Other Relevant Demos :

• Bottle and Tube
• Gas filled bulb and U-tube manometer

Concepts demonstrated :

• Thermal expansion of solids and cavities.

Equipment needed :

• ball and ring
• plate with hole
• bunsen burner and matches
• liquid nitrogen
• ruler
• CCD camera

• Light a bunsen burner and have it ready to heat an object or the material surrounding a hole or cavity.
• Heat various substances and show that they expand.
• The experiment may also be performed by cooling various substances in liquid nitrogen (thermal contraction).
• Show the thermal expansion (contraction), if necessary using a ruler to show the extent of the expansion (contraction).

Physics involved :

Most materials when heated will expand (water being one exception when its temperature is close to zero degrees celcius). If various metals are heated in a bunsen flame then they will expand. Conversely if they are cooled they will contract. If a metal plate containing a hole is heated then the whole plate will expand including the hole.
Imagine a circle drawn on the plate with no hole.

How to use the Demonstration :

• Use as a POE.
• Ask the students what will happen to a solid when heated (it expands).
• Ask the students what will happen to a hole when the material surrounding the hole is heated (it also expands).
• Perform some of the experiments.
• Hold the ball and ring up to the class and show them that the ball does not pass through the ring.
• Ask the students how the ball could be made to fit through the ring.
• Perform the experiment by heating the ring and show that the ball does indeed pass through.

• Heating a metal lid on a glass bottle in order to remove the lid.
• "Shrink fitting". Get a color and a rod that are too tight for each other. Heat the color and cool the rod so that the color fits over the rod. When the both return to their normal temperatures you have a very strong grip with no weld.

• Construct a metal plate with different sized holes.

• Students usually believe that when the metal surrounding a hole is heated then the hole will get small when it actually should increase in size.
• This is a good demonstration because it highlights the misconceptions students develop. They like to think that the hole gets smaller.
• A variation on this experiment would be to have a metal ball that does pass through the ring, but when heated does not.
• Students find this demonstration very helpful.