Want to stay on top of all the space news? Follow @universetoday on TwitterMaking a balloon rocket is one of the simplest ways to demonstrate Newton’s Third Law of Motion and some of the simple principles of physics. All you need is some string, a drinking straw, tape, and a balloon of course. You can visit nasa.gov and look for this .pdf Rockets: a Teacher’s Guide with Activities in Science, Mathematics, and Technology for additional information and experiments.
Let’s go over the principles of Newton’s third law: ‘To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. — Whatever draws or presses another is as much drawn or pressed by that other. If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tied to a rope, the horse (if I may so say) will be equally drawn back towards the stone: for the distended rope, by the same endeavor to relax or unbend itself, will draw the horse as much towards the stone, as it does the stone towards the horse, and will obstruct the progress of the one as much as it advances that of the other. If a body impinges upon another, and by its force changes the motion of the other, that body also (because of the equality of the mutual pressure) will undergo an equal change, in its own motion, toward the contrary part. The changes made by these actions are equal, not in the velocities but in the motions of the bodies; that is to say, if the bodies are not hindered by any other impediments. For, as the motions are equally changed, the changes of the velocities made toward contrary parts are reciprocally proportional to the bodies.’ That is a fairly direct translation from Newton’s text.
In the case of the balloon rocket, the air escaping from the end of the balloon causes the initial ‘action’ the ‘reaction’ is the movement of the balloon along the string in the opposite direction of the action. As the air rushes out of the balloon, it creates a forward motion called thrust. Thrust is a pushing force created by energy. Here the thrust comes from the energy of the balloon forcing the air out. Different sizes and shapes of balloon will create more or less thrust. In a real rocket, thrust is created by the force of burning rocket fuel as it blasts from the rockets engine – as the engines blast down, the rocket goes up.
- Tie one end of the string to a chair, door knob, or other support.
- Put the other end of the string through the straw.
- Pull the string tight and tie it to another support in the room.
- Blow up the balloon (but don’t tie it.) Pinch the end of the balloon and tape the balloon to the straw as shown above. You’re ready for launch.
- Let go and watch the rocket fly.
Making and flying a balloon rocket is a great tool to teach younger students the basics of thrust and Newton’s third law. Be sure to check out the NASA page mentioned above for more activities.
We’ve recorded an episode of Astronomy Cast all about Rockets. Listen here, Episode 100: Rockets.
Source: Science Bob