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.
In this “trash-to-treasure” activity, polystyrene clamshell containers (#6 plastic) are used to make hard plastic art pieces. When polystyrene clamshell containers are produced, the material is heated and stretched into a mold, thus locking the material in an extended state. When this material is heated again, it returns to its unstretched size and shape. This property can be utilized to create a range of crafts, including buttons, key chains, luggage tags and jewelry. If students mass their plastic before and after, this could also be tied to the Law of Conservation of Mass.