Launch a powerful rocket using water pressure
Suitable For
Grade 8
Difficulty
3
Time Required
<2 Days
Supervision
Required
What’s it about?
A rocket is a very powerful machine which obtains ‘thrust’ or ‘propulsion’ by ejecting a jet of fast moving fluid exhaust from its engine. Rockets are most often launched vertically to try and overcome the force of gravity and travel from the earth out to space. There are many different ways in which a rocket can be propelled, for instance by: air pressure, burning fuel or using water pressure as in the following experiment:
Topics covered
Rocket, Water pressure
What will I need?
- 2L PLASTIC SODA BOTTLE
- WINE CORK
- BICYCLE PUMP (FOOT TYPE)
- NEEDLE USED TO INFLATE FOOTBALL
- 2x BRICKS
- TAP WATER
- ADULT HELPER
Procedure (Method)
A rocket is a very powerful machine which obtains ‘thrust’ or ‘propulsion’ by ejecting a jet of fast moving fluid exhaust from its engine. Rockets are most often launched vertically to try and overcome the force of gravity and travel from the earth out to space. There are many different ways in which a rocket can be propelled, for instance by: air pressure, burning fuel or using water pressure as in the following experiment:
- Push a long hollow needle, used for inflating a football, through the centre of a thick wine cork so that the needle opening is visible on the bottom of the cork. The cork should fit very snugly into the mouth of a 2L plastic soda bottle. If you cannot find a wide enough cork to fit snugly, wind some sticky tape around the cork to make it wider and fit more tightly. (The tighter the fit, the better will be your rocket launch result. Make sure, however, that it is loose enough to pop out when pressure is applied.)
- Attach the inflation needle to a bicycle pump. (A strong pump, preferably a foot pump, would work best for this experiment.)
- In a large outside open area, build a launch pad for your rocket out of two or more bricks. The plastic bottle should be able to ‘lean’ against the bricks in a vertical position with the mouth of the bottle facing down to the ground.
- Now, fill an empty 2L plastic soda bottle with water about three quarters full and place the cork which is attached to the pump, into the mouth of the ‘bottle rocket’.
- Position the plastic bottle vertically on the brick ‘launch pad’, with the cork pressed against the ground.
- Start pumping air into the bottle with the bicycle pump. You will see air bubbles coming out of the inflation needle and into the water if your rocket is working correctly. Continue to pump until the cork ‘pops’ out and the rocket is launched into the air!
Caution: The rocket in the above experiment is extremely powerful and can be very dangerous. This experiment should only be performed outdoors and in a large open area. Always point the rocket away from people, including yourself. This rocket can cause injury if improperly used.
How does it work?
This science experiment works according to Newton’s ‘Law of reaction’. The force or ‘action’ of the compressed air forcing the water backwards sets up an equal force or ‘reaction’ for the bottle going forwards. As the water in the soda bottle is released, the water will spurt out of the mouth of the bottle against the ground and your ‘bottle rocket’ will shoot up in the air. Increasing the air pressure will add distance to your rocket’s flight to a point, but there is a limit to its effect as air will start to leak out through the cork. There is also a limit to the optimum amount of water to be used to launch the rocket. When the amount of water is increased, the weight that the rocket must carry during its flight is also increased so more water does not necessary mean a higher flight.
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