As the liquid nitrogen is poured over the eraser bits, they start to pop and jump!
Teachable Topics:
- Tensile Stress and Young's Modulus
- Temperature
- Material Science
Theory:
White erasers are made out of specialized rubber. Rubber has a very poor heat conductivity. For example, if you heated an eraser at one end, it would take some time for the other end to start to get warm. In this demonstration, a regular white eraser is cut up into chunks and covered in liquid nitrogen. Liquid nitrogen is approximately -196 〬C when it boils, and is extremely cold compared to the erasers. Just as rubber takes a long time to get hot, it also takes a long time to get cold. This means that the outer surface of the eraser chunks will get much colder than the inside of the eraser chunks. This creates a lot of stress in the rubber because the colder parts will contract while the warmer parts will not. When this stress gets too much, the eraser chunk will break or explode in an attempt to relieve the stress.
Apparatus:
- Liquid nitrogen
- Small pie plate or another small container
- White eraser
- Scissors/exacto knife
- Safety goggles & cryo gloves
Procedure:
- Cut up a white eraser into cubes (around 5mm on a side) with an exacto knife or scissors.
- Place the eraser chunks into a small pie plate or another small container.
- Carefully pour liquid nitrogen into the container with the eraser chunks.
- Wait for a few seconds and soon the erasers will start to explode.
- The size of the explosion is very dependent on the size of the rubber cubes, experiment to get the most bang for your buck.
