. | text | null |
L_1015 | scientific measuring devices | T_4825 | Youve probably been using a ruler to measure length since you were in elementary school. But you may have made most of the measurements in English units of length, such as inches and feet. In science, length is most often measured in SI units, such as millimeters and centimeters. Many rulers have both types of units, one on each edge. The ruler pictured below has only SI units. It is shown here bigger than it really is so its easier to see the small lines, which measure millimeters. The large lines and numbers stand for centimeters. Count the number of small lines from the left end of the ruler (0.0). You should count 10 lines because there are 10 millimeters in a centimeter. Q: What is the length in millimeters of the red line above the metric ruler? A: The length of the red line is 32 mm. Q: What is the length of the red line in centimeters? A: The length of the red line is 3.2 cm. | text | null |
L_1015 | scientific measuring devices | T_4826 | Mass is the amount of matter in an object. Scientists often measure mass with a balance. A type of balance called a triple beam balance is pictured in Figure 1.1. To use this type of balance, follow these steps: 1. Place the object to be measured on the pan at the left side of the balance. 2. Slide the movable masses to the right until the right end of the arm is level with the balance mark. Start by moving the larger masses and then fine tune the measurement by moving the smaller masses as needed. 3. Read the three scales to determine the values of the masses that were moved to the right. Their combined mass is equal to the mass of the object. The Figure 1.2 is an enlarged version of the scales of the triple beam balance in Figure 1.1. It allows you to read the scales. The middle scale, which measures the largest movable mass, reads 300 grams. This is followed by the top scale, which reads 30 grams. The bottom scale reads 5.1 grams. Therefore, the mass of the object in the pan is 335.1 grams (300 grams + 30 grams + 5.1 grams). Q: What is the maximum mass this triple beam balance can measure? A: The maximum mass it can measure is 610 grams (500 grams + 100 grams + 10 grams). Q: What is the smallest mass this triple beam balance can measure? A: The smallest mass it can measure is one-tenth (0.1) of a gram. To measure very small masses, scientists use electronic balances, like the one in the Figure 1.3. This type of balance also makes it easier to make accurate measurements because mass is shown as a digital readout. In the picture, the balance is being used to measure the mass of a white powder on a plastic weighing tray. The mass of the tray alone would have to be measured first and then subtracted from the mass of the tray and powder together. The difference between the two masses is the mass of the powder alone. | text | null |
L_1015 | scientific measuring devices | T_4826 | Mass is the amount of matter in an object. Scientists often measure mass with a balance. A type of balance called a triple beam balance is pictured in Figure 1.1. To use this type of balance, follow these steps: 1. Place the object to be measured on the pan at the left side of the balance. 2. Slide the movable masses to the right until the right end of the arm is level with the balance mark. Start by moving the larger masses and then fine tune the measurement by moving the smaller masses as needed. 3. Read the three scales to determine the values of the masses that were moved to the right. Their combined mass is equal to the mass of the object. The Figure 1.2 is an enlarged version of the scales of the triple beam balance in Figure 1.1. It allows you to read the scales. The middle scale, which measures the largest movable mass, reads 300 grams. This is followed by the top scale, which reads 30 grams. The bottom scale reads 5.1 grams. Therefore, the mass of the object in the pan is 335.1 grams (300 grams + 30 grams + 5.1 grams). Q: What is the maximum mass this triple beam balance can measure? A: The maximum mass it can measure is 610 grams (500 grams + 100 grams + 10 grams). Q: What is the smallest mass this triple beam balance can measure? A: The smallest mass it can measure is one-tenth (0.1) of a gram. To measure very small masses, scientists use electronic balances, like the one in the Figure 1.3. This type of balance also makes it easier to make accurate measurements because mass is shown as a digital readout. In the picture, the balance is being used to measure the mass of a white powder on a plastic weighing tray. The mass of the tray alone would have to be measured first and then subtracted from the mass of the tray and powder together. The difference between the two masses is the mass of the powder alone. | text | null |
L_1015 | scientific measuring devices | T_4826 | Mass is the amount of matter in an object. Scientists often measure mass with a balance. A type of balance called a triple beam balance is pictured in Figure 1.1. To use this type of balance, follow these steps: 1. Place the object to be measured on the pan at the left side of the balance. 2. Slide the movable masses to the right until the right end of the arm is level with the balance mark. Start by moving the larger masses and then fine tune the measurement by moving the smaller masses as needed. 3. Read the three scales to determine the values of the masses that were moved to the right. Their combined mass is equal to the mass of the object. The Figure 1.2 is an enlarged version of the scales of the triple beam balance in Figure 1.1. It allows you to read the scales. The middle scale, which measures the largest movable mass, reads 300 grams. This is followed by the top scale, which reads 30 grams. The bottom scale reads 5.1 grams. Therefore, the mass of the object in the pan is 335.1 grams (300 grams + 30 grams + 5.1 grams). Q: What is the maximum mass this triple beam balance can measure? A: The maximum mass it can measure is 610 grams (500 grams + 100 grams + 10 grams). Q: What is the smallest mass this triple beam balance can measure? A: The smallest mass it can measure is one-tenth (0.1) of a gram. To measure very small masses, scientists use electronic balances, like the one in the Figure 1.3. This type of balance also makes it easier to make accurate measurements because mass is shown as a digital readout. In the picture, the balance is being used to measure the mass of a white powder on a plastic weighing tray. The mass of the tray alone would have to be measured first and then subtracted from the mass of the tray and powder together. The difference between the two masses is the mass of the powder alone. | text | null |
L_1015 | scientific measuring devices | T_4827 | At home, you might measure the volume of a liquid with a measuring cup. In science, the volume of a liquid might be measured with a graduated cylinder, like the one sketched below. The cylinder in the picture has a scale in milliliters (mL), with a maximum volume of 100 mL. Follow these steps when using a graduated cylinder to measure the volume of a liquid: 1. Place the cylinder on a level surface before adding the liquid. 2. After adding the liquid, move so your eyes are at the same level as the top of the liquid in the cylinder. 3. Read the mark on the glass that is at the lowest point of the curved surface of the liquid. This is called the meniscus. Q: What is the volume of the liquid in the graduated cylinder pictured above? A: The volume of the liquid is 67 mL. Q: What would the measurement be if you read the highest point of the curved surface of the liquid by mistake? A: The measurement would be 68 mL. | text | null |
L_1023 | series and parallel circuits | T_4844 | An electric circuit consists of at least one closed loop through which electric current can flow. Every circuit has a voltage source such as a battery and a conductor such as metal wire. A circuit may have other parts as well, such as lights and switches. In addition, a circuit may consist of one loop or two loops. | text | null |
L_1023 | series and parallel circuits | T_4845 | A circuit that consists of one loop is called a series circuit. You can see a simple series circuit below. If a series circuit is interrupted at any point in its single loop, no current can flow through the circuit and no devices in the circuit will work. In the series circuit below, if one light bulb burns out, the other light bulb wont work because it wont receive any current. Series circuits are commonly used in flashlights. Q: If one light bulb burns out in this series circuit, how can you tell which bulb it is? A: It may not be obvious, because neither bulb will light if one is burned out. You can tell which one it is only by replacing first one bulb and then the other to see which replacement results in both bulbs lighting up. | text | null |
