# OS10 Water Balloon Pressure

Water shot out of a hole in a can in an arc to the ground. The greater the water pressure behind the hole, the longer the arc. As the pressure fell, the arc shrank. Shouldn’t a hole in a water balloon act the same way?

Question: What happens to water coming out of a hole in a water balloon?

Materials:

Balloon

Pin

Water faucet in a large sink or hose

Block to set the water balloon on

Procedure:

Blow the balloon up about half way

Hold the neck closed and push on the balloon

How does the air behave?

It is easier to put a single hole in a partially blown up balloon. If the balloon is blown up too much, it will break.

Make a pin hole about half way down the balloon

Let the air go out of the hole

How does the balloon change as the air goes out?

Slide the neck of the balloon over the end of the faucet or hose [wetting it first makes this easier]

Even if the mouth of the balloon is tight on the faucet, hold it on as you put water in the balloon.

Place the block so the balloon will sit on it as it fills up

Turn the water on slowly to fill the balloon

How does the water come out through the hole?

What happens to the hole?

Turn the water off when the balloon is about two thirds full

Observe how the water and the balloon act as the water goes out of the water balloon

Warning: Do NOT take the balloon off the faucet until almost all of the water is out of it‼!

Observations:

How does air behave

When you push on an air filled balloon

When the air comes out of a hole in the balloon

Describe how water acts as you fill the water balloon

Like the water from the hole in the can, water arcs out of the hole in the balloon

Describe what happens to the hole

Describe what happens as the water balloon empties

Describe what happens to the balloon as it fills and empties

Conclusions:

Why does putting pressure on one part of an air filled balloon make another part bulge?

What happens to the balloon as you put pressure inside of it?

Why does the water arc get thicker as more water goes into the balloon?

The balloon stretches out and has elastic energy adding pressure to the water in the balloon making the water arc much bigger than the one from the can.

Compare the water arcs from the cans to the one from the balloon.

Why does the water arc from the balloon last so long?

What I Found Out:

I had some big round balloons. It was easy to blow one up just a little and poke a pin hole in it.

The balloon fit on the faucet in my bathroom sink tightly. I turned the water on a little.

For a few seconds water dripped out of the hole and ran down the balloon. After that the water arced out of the balloon. The balloon got bigger and so did the arc. Then both stopped changing.

I turned the water on a little harder. The balloon got a little bigger. The arc had more water in it but didn’t seem any bigger.

A balloon stretches as it gets bigger. A letter written on a balloon gets bigger as a balloon gets bigger. The hole got bigger so more water could get out.

I turned the water on a little more. The balloon got bigger slowly. The arc straightened out and had more water in it.

Taking the mouth of the balloon off the faucet before the balloon is empty lets the water form a geyser out of the mouth. This is only fun if you are outside on a hot day.

My sink was far too small. When the balloon got about eight inches across, the arc shot out over the sink and onto the floor.

When the water ran out of the can, the arc quickly shrank. The arc of water out of the balloon stayed up for a long time.

When I was done, I took the balloon off the faucet. Water shot up out of the mouth of the balloon like a geyser.

Only air and gravity put pressure on the water arcing out of the can. The balloon put pressure on the water inside of it making the arc large for a longer time and shooting the water out of the mouth when I took it off the faucet.

# OS9 Changing Water Pressure

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?

Materials:

2 very large juice cans with the top removed or soda bottles with the tops cut off

1 soup can or jar to set the large cans or bottles on

Large tray [not needed if you do this outside]

Drill with a 1/8 inch bit [Help to drill some holes in the cans]

Ruler

Tape

4 Nickels

Procedure:

Drill three holes 0.5 cm from the bottom of one juice can or soda bottle spaced around the can

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.

Use the ruler to make a line down one side of the other can or soda bottle

Mark a point 0.5cm from the bottom, 5.5 cm up, 10.5 cm and 15.5 cm

The line of holes is supposed to be straight. Mine wavered a little as the drill slipped a bit on the can.

Drill holes at each mark

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.

Put the can with three holes on the small can in the tray, a bathtub or ground outside

Fill the can with water to the top or a mark so you can fill the can the same each time

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.

Pull off one piece of tape and put a nickel where the water first hits the tray or ground

Measure how far the water went from the can

I measured from the jar each time as the centimeters started a little out on the ruler accounting for the overhang of the can.

Describe how the water stream acts as the can empties

Take off all the tape from the holes and dry the outside of the can thoroughly

Put one piece of tape over all three holes

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.

Pull the tape off quickly and put a nickel where one of the streams of water hits the tray or ground

Observe how the three streams of water act as the can empties out

Measure how far the water went from the can

Set this can aside and put pieces of tape over the holes

Put the other can on the prop can

If each tape is on tightly on a dry surface, the pieces will hold even through refilling.

