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Balloon Boarding

When a person puts his whole weight on one balloon, all of the pressure from that person is concentrated on one small area of the balloon, which results in the balloon bursting. When the person's weight is distributed over several balloons, the balloons do not burst because the pressure is spread over a large area. As a result, each balloon only supports a small fraction of the weight.

This trick only works if the balloons are not fully inflated. If this demonstration is done with fully inflated balloons, the rubber is already stretched out and is less elastic. Balloons that are only partially blown up still have the ability to stretch.

This is a recommended post-visit activity for a field trip to Science World.

This demonstration is similar to asking a volunteer to lie on a Bed of Nails, a common exhibit found in science centres: Check out the Science World Edition HERE.

If the volunteer were to sit on one nail, it would be extremely painful. But if the weight is distributed over hundreds of nails, there is very little pressure on each individual nail, rendering the experience quite comfortable. The difficulty is when the person is in the process of lying down or getting up, since her weight is distributed on fewer nails, resulting in more pressure being exerted on each nail.  

Objectives

  • Describe the concept of weight and force distribution.

Materials

  • Per Class or Group:
    a wooden board or door, or upside down table
    a large towel
    10–14 inflated balloons (about 75% inflated, not fully blown up)

Key Questions

  • How many people can stand on the board without the balloons bursting?
  • Why did we use partially inflated balloons?
  • What is happening to the balloons under the board?
  • Why did the teacher say not to jump onto the board?
  • If one student stands on one balloon, it will burst. How does putting a board over several balloons increase the balloons’ ability to carry weight?

What To Do

Safety
The following safety procedures are important to avoid panic and/or balloons accidentally popping.

  • The balloon board requires TWO people to hold on to the sides at all times to provide stability.
  • I​f using volunteers to hold board, be sure to choose mature volunteers who are able to stay focused.
  • ​Keep order throughout demonstration. Bring people onto the board one at a time and stop if kids are rushing towards the board. Likewise, at the end of the demonstration, have people come off board one at a time.

Preparation

  1. Blow up the balloons, but not fully (75%). It can help to blow the balloons up completely and then let air out until they’re at 75% full.

Instructions

  1. Spread the towel out on the floor.
  2. Ask for two volunteers. Place all of the balloons on the towel. Help the volunteers place the board on top of the balloons.
  3. Position one volunteer at either side to stabilize the board.
  4. Invite another student volunteer to step onto the board. Remind him not to jump or bounce.
  5. Continue adding students until the balloons start bursting.

Extensions

  • Try reducing the number and/or placement of the balloons.
  • Try fully inflated balloons.
  • What would happen if the board wasn’t there? Could a student lie over the balloons without bursting them?
  • The ‘bed of nails’ circus trick also relies on the principle of spreading the weight of the person lying on the nails. This can be shown with an experiment using a balloon and a small scale model of a bed of nails. Check out Science World's bed of nails video.

Other Resources

Science World Bonus | Video | The Science of Lying Down on a Bed of Nails