BALLOON ROCKET

You Will Need:

• A long skinny balloon

• Scotch tape

• Clothes pin, or binder clip (a type of paper clip)

• Light cardboard (a shirt stiffener, or the back of a pad)

MAKING YOUR ROCKET

Cut three, or four triangles out of the cardboard to make fins for the rocket.  They should be large enough that they will stick out from the sides of the rocket three to four inches.

Inflate the balloon, but do not tie it.  Instead, clamp off the end of the balloon with the clothes pin, so that the air cannot escape.

Attach the cardboard fins to the rocket with tape, equidistant around the circumfrance of the balloon, near the end of the balloon that you inflate.  Be careful to keep the fins running parallel to the length of the balloon.  If they are crooked, the rocket will not fly straight.

EXPERIMENTING WITH THE ROCKET

Take your rocket outside (for safety, don't try flying it inside).  Place the rocket on the ground, with the clothes pin facing down, and the other end of the rocket facing up.  Make sure you are out of the flight path of the rocket, and remove the clothes pin.

How did it fly?  What could you do to make it fly better, higher, straighter?

Now, try changing the fins on your rocket.  Will it fly better with larger, or smaller fins?  Does it make a difference how many fins you put on the rocket?  Does it make a difference in how much air you put in the balloon?

EXPLAINING HOW IT WORKS

Rocket propulsion works by pressure.  When you blow up the balloon, you make the air pressure inside the balloon greater than the air pressure outside the balloon.  This air pressure is the fuel for your rocket.  Then, when you removed the clothes pin, you allowed the air inside the balloon to escape.  It tries to escape because the air inside the balloon is trying to equalize its pressure (become the same) with the air outside the balloon.

As the air escapes from the balloon, it presses against the ground, and the air outside the balloon.  According to Newton's third law, as the air coming out of the balloon presses against the air outside the balloon, the air outside presses back.  This makes the balloon rocket move.

The fins on the rocket act to steer it.  As the rocket moves through the air, the fins "slice" through the air.  Since the air coming out of the balloon is pushing the rocket, the fins will try and go through the air in the easiest path possible.  The easiest path is always straight.

Depending on the size of your fins, and how straight they are, the rocket may, or may not fly really straight.  Generally speaking, larger fins will cause the rocket to fly straighter.  However, if the fins are too large, they get wobbly, and will make the rocket go crooked.  Try different size fins, or even putting the fins on crooked to see the difference it makes in your rocket's flight.

Real rockets actually have very small fins.  However, the rocket engine (the part where the air comes out) can be tilted slightly.  This allows the astronauts to steer the rocket by changing which way the "push" is.