L_1023 | series and parallel circuits | T_4846 | A circuit that has two loops is called a parallel circuit. A simple parallel circuit is sketched below. If one loop of a parallel circuit is interrupted, current can still flow through the other loop. In the parallel circuit below, if one light bulb burns out, the other light bulb will still work because current can bypass the burned-out bulb. The wiring in a house consists of parallel circuits. | text | null |
L_1026 | solenoid | T_4857 | A solenoid is a coil of wire with electric current flowing through it. You can see a solenoid in the Figure 1.1. Current flowing through the coil produces a magnetic field that has north and south poles. Click image to the left or use the URL below. URL: Q: How is a solenoid like a bar magnet? A: Like a bar magnet, a solenoid has north and south magnetic poles and is surrounded by a magnetic field. | text | null |
L_1026 | solenoid | T_4858 | Any wire with current flowing through it has a magnetic field. However, the magnetic field around a coiled wire is stronger than the magnetic field around a straight wire. Thats because each turn of the wire in the coil has its own magnetic field. Adding more turns to the coil of wire increases the strength of the field. Increasing the amount of current flowing through the coil also increases the strength of the magnetic field. | text | null |
L_1026 | solenoid | T_4859 | A solenoid is generally used to convert electromagnetic energy into motion. Solenoids are often used in devices that need a sudden burst of power to move a specific part. In addition to paintball markers, you can find solenoids in machines ranging from motor vehicles to electric dishwashers. Another device that uses solenoids is pictured in the Figure 1.2. | text | null |
L_1027 | solids | T_4860 | A snowflake is made of ice, or water in the solid state. A solid is one of four well-known states of matter. The other three states are liquid, gas, and plasma. Compared with these other states of matter, solids have particles that are much more tightly packed together. The particles are held rigidly in place by all the other particles around them so they cant slip past one another or move apart. This gives solids a fixed shape and a fixed volume. | text | null |
L_1027 | solids | T_4861 | Not all solids are alike. Some are crystalline solids; others are amorphous solids. Snowflakes are crystalline solids. Particles of crystalline solids are arranged in a regular repeating pattern, as you can see in the sketch in Figure chloride). Crystals of table salt are pictured in the Figure 1.1. Amorphous means shapeless. Particles of amorphous solids are arranged more-or-less at random and do not form crystals, as you can see in the Figure 1.2. An example of an amorphous solid is cotton candy, also shown in the Figure 1.2. Q: Look at the quartz rock and plastic bag pictured in the Figure 1.3. Which type of solid do you think each of them is? A: The quartz is a crystalline solid. Rocks are made of minerals and minerals form crystals. You can see their geometric shapes. The bag is an amorphous solid. It is made of the plastic and most plastics do not form crystals. | text | null |
L_1027 | solids | T_4861 | Not all solids are alike. Some are crystalline solids; others are amorphous solids. Snowflakes are crystalline solids. Particles of crystalline solids are arranged in a regular repeating pattern, as you can see in the sketch in Figure chloride). Crystals of table salt are pictured in the Figure 1.1. Amorphous means shapeless. Particles of amorphous solids are arranged more-or-less at random and do not form crystals, as you can see in the Figure 1.2. An example of an amorphous solid is cotton candy, also shown in the Figure 1.2. Q: Look at the quartz rock and plastic bag pictured in the Figure 1.3. Which type of solid do you think each of them is? A: The quartz is a crystalline solid. Rocks are made of minerals and minerals form crystals. You can see their geometric shapes. The bag is an amorphous solid. It is made of the plastic and most plastics do not form crystals. | text | null |
L_1027 | solids | T_4861 | Not all solids are alike. Some are crystalline solids; others are amorphous solids. Snowflakes are crystalline solids. Particles of crystalline solids are arranged in a regular repeating pattern, as you can see in the sketch in Figure chloride). Crystals of table salt are pictured in the Figure 1.1. Amorphous means shapeless. Particles of amorphous solids are arranged more-or-less at random and do not form crystals, as you can see in the Figure 1.2. An example of an amorphous solid is cotton candy, also shown in the Figure 1.2. Q: Look at the quartz rock and plastic bag pictured in the Figure 1.3. Which type of solid do you think each of them is? A: The quartz is a crystalline solid. Rocks are made of minerals and minerals form crystals. You can see their geometric shapes. The bag is an amorphous solid. It is made of the plastic and most plastics do not form crystals. | text | null |
L_1028 | solubility | T_4862 | Solubility is the amount of solute that can dissolve in a given amount of solvent at a given temperature. In a solution, the solute is the substance that dissolves, and the solvent is the substance that does the dissolving. For a given solvent, some solutes have greater solubility than others. For example, sugar is much more soluble in water than is salt. But even sugar has an upper limit on how much can dissolve. In a half liter of 20 C water, the maximum amount is 1000 grams. If you add more sugar than this, the extra sugar wont dissolve. You can compare the solubility of sugar, salt, and some other solutes in the Table 1.1. Solute Baking Soda Epsom salt Table salt Table sugar Grams of Solute that Will Dissolve in 0.5 L of Water (20 C) 48 125 180 1000 Q: How much salt do you think Rhonda added to the half-liter of water in her experiment? A: The solubility of salt is 180 grams per half liter of water at 20 C. If Rhonda had added less than 180 grams of salt to the half-liter of water, then all of it would have dissolved. Because some of the salt did not dissolve, she must have added more than 180 grams of salt to the water. | text | null |
L_1028 | solubility | T_4863 | Certain factors can change the solubility of a solute. Temperature is one such factor. How temperature affects solubility depends on the state of the solute, as you can see in the Figure 1.1. If a solute is a solid or liquid, increasing the temperature increases its solubility. For example, more sugar can dissolve in hot water than in cold water. If a solute is a gas, increasing the temperature decreases its solubility. For example, less carbon dioxide can dissolve in warm water than in cold water. The solubility of gases is also affected by pressure. Pressure is the force pushing against a given area. Increasing the pressure on a gas increases its solubility. Did you ever open a can of soda and notice how it fizzes out of the can? Soda contains dissolved carbon dioxide. Opening the can reduces the pressure on the gas in solution, so it is less soluble. As a result, some of the carbon dioxide comes out of solution and rushes into the air. Q: Which do you think will fizz more when you open it, a can of warm soda or a can of cold soda? A: A can of warm soda will fizz more because increasing the temperature decreases the solubility of a gas. Therefore, less carbon dioxide can remain dissolved in warm soda than in cold soda. | text | null |
L_1029 | solute and solvent | T_4864 | A solution forms when one substance is dissolved by another. The substance that dissolves is called the solute. The substance that dissolves it is called the solvent. The solute is present in a lesser amount that the solvent. When the solute dissolves, it separates into individual particles, which spread throughout the solvent. Q: In bronze, what are the solute and solvent? A: Because bronze consists mainly of copper, copper is the solvent and tin is the solute. The two metals are combined in a hot, molten state, but they form a solid solution at room temperature. | text | null |
L_1029 | solute and solvent | T_4865 | In the example of bronze, a solid (tin) is dissolved in another solid (copper). However, matter in any state can be the solute or solvent in a solution. For example, in a saltwater solution, a solid (salt) is dissolved in a liquid (water). The Table 1.1 describes examples of solutions consisting of solutes and solvents in various states of matter. Type of Solution: Example Gas dissolved in gas: dry air Gas dissolved in liquid: carbonated water Liquid dissolved in gas: moist air Liquid dissolved in liquid: vinegar Solid dissolved in liquid: sweet tea Solute oxygen carbon dioxide Solvent nitrogen water water acetic acid sugar air water tea | text | null |
