DESCRIPTION:
In this demo a ping pong ball with a hole along the seam is submerged in liquid nitrogen (-196⁰C) to fill it. When removed, the nitrogen in the ball boils and is forced out of the hole in a stream. The stream, which comes out at an angle, causes the ball to spin away from the stream. The “stream” that we see is condensed water vapor, not nitrogen gas.
TOPICS COVERED:
– cryogenics
– vaporization
– condensation
– Newton’s 3rd Law of Motion
MATERIALS NEEDED:
– tongs
– liquid nitrogen
– bucket
-ping pong balls with holes
PROCEDURE:
1. using tongs, submerge the balls in liquid nitrogen
2. Pull the balls out and let them spin around the table or floor
ADDITIONAL COMMENTS:
Use a thin stick pin to poke a hole in seam of the ball at an angle tangent to the seam. Stripes can be drawn on the ball with a permanent marker so it’s easier to see that the ball is spinning.
SAFETY:
Liquid nitrogen is a cryogenic hazard and can cause severe skin burns. Safety goggles should be worn at all times.
STORY:
Many student have heard “for every action there is an equal but opposite reaction” (Newton’s 3rd Law of Motion) but they don’t really know what it means. This is a great demo for that.