This rocket uses pressurized water as a propellant!
Watch The Video:
- Conservation of Momentum
Have you ever seen a cannon fire before? As the projectile leaves the barrel of the gun, the gun recoils from the blast. That effect (the recoil) is the same effect that enables rockets to lift off.
Simply put, a rocket has two basic elements: a body, and fuel, which is stored in the body. The fuel has mass, so as it is blown out the bottom of the rocket, it causes the body to recoil upwards. If the body is forced hard enough upwards, it can lift off - up off the ground, up into the sky, and (in the case of space rockets) up into outer space! To get the strongest upwards lift, you basically need to do two things:
- blow a large mass of fuel out the bottom, and
- blow that fuel out very quickly.
Oh yeah - and it's easier launch a light rocket, so the less mass the body has, the better. You can sum up these ideas nicely with the idea of "momentum". The momentum (p) of an object is its mass (m) times it's velocity (v):
p = mv
So the more momentum the fuel has as it's being ejected, the faster (and higher) the rocket will lift off.
The rocket in this demo is a pop bottle filled part-way with water. The mouth is plugged with a rubber stopper, and a bicycle pump and inflater pin are used to pressurize the bottle. When the air pressure builds up enough, it forces the plug and the water out the mouth of the bottle, and the recoil fires the bottle into the air.
- Bicycle pump
- Stopper with an inflater pin inserted through the end
- 2-L pop bottle
- Stand to hold the bottle
- Take a 2-L bottle, and fill it 1/3 full with of water
- Place a stopper that has an inflater pin in the mouth of the bottle
- Place the water-filled bottle into a holding container (launch pad)
- Connect the stopper to a tire pump
- Go into a wide open area and push a few times on the air pump to increase the pressure within the bottle
- Pump until the bottle shoots off into the air!
- Tips: When placing the rubber stopper in the water-filled bottle, make sure it's in tight, and when pumping the bottle, be sure to stand away from the rocket and not lean over it while pumping.