L_1029 | solute and solvent | T_4866 | Salt isnt the only solute that dissolves in water. In fact, so many things dissolve in water that water is sometimes called the universal solvent. Water is such a good solvent because it is a very polar compound. A polar compound has positively and negatively charged ends. Solutes that are also charged are attracted to the oppositely charged ends of water molecules. This allows the water molecules to pull the solute particles apart. On the other hand, there are some substances that dont dissolve in water. Did you ever try to clean a paintbrush with water after painting with an oil-based paint? It doesnt work. Oil-based paint is nonpolar, so its particles arent charged. As a result, oil-based paint doesnt dissolve in water. (You can see how to dissolve oil-based paint in the Figure 1.1.) | text | null |
L_1029 | solute and solvent | T_4867 | These examples illustrate a general rule about solutes and solvents: like dissolves like. In other words, polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes. You can see below a students video demonstrating solutes that do and solutes that dont dissolve in water. Click image to the left or use the URL below. URL: | text | null |
L_1029 | solute and solvent | T_4868 | All solutes separate into individual particles when they dissolve, but the particles are different for ionic and covalent compounds. Ionic solutes separate into individual ions. Covalent solutes separate into individual molecules. Salt, or sodium chloride (NaCl), is an ionic compound. When it dissolves in water, it separates into positive sodium ions (Na+ ) and negative chloride ions (Cl ). You can see how this happens in the Figure 1.2. The negative oxygen ends of water molecules attract the positive sodium ions, and the positive hydrogen ends of water molecules attract the negative chloride ions. These forces of attraction pull the ions apart. The sugar glucose is a covalent compound. When sugar dissolves in water, it forms individual glucose molecules (C6 H12 O6 ). You can see how this happens in the Figure 1.3. Sugar is polar like water, so sugar molecules also have positive and negative ends. Forces of attraction between oppositely charged ends of water and sugar molecules pull individual sugar molecules away from the sugar crystal. Little by little, the sugar molecules are separated from the crystal and surrounded by water. Click image to the left or use the URL below. URL: | text | null |
L_1030 | solution concentration | T_4869 | A solution is a mixture of two or more substances in which dissolved particles are distributed evenly throughout the solution. The substance that dissolves in a solution is called the solute, and the substance that does the dissolving is called the solvent. The concentration of a solution is the amount of solute in a given amount of solution. A solution with a lot of dissolved solute has a high concentration and is called a concentrated solution. A solution with little dissolved solute has a low concentration and is called a dilute solution. | text | null |
L_1030 | solution concentration | T_4870 | The concentration of a solution represents the percentage of the solution that is the solute. You can calculate the concentration of a solution using this formula: Concentration = Mass (or volume) of Solute Mass (or volume) of Solution 100% For example, if a 100-gram solution of salt water contains 3 grams of salt, then its concentration is: Concentration = 3g 100g 100% = 3% Q: A 1000 mL container of brand A juice drink contains 250 mL of juice and 750 mL of water. A 600 mL container of brand B juice drink contains 200 mL of juice and 400 mL of water. Which brand of juice drink is more concentrated, brand A or brand B? 250 mL 1000 mL 100% = 25% 200 mL 600 mL 100% = 33% A: Concentration(A) = Concentration(B) = You can conclude that brand B is more concentrated. | text | null |
L_1031 | solutions | T_4871 | A solution is a mixture of two or more substances, but its not just any mixture. A solution is a homogeneous mixture. In a homogeneous mixture, the dissolved particles are spread evenly through the mixture. The particles of the solution are also too small to be seen or to settle out of the mixture. Click image to the left or use the URL below. URL: | text | null |
L_1031 | solutions | T_4872 | All solutions have two parts: the solute and the solvent. The solute is the substance that dissolves, and the solvent is the substance that dissolves the solute. Particles of solvent pull apart particles of solute, and the solute particles spread throughout the solvent. Salt water, such as the ocean water in the Figure 1.1, is an example of a solution. In a saltwater solution, salt is the solute and water is the solvent. Q: A scientist obtained a sample of water from the Atlantic Ocean and determined that the sample was about 3.5 percent dissolved salt. Predict the percent of dissolved salt in a sample of water from the Pacific Ocean. A: As a solution, ocean water is a homogeneous mixture. Therefore, no matter where the water sample is obtained, its composition will be about 3.5 percent dissolved salt. | text | null |
L_1031 | solutions | T_4873 | Not only salt, but many other solutes can dissolve in water. In fact, so many solutes can dissolve in water that water has been called the universal solvent. Even rocks can dissolve in water, which explains the cave that opened this article. A solute that can dissolve in a given solvent, such as water, is said to be soluble in that solvent. Conversely, a solute that cannot dissolve in a given solvent is said to be insoluble in that solvent. Although most solutes can dissolve in water, some solutes are insoluble in water. Oil is an example. Did you ever try to mix oil with water? No matter how well you mix the oil into the water, after the mixture stands for a while, the oil separates from the water and rises to the top. You can see how oil floats on ocean water in the Figure 1.2. | text | null |
L_1031 | solutions | T_4874 | Like salt water in the ocean, many solutions are normally in the liquid state. However, matter in any state can form a solution. An alloy, which is a mixture of a metal with one or more other substances, is a solid solution at room temperature. For example, the alloy bronze is a solution of copper and tin. Matter in the gaseous state can also form solutions. Q: What is an example of a gaseous solution? A: Air in the atmosphere is a gaseous solution. It is a mixture that contains mainly nitrogen and oxygen gases, with very small amounts of several other gases. The circle graph in the Figure 1.3 shows the composition of air. Oil from an oil spill floats on ocean water. Because air is a solution, it is homogeneous. In other words, no matter where you go, the air always contains the same proportion of gases that are shown in the graph. | text | null |
L_1031 | solutions | T_4874 | Like salt water in the ocean, many solutions are normally in the liquid state. However, matter in any state can form a solution. An alloy, which is a mixture of a metal with one or more other substances, is a solid solution at room temperature. For example, the alloy bronze is a solution of copper and tin. Matter in the gaseous state can also form solutions. Q: What is an example of a gaseous solution? A: Air in the atmosphere is a gaseous solution. It is a mixture that contains mainly nitrogen and oxygen gases, with very small amounts of several other gases. The circle graph in the Figure 1.3 shows the composition of air. Oil from an oil spill floats on ocean water. Because air is a solution, it is homogeneous. In other words, no matter where you go, the air always contains the same proportion of gases that are shown in the graph. | text | null |
L_1034 | specific heat | T_4883 | Specific heat is a measure of how much energy it takes to raise the temperature of a substance. It is the amount of energy (in joules) needed to raise the temperature of 1 gram of the substance by 1 C. Specific heat is a property that is specific to a given type of matter. Thats why its called specific. | text | null |
L_1034 | specific heat | T_4884 | The Table 1.1 compares the specific heat of four different substances. Metals such as iron have low specific heat. It doesnt take much energy to raise their temperature. Thats why a metal spoon heats up quickly when placed in a cup of hot coffee. Sand also has a relatively low specific heat. Water, on the other hand, has a very high specific heat. It takes a lot more energy to increase the temperature of water than sand. This explains why the sand on a beach gets hot while the water stays cool. Differences in the specific heat of water and land even affect climate. Substance iron sand wood Specific Heat (joules) 0.45 0.67 1.76 Q: Metal cooking pots and pans often have wooden handles. Can you explain why? A: Wood has a higher specific heat than metal, so it takes more energy to heat a wooden handle than a metal handle. As a result, a wooden handle would heat up more slowly and be less likely to burn your hand when you touch it. | text | null |
