# Height of a Water Rocket.

Q:
How do you measure how high your air pressured water rocket goes?
- Daison k. Lyons (age 13)
A:
Dear Daison,

The easiest way to measure the height that a rocket goes (or the height of just about anything) is to use some really cool math called Trigonometry. Trigonometry (or "trig" for short) is a bit like geometry since it allows us to figure stuff out about triangles. If you have not learned about this in school yet, don’t worry...all you need is a calculator that has the function "tan" on it and you are all set. I will insert a picture here to make this easier to explain:

Ask a friend to launch your rocket while you stand over to one side. Before you start measure how far from the launch-pad you are. Lets call this distance D.

Now shoot the rocket straight up into the air, and point at the rocket with your arm the whole time. You need to estimate the angle that your arm makes with the ground when the rocket is at the top of its flight. Recall that 0 degrees is pointing parallel to the ground (like before the rocket is shot) and 90 degrees is straight up. You will probably estimate something in between.

To find the height of the rocket, take the distance D and multiply it by the "tan" of the angle you guessed. For example if you guessed 60 degrees and D is 20 meters, the height of the rocket is

(20 meters)*tan(60 degrees) = 35 meters

See if you can figure out a better way than guessing to get the angle of the rocket (maybe using a protractor).

MS

(published on 10/22/2007)

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