Aquajet science

By: Rick Newlands

What’s an aquajet?

• ‘Aqua’ means ‘water’.

• An aquajet is a rocket that uses water.

• You fill a plastic bottle 1/3rd full of water, then pump the bottle up with air.

• Then you let it go and it flies away!

• The water jets out of the bottle.

Paisley Rocketeer’s SocietyMr Stewart of the Paisley Rocketeers taught us how to make aquajets.

Forces

• Aquajets work by making a force.

• A force is a push or pull that tries to move something.

• In Star Wars, the 'force' is a mysterious power that Jedi Knights have to push, pull, or throw things without touching them.

• If your family loses their housekeys and can't get into the house, dad may have to 'force' the front door, which means kicking the door down.

• A 'force 10' wind is a howling gale with the strength to blow the roof off a house.

The push-back force• Imagine that you and a friend are both on skateboards,

and you push your friend away …

• You’ll find that you get pushed backwards yourself!

The reaction force• The famous scientist Isaac Newton called the push force that you

make the action force. The push-back force that then magically occurs and pushes you backwards, he called the reaction force.

• So forces always come in pairs: the action and the reaction.

• With rockets, the reaction force is called thrust.

Aquajet rockets• Aquajet rockets work by pushing water away from them. The pushing

away is the action force.

• The reaction force that then occurs pushes on the front of the aquajet, moving it forwards.

• Notice that all the pushing goes on inside the rocket, so it doesn’t matter what’s outside. It could be empty outer Space outside but the rocket will still work.

How it works: squashed air• Air can be squashed just like squashing a big spring.

• To make the action and reaction forces happen to the aquajet, then first we’ve got to fill the aquajet bottle with lots of very squashed air.

• As the air gets larger, it gets squashed!

Launching the aquajet• Now that we’ve squashed the poor old air, we can then open the

aquajet bottle and the air will un-squash and push the water out at high speed.

• So it’s the squashed air that makes the action force.• Launch the aquajet!

• The air pushes on the water, but also pushes on the front of the bottle, which moves the aquajet forwards.

Big rockets• Big rockets burn fuel to keep making hot, squashed gas.

• Instead of pushing water away, the new hot gas pushes away old hot gas that was made a few moments earlier. This is the action force.

• The new gas also pushes on the front of the bottle: this is the reaction force that pushes the rocket forwards.

Finish the aquajet• We add a nosecone to the front of the aquajet to let it cut through the

air more easily, so that it flies further.

• Then we add some weight to the nose, and also add fins at the back. These keep the aquajet flying nose-first like a dart. (Without the fins and noseweight, the aquajet would just tumble through the air and wouldn’t fly very far.)

• We make the nosecone soft and squashy just in case the aquajet lands on your head!