L_1037 | states of matter | T_4892 | The photo above represents water in three common states of matter. States of matter are different phases in which any given type of matter can exist. There are actually four well-known states of matter: solid, liquid, gas, and plasma. Plasma isnt represented in the iceberg photo, but the other three states of matter are. The iceberg itself consists of water in the solid state, and the lake consists of water in the liquid state. Q: Where is water in the gaseous state in the above photo? A: You cant see the gaseous water, but its there. It exists as water vapor in the air. Q: Water is one of the few substances that commonly exist on Earth in more than one state. Many other substances typically exist only in the solid, liquid, or gaseous state. Can you think of examples of matter that usually exists in just one of these three states? A: Just look around you and you will see many examples of matter that usually exists in the solid state. They include soil, rock, wood, metal, glass, and plastic. Examples of matter that usually exist in the liquid state include cooking oil, gasoline, and mercury, which is the only metal that commonly exists as a liquid. Examples of matter that usually exists in the gaseous state include oxygen and nitrogen, which are the chief gases in Earths atmosphere. | text | null |
L_1037 | states of matter | T_4893 | A given kind of matter has the same chemical makeup and the same chemical properties regardless of its state. Thats because state of matter is a physical property. As a result, when matter changes state, it doesnt become a different kind of substance. For example, water is still water whether it exists as ice, liquid water, or water vapor. | text | null |
L_1037 | states of matter | T_4894 | The most common states of matter on Earth are solids, liquids, and gases. How do these states of matter differ? Their properties are contrasted in the Figure 1.1. Click image to the left or use the URL below. URL: Properties of matter in different states. Q: The Figure 1.2 shows that a liquid takes the shape of its container. How could you demonstrate this? A: You could put the same volume of liquid in containers with different shapes. This is illustrated below with a beaker (left) and a graduated cylinder (right). The shape of the liquid in the beaker is short and wide like the beaker, while the shape of the liquid in the graduated cylinder is tall and narrow like that container, but each container holds the same volume of liquid. Q: How could you show that a gas spreads out to take the volume as well as the shape of its container? A: You could pump air into a bicycle tire. The tire would become firm all over as air molecules spread out to take the shape of the tire and also to occupy the entire volume of the tire. | text | null |
L_1037 | states of matter | T_4894 | The most common states of matter on Earth are solids, liquids, and gases. How do these states of matter differ? Their properties are contrasted in the Figure 1.1. Click image to the left or use the URL below. URL: Properties of matter in different states. Q: The Figure 1.2 shows that a liquid takes the shape of its container. How could you demonstrate this? A: You could put the same volume of liquid in containers with different shapes. This is illustrated below with a beaker (left) and a graduated cylinder (right). The shape of the liquid in the beaker is short and wide like the beaker, while the shape of the liquid in the graduated cylinder is tall and narrow like that container, but each container holds the same volume of liquid. Q: How could you show that a gas spreads out to take the volume as well as the shape of its container? A: You could pump air into a bicycle tire. The tire would become firm all over as air molecules spread out to take the shape of the tire and also to occupy the entire volume of the tire. | text | null |
L_1039 | sublimation | T_4898 | Solid carbon dioxide is also called dry ice. Thats because when it gets warmer and changes state, it doesnt change to a liquid by melting. Instead, it changes directly to a gas without going through the liquid state. The process in which a solid changes directly to a gas is called sublimation. It occurs when energy is added to a solid such as dry ice. Click image to the left or use the URL below. URL: Q: Alyssas mom put some mothballs in her closet in the spring to keep moths away from her wool clothes. By autumn, the mothballs were much smaller. What happened to them? A: Mothballs are made of naphthalene, a substance that undergoes sublimation at room temperature. The solid mothballs slowly changed to a gas during the summer months, explaining why they were much smaller by autumn. | text | null |
L_1039 | sublimation | T_4899 | Snow and ice may also undergo sublimation under certain conditions. This is most likely to happen where there is intense sunlight, very cold temperatures, and dry winds. These conditions are often found on mountain peaks. As snow sublimates, it gradually shrinks without any runoff of liquid water. Click image to the left or use the URL below. URL: | text | null |
L_1047 | temperature | T_4917 | No doubt you already have a good idea of what temperature is. You might say that its how warm or cool something feels. In physics, temperature is defined as the average kinetic energy of the particles of matter. When particles of matter move more quickly, they have more kinetic energy, so their temperature is higher. With a higher temperature, matter feels warmer. When particles move more slowly, they have less kinetic energy on average, so their temperature is lower. With a lower temperature, matter feels cooler. | text | null |
L_1047 | temperature | T_4918 | Many thermometers measure temperature with a liquid that expands when it gets warmer and contracts when it gets cooler. Look at the common household thermometer pictured in the Figure 1.1. The red liquid rises or falls in the glass tube as the temperature changes. Temperature is read off the scale at the height of the liquid in the tube. Q: Why does the liquid in the thermometer expand and contract when temperature changes? A: When the temperature is higher, particles of the liquid have greater kinetic energy, so they move about more and spread apart. This causes the liquid to expand. The opposite happens when the temperature is lower and particles of liquid have less kinetic energy. The particles move less and crowd closer together, causing the liquid to contract. | text | null |
L_1047 | temperature | T_4919 | The thermometer pictured in the Figure 1.1 measures temperature on two different scales: Celsius (C) and Fahrenheit (F). Although some scientists use the Celsius scale, the SI scale for measuring temperature is the Kelvin scale. If you live in the U.S., you are probably most familiar with the Fahrenheit scale. The Table 1.1 compares all three temperature scales. Each scale uses as reference points the freezing and boiling points of water. Notice that temperatures on the Kelvin scale are not given in degrees ( ). Scale Kelvin Celsius Fahrenheit Freezing Point of Water 273 K 0 C 32 F Boiling Point of Water 373 K 100 C 212 F Because all three temperature scales are frequently used, its useful to know how to convert temperatures from one scale to another. Its easy to convert temperatures between the Kelvin and Celsius scales. Each 1-degree change on the Kelvin scale is equal to a 1-degree change on the Celsius scale. Therefore, to convert a temperature from Celsius to Kelvin, just add 273 to the Celsius temperature. For example, 10 C equals 283 Kelvin. Q: How would you convert a temperature from Kelvin to Celsius? A: You would subtract 273 from the Kelvin temperature. For example, a temperature of 300 Kevin equals 27 C. Converting between Celsius and Fahrenheit is more complicated. The following conversion factors can be used: Celsius Fahrenheit: ( C 1.8) + 32 = F Fahrenheit Celsius: ( F - 32) 1.8 = C 3. Assume that the temperature outside is 293 Kelvin but youre familiar only with the Fahrenheit scale. Do you need to wear a hat and gloves when you go outside? To find out, convert the Kelvin temperature to Fahrenheit. (Hint: Convert the Kelvin temperature to Celsius first.) | text | null |
L_0001 | the nature of science | T_0001 | The scientific method is a set of steps that help us to answer questions. When we use logical steps and control the number of things that can be changed, we get better answers. As we test our ideas, we may come up with more questions. The basic sequence of steps followed in the scientific method is illustrated in Figure 1.1. | text | null |
L_0001 | the nature of science | T_0002 | Asking a question is one really good way to begin to learn about the natural world. You might have seen something that makes you curious. You might want to know what to change to produce a better result. Lets say a farmer is having an erosion problem. She wants to keep more soil on her farm. The farmer learns that a farming method called no-till farming allows farmers to plant seeds without plowing the land. She wonders if planting seeds without plowing will reduce the erosion problem and help keep more soil on her farmland. Her question is this: Will using the no-till method of farming help me to lose less soil on my farm? (Figure 1.2). | text | null |
