Vibrating pennies – conduction experiment
Take a bottle with a narrow opening. The opening should be just about the size of a penny.
- Dip a penny in a bowl of ice water. Hold the neck of the bottle in the ice water for a few seconds too.
- Place the penny over the mouth of the jar.
- Place some oil around the bottles opening or on the penny in order to provide a completely air tight seal.
- Now hold bottle in your hands and carefully observe the penny. It should begin bouncing around. Rubbing the bottle will increase the heat even more.
Remember – heat causes things to expand (or get larger). Cold causes things to contract (or get smaller). The heat from your hands is transferred through conduction to the air in the bottle warming the air. This causes the air molecules to move faster which makes the penny jump. As this happens the pressure in the bottle is increased forcing the penny upward. A little bit of the air escapes and the penny falls back down. Then the heat generates more pressure and the process continues causing the penny to repeatedly lift and fall on the mouth of the bottle.
Conduction is the transmission of something through a medium or passage – in this case, the transmission of heat from your hands to the air in the bottle. The rate of heat flow between the two regions is proportional to the temperature difference between them.