Three Holes, part 2

Hopefully, you spent quite a bit of time thinking about last week's experiment, and more importantly, performing the experiment to see if you were correct. If not, before you read any more, GO TRY IT! If you don't, you are missing out on the actual fun of scientific investigation. This week, you will need:

- the same materials that we used in part 1.
- 3 more bottles
- some wooden blocks or other things to change the height of the bottles

If you did try it, you probably got results similar to what you see in the photo below.

If you did try it, you found that the water stream from the middle hole hit at the greatest distance from the bottle. Why? To understand that, we need to look at the variables involved with each of the three streams.

Variable? What is that? It is something that can change from one test to another. If we think of the three holes as three different tests, then the variables are the things that change from one to another.

The first variable is the water pressure, and that varies according to the depth of the water. The deeper the water, the greater the pressure. That means that the top hole will have the least water pressure, and the bottom hole will have the greatest water pressure. Then why didn't the bottom stream go the farthest? Because there is another variable involved.

What else is different for each stream, besides the water pressure? The distance that they have to fall to hit the surface! If that distance is too short, the stream when it could still travel much further from the bottle. The top stream has a longer distance to fall, giving it a longer time to move away from the bottle. The bottom stream has the shortest distance to fall, so it has the least time to move away from the bottle.

Looking at the three streams, the bottom one has the most water pressure, but not very far to fall before it hits the surface. The top stream has the least water pressure, but a long way to go before it hits. The middle stream has more pressure than the top, and more distance to fall than the bottom. That combination lets it hit the farthest from the bottle.

Is there a way that we can compare those variables? Easy! All we have to do is to control one of those variables.

Which will go farther?

You could control the water pressure by using three bottles that each had a hole at the same depth. By placing the bottles on top of blocks, you could arrange them so that the three streams were at different heights. With the same pressure for each, the highest stream would go farther, since it has the longest time to travel away from the bottle before it hits the surface.

Which will go farther this time?

You could control the distance the water has to fall by using three bottles again, but this time, make a hole near the bottom of one, near the middle of the second, and near the top of the third. Then place them on blocks so that the three streams are all the same distance from the surface. This time, the stream with the most water pressure (nearest the bottom of the bottle) will go farther.

From there, you can gradually change the height of the blocks until all three bottles were the same height. That would bring you back to where we started, with the middle stream reaching the farthest. With careful testing, you would probably find that the maximum distance would not be at exactly the middle of the bottle, since one variable may make a larger difference than the other. If one is causing more difference, which do you think it is? You'll have to try it yourself to find out.

Have a wonder-filled week.

Three Holes
This week's experiment will give you some good practice at thinking scientifically. The experiment itself is very simple, but as with many simple things, the more you think about it, the more you will see. To try this, you will need: - a two liter soft drink bottle - pliers - a sharp nail - water First you need to empty the two liter bottle. I highly recommend using the soda to experiment with making the perfect ice cream float. Once the bottle is empty, rinse it and remove the plastic label if it has one.
We want to make three holes in the plastic bottle, each at a different depth. Holding the nail with the pliers, make a small hole about one inch up from the bottom of the bottle. I found that twisting the nail back and forth as you push makes it easier to start the hole. You want the hole to be round and as smooth as possible. Be careful not to tear the plastic (or your skin!) Once you make the hole, wiggle the nail around a bit to help make the hole round.
After you make the first hole, make the second about half way up the bottle, and slightly to one side. You want all three holes to be as close to the same size as possible, and you do not want the holes to be directly above each other. The third hole should be about an inch or so below the point where the top of the bottle starts to narrow, and again a little to one side. The photo on the right shows approximate locations.
Place the bottle in the sink, under the faucet. Fill the bottle with water, and leave the water flowing just enough to keep the bottle full as the water flows out of the three holes. We want to compare how far each stream of water goes, which is why we did not want one hole directly above another. We want to be able to see the three streams easily. Now you should understand why we are working in the sink, to keep from making a mess.

Before you actually try this experiment, take some time to think about it. Once the bottle is full, water will be flowing out of all three holes. If you measured how far each stream of water moved away from the bottle before it hit the bottom of the sink, which stream of water would hit the farthest away? Which stream would hit the closest? Why? Keep in mind that there may be more than one thing to consider in how far the water reaches.

Once you have spent enough time thinking to have a good idea of what will happen, turn on the water and try it yourself. Next week, we will look at the results, and figure out why it worked the way it did.

Have a wonder-filled week!

Go to Part 2.

Link to Part 1

Link to Part 2

The answer to Part 2, and a fun "science trick."

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Link to Part 1

Link to Part 3

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Link to Part 2

Link to Part 3

What really keeps the water inside this inverted glass?

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There are many things that will float on water: pieces of wood, wax, Styrofoam, and many other things. They float because they are less dense than the water. Now for the question. Can water float on water? Is there a way to make water less dense?

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Pull downwards on the string, and use science to cause it to break either above or below the book.

How quick are you?

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Which will go out first, the tall candle or the short one?

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The answer to the last video's challenge.

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Try this easy way to visualize how gravity differs from planet to planet.

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Make a diver that will rise and fall at your command, if you know the science.

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This week's experiment comes from a recent question, wanting to know whether gravity is a law or a theory. That question brings up so many more questions that I thought it would be fun to explore. To try this, you will need:

- an object to drop.

OK, pick an object that will not break, dent the floor, cause a mess, or get either of us in trouble. Hold it out in front of you and release it. What happens? It falls, of course. The gravitational attraction between the Earth and the object pulls it towards the ground. But, when we do this experiment, should we be talking about the Law of Gravity or the Theory of Gravity?

Actually, we should be talking about both. To understand why, we need to understand the scientific meaning of the words "law" and "theory."

In the language of science, the word "law" describes an analytic statement. It gives us a formula that tells us what things will do. For example, Newton's Law of Universal Gravitation tells us that "Every point mass attracts every single point mass by a force pointing along the line intersecting both points. The force is directly proportional to the product of the two masses and inversely proportional to the square of the distance between the point masses." That formula will let us calculate the gravitational pull between the Earth and the object you dropped, between the Sun and Mars, or between me and a bowl of ice cream.

We can use Newton's Law of Universal Gravitation to calculate how strong the gravitational pull is between the Earth and the object you dropped, which would let us calculate its acceleration as it falls, how long it will take to hit the ground, how fast it would be going at impact, how much energy it will take to pick it up again, etc.

While the law lets us calculate quite a bit about what happens, notice that it does not tell us anything about why it happens. That is what theories are for. In the language of science, the word "theory" is used to describe an explanation of why and how things happen. For gravity, we use Einstein's Theory of General Relativity to explain why things fall.

A theory starts as one or more hypotheses, untested ideas about why something happens. For example, I might propose a hypothesis that the object that you released fell because it was pulled by the Earth's magnetic field. Once we started testing, it would not take long to find out that my hypothesis was not supported by the evidence. Non-magnetic objects fall at the same rate as magnetic objects. Because it was not supported by the evidence, my hypothesis does not gain the status of being a theory. To become a scientific theory, an idea must be thoroughly tested, and must be an accurate and predictive description of the natural world.

While laws rarely change, theories change frequently as new evidence is discovered. Instead of being discarded due to new evidence, theories are often revised to include the new evidence in their explanation. The Theory of General Relativity has adapted as new technologies and new evidence have expanded our view of the universe.

So when we are scientifically discussing gravity, we can talk about the law that describes the attraction between two objects, and we can also talk about the theory that describes why the objects attract each other.

Have a wonder-filled week.

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