L_0001 | the nature of science | T_0002 | Asking a question is one really good way to begin to learn about the natural world. You might have seen something that makes you curious. You might want to know what to change to produce a better result. Lets say a farmer is having an erosion problem. She wants to keep more soil on her farm. The farmer learns that a farming method called no-till farming allows farmers to plant seeds without plowing the land. She wonders if planting seeds without plowing will reduce the erosion problem and help keep more soil on her farmland. Her question is this: Will using the no-till method of farming help me to lose less soil on my farm? (Figure 1.2). | text | null |
L_0001 | the nature of science | T_0003 | Before she begins, the farmer needs to learn more about this farming method. She can look up information in books and magazines in the library. She may also search the Internet. A good way for her to learn is to talk to people who have tried this way of farming. She can use all of this information to figure out how she is going to test her question about no-till farming. Farming machines are shown in the Figure 1.3. | text | null |
L_0001 | the nature of science | T_0004 | After doing the research, the farmer will try to answer the question. She might think, If I dont plow my fields, I will lose less soil than if I do plow the fields. Plowing disrupts the soil and breaks up roots that help hold soil in place. This answer to her question is a hypothesis. A hypothesis is a reasonable explanation. A hypothesis can be tested. It may be the right answer, it may be a wrong answer, but it must be testable. Once she has a hypothesis, the next step is to do experiments to test the hypothesis. A hypothesis can be proved or disproved by testing. If a hypothesis is repeatedly tested and shown to be true, then scientists call it a theory. | text | null |
L_0001 | the nature of science | T_0005 | When we design experiments, we choose just one thing to change. The thing we change is called the independent variable. In the example, the farmer chooses two fields and then changes only one thing between them. She changes how she plows her fields. One field will be tilled and one will not. Everything else will be the same on both fields: the type of crop she grows, the amount of water and fertilizer that she uses, and the slope of the fields she plants on. The fields should be facing the same direction to get about the same amount of sunlight. These are the experimental controls. If the farmer only changes how she plows her fields, she can see the impact of the one change. After the experiment is complete, scientists then measure the result. The farmer measures how much soil is lost from each field. This is the dependent variable. How much soil is lost from each field depends on the plowing method. | text | null |
L_0001 | the nature of science | T_0006 | During an experiment, a scientist collects data. The data might be measurements, like the farmer is taking in Figure labeled. Labeling helps the scientist to know what each number represents. A scientist may also write descriptions of what happened during the experiment. At the end of the experiment the scientist studies the data. The scientist may create a graph or drawing to show the data. If the scientist can picture the data the results may be easier to understand. Then it is easier to draw logical conclusions. Even if the scientist is really careful it is possible to make a mistake. One kind of mistake is with the equipment. For example, an electronic balance may always measure one gram high. To fix this, the balance should be adjusted. If it cant be adjusted, each measurement should be corrected. A mistake can come if a measurement is hard to make. For example, the scientist may stop a stopwatch too soon or too late. To fix this, the scientist should run the experiment many times and make many measurements. The average of the measurements will be the accurate answer. Sometimes the result from one experiment is very different from the other results. If one data point is really different, it may be thrown out. It is likely a mistake was made in that experiment. | text | null |
L_0001 | the nature of science | T_0007 | The scientist must next form a conclusion. The scientist must study all of the data. What statement best explains the data? Did the experiment prove the hypothesis? Sometimes an experiment shows that a hypothesis is correct. Other times the data disproves the hypothesis. Sometimes its not possible to tell. If there is no conclusion, the scientist may test the hypothesis again. This time he will use some different experiments. No matter what the experiment shows the scientist has learned something. Even a disproved hypothesis can lead to new questions. The farmer grows crops on the two fields for a season. She finds that 2.2 times as much soil was lost on the plowed field as compared to the unplowed field. She concludes that her hypothesis was correct. The farmer also notices some other differences in the two plots. The plants in the no-till plots are taller. The soil moisture seems higher. She decides to repeat the experiment. This time she will measure soil moisture, plant growth, and the total amount of water the plants consume. From now on she will use no-till methods of farming. She will also research other factors that may reduce soil erosion. | text | null |
L_0001 | the nature of science | T_0008 | When scientists have the data and conclusions, they write a paper. They publish their paper in a scientific journal. A journal is a magazine for the scientists who are interested in a certain field. Before the paper is printed, other scientists look at it to try to find mistakes. They see if the conclusions follow from the data. This is called peer review. If the paper is sound it is printed in the journal. Other papers are published on the same topic in the journal. The evidence for or against a hypothesis is discussed by many scientists. Sometimes a hypothesis is repeatedly shown to be true and never shown to be false. The hypothesis then becomes a theory. Sometimes people say they have a theory when what they have is a hypothesis. In science, a theory has been repeatedly shown to be true. A theory is supported by many observations. However, a theory may be disproved if conflicting data is discovered. Many important theories have been shown to be true by many observations and experiments and are extremely unlikely to be disproved. These include the theory of plate tectonics and the theory of evolution. | text | null |
L_0001 | the nature of science | T_0009 | Scientists use models to help them understand and explain ideas. Models explain objects or systems in a more simple way. Models often only show only a part of a system. The real situation is more complicated. Models help scientists to make predictions about complex systems. Some models are something that you can see or touch. Other types of models use an idea or numbers. Each type is useful in certain ways. Scientists create models with computers. Computers can handle enormous amounts of data. This can more accu- rately represent the real situation. For example, Earths climate depends on an enormous number of factors. Climate models can predict how climate will change as certain gases are added to the atmosphere. To test how good a model is, scientists might start a test run at a time in the past. If the model can predict the present it is probably a good model. It is more likely to be accurate when predicting the future. | text | null |
L_0001 | the nature of science | T_0010 | A physical model is a representation of something using objects. It can be three-dimensional, like a globe. It can also be a two-dimensional drawing or diagram. Models are usually smaller and simpler than the real object. They most likely leave out some parts, but contain the important parts. In a good model the parts are made or drawn to scale. Physical models allow us to see, feel and move their parts. This allows us to better understand the real system. An example of a physical model is a drawing of the layers of Earth (Figure 1.5). A drawing helps us to understand the structure of the planet. Yet there are many differences between a drawing and the real thing. The size of a model is much smaller, for example. A drawing also doesnt give good idea of how substances move. Arrows showing the direction the material moves can help. A physical model is very useful but it cant explain the real Earth perfectly. | text | null |
