The other part of the water rocket system is the rocket itself. Usually the rocket is made from a 2-liter soda pop bottle. Before launch, the bottle is filled with some amount of water, which acts as the "propellant" for the launch. Since water is about times heavier than air, the expelled water produces more thrust than compressed air alone.
The base of the bottle is only slightly larger than the launch tube. When the rocket is placed on the launch tube, the body tube becomes a closed pressure vessel. The pressure inside the body tube equals the pressure produced by the air pump. Fins are attached to the bottom of the body tube to provide stability during the flight.
Set up the launch pad and pump firmly on the ground, with the launcher facing away from the group and towards an open space. All observers should be at least 3—5m away from the launcher. Pour —mL of water into the rocket. Lift the handle on the launch pad and carefully fit the pop bottle onto the nozzle. Ensure that the bottle is locked in. Be sure not to go past 40 psi 5—6 bike pumps as greater pressure can rupture the bottle rocket. Start a countdown! Tips on using the launcher A good seal is required to pressurize the bottle.
If you see a spray of water as you pump, the seal is too loose. Bottles become weakened from launching and landing. Although a new bottle can withstand more pressure, never pressurize a bottle above 40 psi. Retire water rockets after 10 flights or sooner if you suspect damage. Extensions Try different shaped bottles or putting different shaped fins on the bottle to make it fly straighter.
Divide the class into groups of 2 or 3 and allow each to design their own rocket, adding fins, a nose cone, and any other features they think will help the rocket fly further or straighter. Test the rockets to see what designs fly best. Experiment with the angles at which you launch the rocket.
Which angle makes the rocket travel furthest? Experiment with the amount of water you add—what happens if you half fill the bottle with water?
How far can you get a bottle to go? Check that your launchpad allows the bottle to fly cleanly away. You may need to try a few methods depending on your pump and the shape of your bottle. This design is a basic one to show how the principle works. Using just the friction of a cork to hold in the air and water means the pressure can't get very high.
And most bottles aren't a great shape for smooth flight. There are many other, more advanced, rocket designs. Some people compete in national competitions. Explore the Internet for inspiration and see how you can improve your rocket.
There are a few suggested links top right on this page. Rockets work by ejecting something out of the back and a so-called 'reaction force' then pushes the body of the rocket forward. Here, water and air are shoved out the back. The water is heavier so that's what gives the bottle the main kick forwards.
The energy to force the water out is stored as air pressure inside the bottle. You supply the energy as you pump air into the bottle. The air pressure inside builds up and pushes on the water. But friction holds the cork in place and that pushes back on the water, so for a while nothing moves. Once the friction force can no longer contain the pressure, the cork is shoved out and the pressure then acts on the water to eject it from the bottle.
Compared to the bottle, the water is heavy. So pushing water out at a moderate speed backwards gives the bottle a lot of forward speed. Perhaps you have heard of Newton's laws of motion. Isaac Newton was the 17th century British scientist whose ideas about gravity and other forces transformed science. Oh, and an apple may have fallen on his head. Every action has an equal and opposite reaction. The water moves one way and the bottle goes the opposite way. The same amount of force can accelerate a heavy object slowly or a light object more quickly.
The water is much heavier than the empty plastic bottle. Search term:. Read more. This page is best viewed in an up-to-date web browser with style sheets CSS enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets CSS if you are able to do so.
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