Re: What physics is behind the 'stomp rocket'

It's always good to incorporate your toys into your teaching.  Don't let
that bleed too far, though, I've turned calculators into toys. . .

Here are a couple of ideas for turning toy rockets into science.
1. Send it up and note the travel time.  If it's ten seconds, then at five
seconds, it was at the apex (top) right?  Well, everyone knows that the
accleration due to gravity is 32ft/sec^2, so maybe you can calculate how
high it went this way.

2. Have someone stand (say) 30 meters from the rocket.  When it gets
launched, have them find the angle they have to look up to see its apex.
You can use some basic trig to find it height OR measure how far the
shadow goes along the ground when the sun it a given angle off 90.

3. Demonstrate  the concept of work.  Work is force times distance.  If
you drop a ten pound ball from ten feet, the rocket goes (say) 20 ft up.
Double the distance you drop the ball from and it goes higher.  Now do the
same thing with a 20 pound ball (or whatever is appropriate.)

4.  Here's one that will suprise them, but it might be hard to pull off.
Try to set it up so that the rocket goes in a arc and another object falls
from the same height.  The time it takes for the rocket to fall will match
the time it takes for the object to cover the same distance.  For
instance, if you shoot a bullet perfectly sideways, it will be in the air
exactly the same amount of time a marble dropped straight down from the
same height would be.  This is because gravity is a "conservative force"
that only really acts in one direction (i.e. down).

5. The whole reason the rocket goes anywhere is because of gas pressure.
You make the pressure of the gas inside the rocket much higher without
increasing the volume.  THe gas wants to leave the chamber.  The gas
leaving the chamber is what pushes the rocket up.  You can use this to
introduce PV=nRT.  Normal air is at about 1atm, so when the gas inside the
rocket gets a chance to escape to an area of low pressure, it will.  YOu
could get the same effect if you heated the gas, but that's harder to
control.  Maybe you could have them calculate how much hotter the gas
would have to be to get the same effect.  That may be a bit advanced. . .

6. At the time of launch, the kinetic energy of the rocket is a maximum
and the potential energy a minimum.  At the apex, you have the reverse
situation.  When the rocket hits the ground, it should be travelling at
"exactly" the same speed as the instant it left.  If you can figure out
how much kinetic energy is in the landing rocket, you know how much energy
was in the rocket at the apex.  From there, you could find height or
launch speed or whatever.

7. Conservation of energy.  The energy that launched the rocket came from
your foot.  That energy came from ATP in your body, which came from food,
which came from plants (eventually) who got their energy from the sun.  So
the rocket was launched by energy from the sun.  When they ask where the
sun got its energy, tell them to ask their astronomy prof. :)

8. The rocket could symbolise an electron in photosynthesis.  When it gets
energy from the sun (your foot) it gets excited and moves to a higher
orbital.  As it falls, it sheds the energy it had (here, heating the air
around it) and intialising the
production of ATP.

Well, I hope that gave you some ideas.  Thanks for the question!  It was
fun answering!