L_0001 | the nature of science | T_0011 | Some models are based on an idea that helps scientists explain something. A good idea explains all the known facts. An example is how Earth got its Moon. A Mars-sized planet hit Earth and rocky material broke off of both bodies (Figure 1.6). This material orbited Earth and then came together to form the Moon. This is a model of something that happened billions of years ago. It brings together many facts known from our studies of the Moons surface. It accounts for the chemical makeup of rocks from the Moon, Earth, and meteorites. The physical properties of Earth and Moon figure in as well. Not all known data fits this model, but much does. There is also more information that we simply dont yet know. | text | null |
L_0001 | the nature of science | T_0012 | Models may use formulas or equations to describe something. Sometimes math may be the only way to describe it. For example, equations help scientists to explain what happened in the early days of the universe. The universe formed so long ago that math is the only way to describe it. A climate model includes lots of numbers, including temperature readings, ice density, snowfall levels, and humidity. These numbers are put into equations to make a model. The results are used to predict future climate. For example, if there are more clouds, does global temperature go up or down? Models are not perfect because they are simple versions of the real situation. Even so, these models are very useful to scientists. These days, models of complex things are made on computers. | text | null |
L_0001 | the nature of science | T_0013 | Accidents happen from time to time in everyday life. Since science involves an adventure into the unknown, it is natural that accidents can happen. Therefore, we must be careful and use proper equipment to prevent accidents (Figure 1.7). We must also be sure to treat any injury or accident appropriately. | text | null |
L_0001 | the nature of science | T_0014 | If you work in the science lab, you may come across dangerous materials or situations. Sharp objects, chemicals, heat, and electricity are all used at times in science laboratories. With proper protection and precautions, almost all accidents can be prevented (Figure 1.8). If an accident happens, it can be dealt with appropriately. Below is a list of safety guidelines to follow when doing labs: Follow directions at all times. A science lab is not a play area. Be sure to obey all safety guidelines given in lab instructions or by the lab supervisor. Be sure to use the correct amount of each material. Tie back long hair. Wear closed shoes with flat heels. Shirts should have no hanging sleeves, hoods, or drawstrings. Use gloves, goggles, or safety aprons as instructed. Be very careful when you use sharp or pointed objects, such as knives. Clean up broken glass quickly with a dust pan and broom. Never touch broken glass with your bare hands. Never eat or drink in the science lab. Table tops and counters could have dangerous substances on them. Keep your work area neat and clean. A messy work area can lead to spills and breakage. Completely clean materials like test tubes and beakers. Leftover substances could interact with other sub- stances in future experiments. If you are using flames or heat plates, be careful when you reach. Be sure your arms and hair are kept far away from heat sources. Use electrical appliances and burners as instructed. Know how to use an eye wash station, fire blanket, fire extinguisher, and first aid kit. Alert the lab supervisor if anything unusual occurs. Fill out an accident report if someone is hurt. The lab supervisor must know if any materials are damaged or discarded. | text | null |
L_0001 | the nature of science | T_0015 | Many Earth science investigations are conducted in the field (Figure 1.9). Field work needs some additional precautions: Be sure to wear appropriate clothing. Hiking requires boots, long pants, and protection from the Sun, for example. Bring sufficient supplies like food and water, even for a short trip. Dehydration can occur rapidly. Take along first aid supplies. Let others know where you are going, what you will be doing, and when you will be returning. Take a map with you if you dont know the area and leave a copy of the map with someone at home. Try to have access to emergency services and some way to communicate. Beware that cell phones may not have coverage in all locations. Be sure that you are accompanied by a person familiar with the area or is familiar with field work. | text | null |
L_0005 | erosion and deposition by wind | T_0045 | Dust storms like the one in Figure 10.20 are more common in dry climates. The soil is dried out and dusty. Plants may be few and far between. Dry, bare soil is more easily blown away by the wind than wetter soil or soil held in place by plant roots. | text | null |
L_0005 | erosion and deposition by wind | T_0046 | Like flowing water, wind picks up and transports particles. Wind carries particles of different sizes in the same ways that water carries them. You can see this in Figure 10.21. Tiny particles, such as clay and silt, move by suspension. They hang in the air, sometimes for days. They may be carried great distances and rise high above the ground. Larger particles, such as sand, move by saltation. The wind blows them in short hops. They stay close to the ground. Particles larger than sand move by traction. The wind rolls or pushes them over the surface. They stay on the ground. | text | null |
L_0005 | erosion and deposition by wind | T_0047 | Did you ever see workers sandblasting a building to clean it? Sand is blown onto the surface to scour away dirt and debris. Wind-blown sand has the same effect. It scours and polishes rocks and other surfaces. Wind-blown sand may carve rocks into interesting shapes. You can see an example in Figure 10.22. This form of erosion is called abrasion. It occurs any time rough sediments are blown or dragged over surfaces. Can you think of other ways abrasion might occur? | text | null |
L_0005 | erosion and deposition by wind | T_0048 | Like water, when wind slows down it drops the sediment its carrying. This often happens when the wind has to move over or around an obstacle. A rock or tree may cause wind to slow down. As the wind slows, it deposits the largest particles first. Different types of deposits form depending on the size of the particles deposited. | text | null |
L_0005 | erosion and deposition by wind | T_0049 | When the wind deposits sand, it forms small hills of sand. These hills are called sand dunes. For sand dunes to form, there must be plenty of sand and wind. Sand dunes are found mainly in deserts and on beaches. You can see examples of sand dunes in Figure 10.23. | text | null |
L_0005 | erosion and deposition by wind | T_0049 | When the wind deposits sand, it forms small hills of sand. These hills are called sand dunes. For sand dunes to form, there must be plenty of sand and wind. Sand dunes are found mainly in deserts and on beaches. You can see examples of sand dunes in Figure 10.23. | text | null |
L_0005 | erosion and deposition by wind | T_0050 | What causes a sand dune to form? It starts with an obstacle, such as a rock. The obstacle causes the wind to slow down. The wind then drops some of its sand. As more sand is deposited, the dune gets bigger. The dune becomes the obstacle that slows the wind and causes it to drop its sand. The hill takes on the typical shape of a sand dune, shown in Figure 10.24. | text | null |
L_0005 | erosion and deposition by wind | T_0051 | Once a sand dune forms, it may slowly migrate over the land. The wind moves grains of sand up the gently sloping side of the dune. This is done by saltation. When the sand grains reach the top of the dune, they slip down the steeper side. The grains are pulled by gravity. The constant movement of sand up and over the dune causes the dune to move along the ground. It always moves in the same direction that the wind usually blows. Can you explain why? | text | null |
L_0005 | erosion and deposition by wind | T_0052 | When the wind drops fine particles of silt and clay, it forms deposits called loess. Loess deposits form vertical cliffs. Loess can become a thick, rich soil. Thats why loess deposits are used for farming in many parts of the world. You can see an example of loess in Figure 10.25. | text | null |
L_0005 | erosion and deposition by wind | T_0053 | Its very important to control wind erosion of soil. Good soil is a precious resource that takes a long time to form. Covering soil with plants is one way to reduce wind erosion. Plants and their roots help hold the soil in place. They also help the soil retain water so it is less likely to blow away. Planting rows of trees around fields is another way to reduce wind erosion. The trees slow down the wind, so it doesnt cause as much erosion. Fences like the one in Figure 10.26 serve the same purpose. The fence in the figure is preventing erosion and migration of sand dunes on a beach. | text | null |