Fill the can with water

Pull off the top tape piece and put a nickel where the water first hits the tray or ground

Measure how far the water went

Dry the outside of the can and replace the piece of tape

Fill the can

Pull the tape from the second hole down and put a nickel where the water first hits

Measure how far the water goes

Dry the outside of the can and replace the piece of tape

Fill the can with water

Pull the tape from the third hole down and put a nickel where the water first hits

This can behaved differently as the third hole stream went as far as the bottom hole in the first can.

Measure how far the water goes

Dry the outside of the can and replace the piece of tape

Fill the can with water

Pull the bottom piece of tape and put a nickel where the water first hits

Measure how far the water goes

Remove the pieces of tape and dry the outside of the can

It helps to hold the top of the can steady while pulling off the piece of tape.

Put one piece of tape covering all the holes

Set the can on the prop can

Fill the can with water

Pull the tape off quickly and place nickels where each stream of water hits the ground

[You may have to do this more than once to mark all the streams of water.]

Observe how the streams of water act

Measure how far the water goes for each hole

Observations:

1st can:

Distance the water goes with one hole open

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.

How the water acts as the can empties

Distance the water goes with all three holes open

How the water acts as the can empties

2nd can:

Distance for top hole

How the water stream acts as the can empties

Distance for top hole with all holes open

Distance for second hole

Each time the stream of water is the longest at first and ends when the water level is the same as the hole.

How the water stream acts as the can empties

Distance for second hole with all holes open

Distance for third hole

How the water stream acts as the can empties

Distance for third hole with all holes open

Nickels work well for marking the distances. They are easy to see. They are heavy enough the water stream can’t wash them away.

Distance for fourth hole

How the water stream acts as the can empties

Distance for fourth hole with all holes open

How the water acts as the can empties

Conclusions:

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?

Is the rate of changing 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?

[You can try this and compare your ideas with what happens.]

What I Found Out:

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.

# OS8 Water Pressure

Perhaps you noticed the water flowing through the siphons slowed down as the top jar emptied out. Why would it do this?

Is this slowing related to less water in the jar so the mass is less making the water pressure on the siphon less?

When people go down to the bottom of the ocean, they go in small vehicles called bathyscaphes with very thick windows. Why is the glass so thick?

Question: What is water pressure?

Materials:

Scale

Thin plastic water bottle, empty

Water

Procedure:

Place the empty water bottle on the scale to mass it

Massing the empty bottle is important as you can then subtract this mass to find the mass of the water you add later on.

Take the bottle off the scale and pour 1 cm water in the bottle

Mass the bottle and water

Take the bottle off the scale

Pour 1 cm water in the bottle

The first centimeter is in the bottle. It distributes this mass over the bottom putting pressure on the scale.

Mass the bottle

Repeat this until the bottle is full or the scale can not have more mass on it

Observations:

Masses of bottle and water

Conclusions:

What happens to the mass of the bottle and water each time you add more water?

The bottle is filling up. Still all the mass of the water rests on the bottom of the bottle sitting on the scale.

If you were a bug standing on the bottom of the bottle, how much mass would be resting on your back when the first water landed in the bottle?

How much mass would be resting on your back when all the water is in the bottle?

Pressure is how much mass is resting on a certain area. As you add water mass to the bottle, what is happening to the water pressure on the bottom?

Water has a mass of 1 g for each cubic centimeter. If you were standing under a column of water a meter (100 cm) tall, how much mass or water pressure would be resting on you?

What if that column of water was 10 meters (1000 cm) tall?

Why are the windows of the bathyscaphes so thick?

What I Found Out:

Every time I added water to my bottle, the mass increased. Only 58.8 g of water would sit on my buggy back when the first centimeter of water arrived in my bottle. I’m glad I’m not a bug on the bottom of the bottle when the bottle was full because I would have 510.0 g of water sitting on my back.

The bottle is now full. All the mass is still resting on the bottom of the bottle giving that amount of pressure on the scale.

Since the area the water was resting on did not increase, the water column kept getting taller and heavier putting more pressure on that same area.

A column of water 100 cm tall would put 100 g of mass or pressure on my shoulder. But a column 1000 cm tall would put 1000 g of mass on my shoulder.

Bathyscaphes go to the bottom of the ocean, miles down. A mile is about 1.5 km or 1500 m or 150,000 cm which is 150,000 g or 150 kg of mass. [A kilogram is about 2.2 pounds so that is 330 pounds.] This would break a regular window. The thick glass is harder to break with the pressure.