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.