L_0013 | history of earths life forms | T_0113 | There are over 1 million species of plants and animals living on Earth today. Scientists think that there are millions more that have not yet been discovered. | text | null |
L_0013 | history of earths life forms | T_0114 | Each organism has the ability to survive in a specific environment. Dry desert environments are difficult to live in. Desert plants have special stems and leaves to conserve water. Animals have other ways to live in the desert. The Namib Desert receives only 1.5 inches of rainfall each year. The Namib Desert beetle lives there. How do the beetles get enough water to survive? Early morning fog deposits water droplets. The droplets collect on a beetles wings and back. The beetle tilts its rear end up. When the droplet is heavy enough, it slides forward. It lands in the beetles mouth. There are many other environments that need unique approaches for survival (Figure 12.10). | text | null |
L_0013 | history of earths life forms | T_0115 | Organisms must be able to get food and avoid being food. Hummingbirds have long, thin beaks that help them drink nectar from flowers. Some flowers are tubular to fit hummingbird beaks. The battle between needing food and being food plays out in the drama between lions and zebras. When a herd of zebras senses a lion, the animals run away. The zebras dark stripes confuse the lions. It becomes hard for them to focus on just one zebra. The zebras may get away. But lions are swift and agile. A lion may be able to get a zebra, maybe one thats old or sick. | text | null |
L_0013 | history of earths life forms | T_0116 | Every organism is different from every other organism. Every organisms genes are different, too. | text | null |
L_0013 | history of earths life forms | T_0117 | There are variations in the traits of a population. For example, there are lots of variations in the color of human hair. Hair can be blonde, brown, black, or even red. Hair color is a trait determined by genes. | text | null |
L_0013 | history of earths life forms | T_0118 | At some point, the variation probably came from a mutation. A mutation is a random change in an organisms genes. Mutations are natural. Some are harmful, but many are neutral. If the trait from the mutation is beneficial, that organism may have a better chance to survive. An organism that survives is likely to have offspring. If it does, it may pass the mutation on to its offspring. The offspring may be more likely to survive. | text | null |
L_0013 | history of earths life forms | T_0119 | Some of the characteristics an organism has may help it survive. These characteristics are called adaptations. Some adaptations are better than others. Adaptations develop this way. Think about a population of oak trees. Imagine that a fungus has arrived from Asia to North America. Most of the North American are killed by the fungus. But a few oak trees have a mutation that allows them to survive the fungus. Those oak trees are better adapted to the new environment than the others. Those trees have a better chance of surviving. They will probably reproduce. The trees may pass on the favorable mutation to their offspring. The other trees will die. Eventually, the population of oak trees will change. Most of the trees will have the trait to survive the fungus. This is an adaptation. Over time, traits that help an organism survive become more common. Traits that hinder survival eventually disappear. | text | null |
L_0013 | history of earths life forms | T_0120 | Adaptations in a species add up. If the environment is stable, the species wont change. But if the environment is changing, the species will need to adapt. Many adaptations may be necessary. In time, the species may change a lot. The descendants will be very different from their ancestors. They may even become a new species. This process is called evolution. Evolution happens as a species changes over time. Organisms alive today evolved from earlier life forms. We can learn about this from fossils. For example, horse fossils from 60 million years ago are very different from modern horses. Ancient horses were much smaller than they are today (Figure 12.12). The horses teeth and hooves have also changed. The horses evolved because of changes in their environment. | text | null |
L_0013 | history of earths life forms | T_0121 | Most of the organisms that once lived on Earth are now extinct. Earths environment has changed many times. Many organisms could not adapt to the changes. They died out. The organisms that did survive passed traits on to their offspring. The changes added up, eventually producing the species we see today. We study fossils to see the organisms that lived at certain times. We can see how those organisms changed with time. We can see how they evolved. | text | null |
L_0013 | history of earths life forms | T_0122 | The Phanerozoic Eon is divided into three eras the Paleozoic, the Mesozoic, and the Cenozoic (Table 12.1). They span from about 540 million years ago to the present. We live now in the Cenozoic Era. Earths climate changed numerous times during the Phanerozoic Eon. Just before the beginning of the Phanerozoic Eon, much of the Earth was covered with glaciers. As the Phanerozoic Eon began, the climate became a warm and humid tropical climate. During the Phanerozoic, Earths climate has gone through at least 4 major cycles between times of cold glaciers and times of warm tropical seas. Some organisms survived environmental changes in the climate; others became extinct when the climate changed beyond their capacity to cope with it. | text | null |
L_0013 | history of earths life forms | T_0123 | The warm, humid climate of the early Cambrian allowed life to expand and diversify. This brought the Cambrian Explosion. Life exploded both in diversity and in quantity! By the beginning of the Paleozoic, organisms had developed shells. Shells could hold their soft tissues together. They could protect the organisms from predators and from drying out. Some organisms evolved external skeletons, called exoskeletons. Organisms with hard parts also make good fossils. Fossils from the Cambrian are much more abundant than fossils from the Precambrian. There was much more diversity, so complex ecosystems could develop (Figure 12.14). All of this was in the seas. | text | null |
L_0013 | history of earths life forms | T_0124 | Paleozoic life was most diverse in the oceans. Paleozoic seas were full of worms, snails, clams, trilobites, sponges, and brachiopods. Organisms with shells were common. The first fish were simple, armored, jawless fish. Fish have internal skeletons. Some, like sharks, skates, and rays, have skeletons of cartilage. More advanced fish have skeletons of bones. Fish evolved jaws and many other adaptations for ocean life. Figure 12.13 shows some of the diversity of Earths oceans. | text | null |
L_0013 | history of earths life forms | T_0125 | An organism that lives in water is supported by the water. It does not need strong support structures. It also does not need to be protected against drying out. This is not true of land. Moving from the seas to land required many adaptations. Algae had covered moist land areas for millions of years. By about 450 million years ago, plants began to appear on land. Once there were land plants, animals had a source of food and shelter. To move to land, animals needed strong skeletons. They needed protection from drying out. They needed to be able to breathe air. Eventually they had skeletons, lungs and the other the adaptations they needed moved onto the land. One group of fish evolved into amphibians. Insects and spiders were already land dwellers by the time amphibians appeared. | text | null |
L_0013 | history of earths life forms | T_0125 | An organism that lives in water is supported by the water. It does not need strong support structures. It also does not need to be protected against drying out. This is not true of land. Moving from the seas to land required many adaptations. Algae had covered moist land areas for millions of years. By about 450 million years ago, plants began to appear on land. Once there were land plants, animals had a source of food and shelter. To move to land, animals needed strong skeletons. They needed protection from drying out. They needed to be able to breathe air. Eventually they had skeletons, lungs and the other the adaptations they needed moved onto the land. One group of fish evolved into amphibians. Insects and spiders were already land dwellers by the time amphibians appeared. | text | null |
L_0013 | history of earths life forms | T_0126 | The Mesozoic Era is the age of reptiles. Mostly we think of it as the age of dinosaurs. Earth was populated by an enormous diversity of reptiles. Some were small and some were tremendously large. Some were peaceful plant eaters. Some were extremely frightening meat eaters. Some dinosaurs developed protection, such as horns, spikes, tail clubs, and shielding plates. These adaptations were defense against active predators. Most dinosaurs lived on land. Still, pterosaurs flew the skies. Plesiosaurs and ichthyosaurs swam in the oceans (Figure 12.15). Feathered dinosaurs gave rise to birds. | text | null |
