Level: Elementary to Middle School
Time involvement: 10-20 minutes.
Materials: Required: large open outdoor space and an air compressor. This soda bottle rocket is always in popular demand (weather permitting). The “launcher” can be built from scratch or purchased on the Internet. A 2 liter soda bottle is required although a smaller one can be substituted. Depending on the pressure used an altitude of 100 feet is possible. Filling the bottle with about one third water gives the optimum results. The demonstration works with no water but the altitude gained will be less. Be forewarned: this is an outdoor hand-held launch set-up. The person holding the launcher should wear a raincoat or “play” clothes. You may/will get wet! Wind drift can easily require a ladder to make a recovery necessary from a rooftop. Launching into the wind or on the upwind side of the field will help control the landing zone. Because it uses only compressed air there is no danger of fire or explosion.
Discussion: This is a safe and fun demonstration of Newton’s Third Law: Action and Reaction. NASA rockets, helicopters, even the lift of a bird’s wing involves this principle. The downward force (water+air) creates an equal upward force that rapidly accelerates the rocket. The force quickly diminishes but the energy causes the rocket to coast upward as it converts its speed to altitude. The velocity of the exhaust (water/air) is much higher than the velocity of the rocket itself. The reason is that the same force accelerating the air/water which is much lighter than the rocket. Astronauts do not experience the greatest “G” forces at lift off but as the spent fuel lightens the weight of the rocket the acceleration increases until the fuel is used up or the rocket engines are shut down. Large man carrying rockets have carried passengers into orbit, the International Space Station, and the Moon.
Learn more: This is a companion experiment to the Newton Carts. Nice demonstration of Newton’s.