How can you increase the size of a blown balloon without pumping more air into it?

What you need:

A balloon, table lamp, measuring tape, piece of paper and a pen.

What you do:

1. Blow the balloon and measure the length of its widest part or circumference with the measuring tape. Write down the measurement.
2. Hold the balloon under the table lamp for 3 to 4 minutes, slowly rotating it all the while. Take care that the balloon does not touch the lamp.
3. Measure the circumference of the balloon once again while continuing to hold it under the lamp (you may need the help of an older person to do this).

What do you observe?

1. The balloon has become smaller.
2. The balloon has become bigger.
3. There is no change whatsoever in the balloon.

You will find that the balloon has become a little bigger.

Why does this happen?

The heat of the lamp warms the air inside the balloon. When the air becomes warm it expands, making the balloon bigger.

Picture Credit : Google