L_0013 | history of earths life forms | T_0127 | The Cenozoic Era is the age of mammals. The Cenozoic began with the extinction of every land creature larger than a dog. The most famous victims were the dinosaurs. Mammals have the ability to regulate body temperature. This is an advantage, as Earths climate went through sudden and dramatic changes. Mastodons, saber tooth tigers, hoofed mammals, whales, primates and eventually humans all lived during the Cenozoic Era (Figure 12.16). Table 12.1 shows some of the life forms that developed during the Phanerozoic Eon. Life gradually became more diverse and new species appeared. Most modern organisms evolved from species that are now extinct. Era Cenozoic Millions of Years Ago 0.2 (200,000 years ago) 35 Mesozoic 130 150 200 Major Forms of Life First humans First grasses; grasslands begin to dominate the land First plants with flowers First birds on Earth First mammals on Earth Paleozoic 300 360 400 475 First reptiles on Earth First amphibians on Earth First insects on Earth First plants and fungi begin growing on land First fish on Earth 500 | text | null |
L_0013 | history of earths life forms | T_0128 | The eras of the Phanerozoic Eon are separated by mass extinctions. During these events, large numbers of organisms became extinct very rapidly. There have been several extinctions in the Phanerozoic but two stand out more than the others. | text | null |
L_0013 | history of earths life forms | T_0129 | Between the Paleozoic Era and the Mesozoic Era was the largest mass extinction known. At the end of the Permian, nearly 95% of all marine species died off. In addition, 70% of land species became extinct. No one knows the cause of this extinction. Some scientists blame an asteroid impact. Other scientists think it was a gigantic volcanic eruption. | text | null |
L_0013 | history of earths life forms | T_0130 | The most famous mass extinction was 65 million years ago. Between the Mesozoic Era and the Cenozoic Era, about 50% of all animal species died off. This mass extinction is when the dinosaurs became extinct. Most scientists think that the extinction was caused by a giant meteorite that struck Earth. The impact heated the atmosphere until it became as hot as a kitchen oven. Animals roasted. Dust flew into the atmosphere and blocked sunlight for a year or more. This caused a deep freeze and ended photosynthesis. Sulfur from the impact mixed with water in the atmosphere. The result was acid rain. The rain dissolved the shells of the tiny marine plankton that form the base of the food chain. With little food being produced, animals starved. | text | null |
L_0024 | air movement | T_0240 | Air movement takes place in the troposphere. This is the lowest layer of the atmosphere. Air moves because of differences in heating. These differences create convection currents and winds. Figure 15.19 shows how this happens. Air in the troposphere is warmer near the ground. The warm air rises because it is light. The light, rising air creates an area of low air pressure at the surface. The rising air cools as it reaches the top of the troposphere. The air gets denser, so it sinks to the surface. The sinking, heavy air creates an area of high air pressure near the ground. Air always flows from an area of higher pressure to an area of lower pressure. Air flowing over Earths surface is called wind. The greater the difference in pressure, the stronger the wind blows. | text | null |
L_0024 | air movement | T_0241 | Local winds are winds that blow over a limited area. They are influenced by local geography. Nearness to an ocean, lake or mountain range can affect local winds. Some examples are found below. | text | null |
L_0024 | air movement | T_0242 | Ocean water is slower to warm up and cool down than land. So the sea surface is cooler than the land in the daytime. It is also cooler than the land in the summer. The opposite is also true. The water stays warmer than the land during the night and the winter. These differences in heating cause local winds known as land and sea breezes. Land and sea breezes are illustrated in Figure 15.20. A sea breeze blows from sea to land during the day or in summer. Thats when air over the land is warmer than air over the water. The warm air rises. Cool air from over the water flows in to take its place. A land breeze blows from land to sea during the night or in winter. Thats when air over the water is warmer than air over the land. The warm air rises. Cool air from the land flows out to take its place. | text | null |
L_0024 | air movement | T_0243 | Monsoons are like land and sea breezes, but on a larger scale. They occur because of seasonal changes in the temperature of land and water. In the winter, they blow from land to water. In the summer, they blow from water to land. In regions that experience monsoons, the seawater offshore is extremely warm. The hot air absorbs a lot of the moisture and carries it over the land. Summer monsoons bring heavy rains on land. Monsoons occur in several places around the globe. The most important monsoon in the world is in southern Asia, as shown in Figure 15.21. These monsoons are important because they carry water to the many people who live there. | text | null |
L_0024 | air movement | T_0244 | Global winds are winds that occur in belts that go all around the planet. You can see them in Figure 15.22. Like local winds, global winds are caused by unequal heating of the atmosphere. | text | null |
L_0024 | air movement | T_0245 | Earth is hottest at the equator and gets cooler toward the poles. The differences in heating create huge convection currents in the troposphere. At the equator, for example, warm air rises up to the tropopause. It cant rise any higher, so it flows north or south. By the time the moving air reaches 30 N or S latitude, it has cooled. The cool air sinks to the surface. Then it flows over the surface back to the equator. Other global winds occur in much the same way. There are three enormous convection cells north of the equator and three south of the equator. | text | null |
L_0024 | air movement | T_0246 | Earth is spinning as air moves over its surface. This causes the Coriolis effect. Winds blow on a diagonal over the surface, instead of due north or south. From which direction do the northern trade winds blow? Without Coriolis Effect the global winds would blow north to south or south to north. But Coriolis makes them blow northeast to southwest or the reverse in the Northern Hemisphere. The winds blow northwest to southeast or the reverse in the southern hemisphere. The wind belts have names. The Trade Winds are nearest the equator. The next belt is the westerlies. Finally are the polar easterlies. The names are the same in both hemispheres. | text | null |
L_0024 | air movement | T_0247 | Jet streams are fast-moving air currents high in the troposphere. They are also the result of unequal heating of the atmosphere. Jet streams circle the planet, mainly from west to east. The strongest jet streams are the polar jets. The northern polar jet is shown in Figure 15.23. | text | null |
L_0026 | changing weather | T_0262 | An air mass is a large body of air that has about the same conditions throughout. For example, an air mass might have cold dry air. Another air mass might have warm moist air. The conditions in an air mass depend on where the air mass formed. | text | null |
L_0026 | changing weather | T_0263 | Most air masses form over polar or tropical regions. They may form over continents or oceans. Air masses are moist if they form over oceans. They are dry if they form over continents. Air masses that form over oceans are called maritime air masses. Those that form over continents are called continental air masses. Figure 16.6 shows air masses that form over or near North America. An air mass takes on the conditions of the area where it forms. For example, a continental polar air mass has cold dry air. A maritime polar air mass has cold moist air. Which air masses have warm moist air? Where do they form? | text | null |
L_0026 | changing weather | T_0264 | When a new air mass goes over a region it brings its characteristics to the region. This may change the areas temperature and humidity. Moving air masses cause the weather to change when they contact different conditions. For example, a warm air mass moving over cold ground may cause an inversion. Why do air masses move? Winds and jet streams push them along. Cold air masses tend to move toward the equator. Warm air masses tend to move toward the poles. Coriolis effect causes them to move on a diagonal. Many air masses move toward the northeast over the U.S. This is the same direction that global winds blow. | text | null |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.