A column of water presses down on its base. Each cubic centimeter adds another gram of mass changing water pressure on the base. We saw how that works last week.
When the siphon moved water from one jar to another, the water ran slower as the jars were closer in height or the water level went down in the jar.
If you put a hole in a can, any water in the can will run out. What if there is more than one hole in the can? How will this affect how the water runs out of the can?
Question: How does changing water pressure affect how water flows?
It is possible to use a nail if there is a tight board inside the can. Drilling a hole is much easier and makes a better hole.
The line of holes is supposed to be straight. Mine wavered a little as the drill slipped a bit on the can.
Put pieces of tape over the holes in the cans. Be sure these are tight.
The piece of tape needs to be tight over the hole. The ends are left loose for easy grabbing.
The can set well on the upside down jar. I didn’t get it put back exactly the same every time but couldn’t be too far off or the can would fall off. I filled the can to the rim each time.
I measured from the jar each time as the centimeters started a little out on the ruler accounting for the overhang of the can.
Masking tape will not stick to a wet can. Again the ends are loose for easy grabbing. Each part over a hole is rubbed down tightly.
Set the can back on the prop can and fill it with water to the same place as before.
If each tape is on tightly on a dry surface, the pieces will hold even through refilling.
This can behaved differently as the third hole stream went as far as the bottom hole in the first can.
It helps to hold the top of the can steady while pulling off the piece of tape.
Opening one hole on the bottom let the stream of water go out 26 cm. It stayed that far for a time as the water level dropped then slowly moved closer to the can until it finally dribbled out as the water level reached the hole.
Each time the stream of water is the longest at first and ends when the water level is the same as the hole.
Nickels work well for marking the distances. They are easy to see. They are heavy enough the water stream can’t wash them away.
For the first can, compare how the water stream with one hole open acts with how the three act with all the holes open.
The three streams went out a shorter distance than for a single hole. The water level l was the same over all three but the water had more than one way to go so less went out each hole.
For the first can, is the water pressure the same for all the holes? Why do you think so?
Is the rate of changing water pressure the same for all the holes? Why do you think so?
For the second can, is the water pressure the same for all the holes? Why do you think so?
Does where a hole is placed in a container affect how water empties out of the container?
All four distances were a little less than for single holes.
For the second can, compare how the water stream for the third hole acts with only that hole open to when all the holes are open.
Describe the changing water pressure as a can empties out.
Use the changing water pressure to explain how the water streams act as a can empties.
Do you think changing the sizes of the holes would change how the can empties?
Do you think making the holes different sizes would change how the can empties?
My holes were a little high around the can. I put the tapes pieces over the three holes, set the can up and filled it with water. One tape dripped a little.
I steadied the can with one hand and pulled one piece of tape off. The stream of water went out. I marked it. It stayed going that far for a long time then gradually moved in until it was a dribble down the side of the can.
It was hard to dry the can until I got a towel. Then the tape went over all three holes. This time I steadied the can and jerked the tape off. Three streams of water shot out.
I marked the distance for one stream but the streams moved in faster than the single stream did. The three were soon dribbled down the side of the can.
For the single stream the distance was 26 cm. The distance with all three streams going was 23 cm.
The three streams acted much the same as the single stream except for being a little shorter and losing distance much faster. Since all the holes were the same distance up from the bottom of the can and the water was as deep over all the holes, they had the same water pressure on them. That made the rate of changing water pressure the same for all of them because the water level dropped the same over all of them.
Having the holes lined up from top to bottom of the can made the water act differently for each hole. The top hole water stream went the shortest distance, only 16 cm. The water stream shortened to a dribble very quickly.
The hole next down put out a longer stream, 24.5 cm. This stream lasted longer too.
The third hole had an even longer stream, 26 cm, and lasted longer too.
The fourth hole had the longest stream, 29 cm, and lasted the longest too.
The water level dropped very quickly with all four holes open. This made it hard to mark all four streams at one test.
The water streams acted the same as for the three holes. Changing water pressure caused the streams to get shorter until they dribbled as the water level dropped to the hole level.
These holes had different water pressure behind them as the water column over each was different.
When all four holes were opened up, the streams of water were shorter. The changing water pressure made the streams change distance quickly. I had to refill the can to get all of them marked.
Making all the holes larger would let the water out faster. I think the streams would be shorter too because making the hole at the end of a hose makes the water go farther.
If the holes were different sizes, the water would go out the larger holes faster so the changing water pressure would make the streams get shorter faster.
This entry was posted in Outside Project, Uncategorized and tagged changing water pressure, science, science activity, water pressure on August 6, 2016 by [email protected].