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Balloon Rocket

The balloon rocket is a great science experiment for kids to grasp the concept of force and energy. By involving in this activity, they also garner a lot of fun as it enables them to build their own balloon-powered rockets, something that is no less than an exciting toy.

Balloon Rocket

Balloon Rocket

Balloon Rocket Experiment

Hypothesis

On releasing the air contained in a fully blown balloon, it moves forward along a straight string to which it is attached.

Materials

  • 1 balloon (long ones work best)
  • About 10-15 ft long kite string
  • 1 plastic straw
  • Tape

Steps

  1. Tie one end of the string to a door knob, chair or any other support.
  2. Pass the other end through the straw.
  3. Stretch the string tightly by pulling the free end and tie it to any other support.
  4. Move the straw to one end of the string. Blow the balloon up fully.
  5. Pinching its opening without tying it, tape it horizontally to the straw ensuring that the opening faces the support that is closest to the balloon.
  6. Let go of the pinched end and watch the balloon propel itself forward from one end of the string to another. Can you hear a noise? It is of the blown air escaping out.
Balloon Rocket Experiment

Balloon Rocket Experiment

How to Make a Balloon Rocket: Video

Explanation of the Balloon Rocket Lab

On releasing the nozzle, the air that is stored inside the balloon at a high pressure rushes out in the backward direction with a lot of force because of relatively lower pressure outside. This is the action. Now According to Newton’s 3rd law of motion, every action has an equal and opposite reaction. As a result, the thrust caused by the backward movement of the air causes the balloon to go in the forward direction. According to Newton’s 2nd law, the thrust produced is directly proportional to the acceleration produced in the rocket and they occur in the same direction.

The same principle is utilized in rockets. A part of it is filled with fuel. On burning, it gives rise to smoke and gasses that rush out of its rear in the downward direction, causing a thrust on the rocket to gain upward momentum.

According to Newton’s 1st law of motion, a body continues to be in a state of rest or of motion unless acted upon by some externally impressed force to act otherwise. Note that the only resistance to the motion of the balloon rocket is air resistance and the friction on the string that causes it to stop eventually. In the absence of both these factors, its velocity would never be zero. This helps us to conclude that a balloon rocket can operate in space that is a vacuum. This fact applies to real rockets too that are sent to a planet’s orbit in outer space.

Further Investigation

  • Measure the circumference of the widest part of a small inflated balloon with a tape. After performing the experiment, measure the distance traveled by setting a ruler along the straight string. Repeat with bigger balloons having greater circumferences at their centers. Tabulate the results and plot it on a graph taking the circumference (or radius) along the X-axis. How does it change?
  • Take different shapes of balloons and check how far they go. How does the rocket design affect the distance traveled?
  • Tape the balloon to the string in such a way that its nozzle is not parallel to the string but aligned at a certain angle. Execute the experiment. Does the rocket move as expected?
  • Use other types of material for your line like twine, fishing line or ribbon. How does it affect the distance up to which the balloon rocket travels?

Do let us know of your observations and let us figure out the reasons for it.

Applications of Balloon Rockets

You can make a racer balloon rocket car by applying the above principle of balloon rockets.

Turn it into a fun game by allowing children to race against each other with their homemade balloon rockets. Help them with tips and tricks to make it faster. Even preschoolers can enjoy its working as a toy without having to delve much into the details. It is also an ideal project for demonstration at science fairs.