Have you ever heard the expression "it's not rocket science"? Well, this week's activity is rocket science. This week, we will look at the basic principal behind how rockets work.
You will need:
A balloon
Fishing line, preferably on a reel (or it will become tangled)
Several Straws
Sticky tape
Scissors
A couple of helpers.
What to do
First, we will reinforce the straw (make it stronger), so it won't bend.
Take three or four straws.
Using the scissors, cut along the length of the straws, so they each have a split down the side.
Slide the split straws inside an intact straw.
Thread the fishing line through the straw.
Have one person hold the end of the fishing line or tie it to something.
Unroll several metres of fishing line and have another volunteer hold it so the line is held taunt.
Slide the straw to one end.
Blow up the balloon, but don't tie it off.
Sticky tape the balloon to the straw so it points towards the other end of the fishing line.
Use a couple of pieces of sticky tape.
It can help if your helper holds the neck of the balloon for you.
Let go of the balloon and it will rocket along the fishing line to the other end.
What's going on?
Many years ago, a scientist named Isaac Newton realised that when an object applies a force onto another object, the other object pushes back with an equal force, in the opposite direction.
When you let go of the balloon, the balloon pushes the air out the neck of the balloon. As it does, the air pushes on the balloon with equal force in the opposite direction, so the balloon is pushed along the fishing line. The air comes out of the balloon faster than the balloon is pushed along, because the air is much lighter than the balloon.
All rockets work by using the same principle. In a rocket, fuel is burned in a combustion chamber, which is open at one end. As the fuel burns, it produces hot gases, which rush out the open end of the chamber. Since the gases are being pushed in one direction by the rocket, the rocket is pushed in the opposite direction with equal force.
When a rocket pushes hot gas backwards (blue arrow) the rocket feels an equal force forwards (green arrow)
In case you are wondering, we reinforced the straw to stop it bending. I find this activity works best when you use a couple of pieces of sticky tape to attach the straw to the balloon, because it stops the balloon wobbling around. However, if you use an ordinary straw, then as the balloon shrinks, it will bend the straw in the middle. When this happens, the fishing line jams and it comes to a sudden stop. By reinforcing the straw, we stop it bending in the middle.
Slide the split straws into an intact straw. This will make a straw that doesn't bend easily.
Thread the fishing line through the straw. Sticky tape an inflated balloon to the straw.
Thread the fishing line through the straw. Sticky tape an inflated balloon to the straw.
