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Work With Air & Water

Feeling pushed and pulled in all directions? This activity will put you in control

Australian Curriculum links

  • Science > Physical Sciences > Year 4 > ACSSU076
  • Science > Physical Sciences > Year 7 > ACSSU117

You’ll need

  • 2 plastic syringes
  • Flexible plastic tubing
  • Cardboard
  • Scissors
  • Tape

What to do

Pull the plunger of a syringe back so it is full of air.

Attach this syringe to some plastic tubing.

Attach another syringe to the other end of the tubing, but this time leave the plunger in the syringe.

Push on the extended plunger. What happens to the plunger at the other end of the tubing?

Repeat the experiment, but this time fill the plastic tubing and the first syringe with water. Is it easier or harder to move the second syringe?

Design a small object out of cardboard so that part of the object can be moved using the movement of air through the tubing to the other syringe. For example, you could put the body of a turtle on the syringe, and its head and neck on the plunger.

What’s happening?

As the air is forced out of one syringe, it is pushed along the tubing and into the other one. There will be a delay between pushing the plunger on one end and the plunger at the other end moving, because air can be compressed (or squashed). When you push the plunger in, the air is compressed, increasing the pressure of the air in the tubing. After a while the pressure gets high enough that it can push the plunger out at the other end of the tubing.

When you have the plunger and the tube filled with water there is no delay in the movement. This is because water cannot be compressed. As soon as you push the plunger, the water pushes out the other plunger. There will only be a delay if you still have air in your system. Try pushing down both plungers at once. You can move them both a little way when you have air in the tube but not at all when the tube is full of water.

Real world links

The term ‘hydraulic’ refers to something that is moved, operated or affected by water. Car brakes, wing flaps on aeroplanes and heavy machinery (such as dump trucks and excavators) all use hydraulic systems to move, like the water-powered syringes used in this activity, but on a much larger scale.

The term ‘pneumatic’ can be used to refer to a machine, which moves using compressed air. Air brakes on busses and jackhammers are examples of pneumatic machines.