Balloon Rocket
The mass of a rocket can make the difference between a successful flight and a rocket that just sits on the launch pad. As a basic principle of rocket flight, a rocket will leave the ground when the engine produces a thrust that is greater than the total mass of the vehicle.
Large rockets, able to carry a spacecraft into space, have serious weight problems. To reach space and proper orbital velocities, a great deal of propellant is needed; therefore, the tanks, engines, and associated hardware become larger. Up to a point, bigger rockets fly farther than smaller rockets, but when they become too large their structures weigh them down too much.
What you need
- Large long balloons
- Fishing line
- Straws
- Small paper cups
- Paper clips
- Tape
- Clothes pins
- Scales
What to do
Step 1. Attach a fishing line to the ceiling or as high on the wall as possible. Try attaching a paper clip to a fishing line and hooking it on to the light or ceiling tile braces. Make one drop with the fishing line to the floor or table top per group. Note: The line may be marked off in metric units with a marker to aid students in determining the height traveled.
Step 2. Blow up the balloon and hold it shut with a clothes pin. You will remove the clip before launch.
Step 3. Use the paper cup as a payload bay to carry the weights. Attach the cup to the balloon using tape. Encourage students to think of creative locations to attach the cup to the balloon.
Step 4. Attach the straw to the side of your rocket using the tape. Be sure the straw runs lengthwise along the balloon. This will be your guide and attachment to your fishing line.
Step 5. Thread the fishing line through the straws. Launch the rocket by removing the clothes pin.
Balloon
Rocket.
Step 6. After trying the rocket see how much weight it can lift to the ceiling. Why not change the design in any way that might increase the rockets lifting ability. Try adding additional balloons, changing locations of the payload bay, replacing the initial balloon as it loses some of its elasticity enabling it to maintain the same thrust, etc.
What's Happening
When you blow up a balloon, you force air into a small space. Air particles don't like to be squished (engineers call it "compressed"). The particles want to move to a less crowded area. When you let go of the clothespeg, the air in the balloon rushes out to the lower pressure (less crowded) room. All that air rushing out the back of the balloon pushes it forward. Remember, for every action-air rushing out the balloon opening-there is an equal and opposite reaction-the balloon rocket shooting up the fishing line.
Tips
The fishing line should be taut for the rocket to travel successfully up the line, and the clipped balloon nozzle must be untwisted before release.