Vibrating Coin

Purpose

To demonstrate the expansion of air when heated.

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Additional information

The temperature of a gas is directly proportional to the speed with which its molecules move. Increasing the temperature of a gas results in an increase of the average speed (and therefore the kinetic energy) of its molecules. This in turn causes the molecules to ‘spread out’ by virtue of a phenomenon known as thermal expansion.

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Required materials

• Coin
• Bottle
• Refrigerator
• Water

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Estimated Experiment Time

Approximately 15 to 20 minutes

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Step-By-Step Procedure

• 1. Place an empty bottle in a refrigerator to cool
• 2. Place the cooled bottle outside
• 3. Dip your finger in water and place a few drops around mouth of the bottle and the edge of the coin
• 4. Place a coin on the mouth of the bottle
• 5. Place both your hands around the bottle; hold firmly
• 6. Remove your hands after a while

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Note

• Use a bottle with a mouth narrow enough to be closed completely with a coin.
• Applying water on the rim of the bottle mouth and the coin’s edge will help seal the bottle.

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Observation

In approximately fifteen seconds from covering the bottle with your hands, the coin will start to vibrate up and down. When you do remove your hands after a short while, the coin continues to vibrate.

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Result

As soon as the bottle is taken out of the refrigerator the temperature of the gas inside the bottle begins to rise; encasing the bottle with your hands increases the temperature further. When the bottle is heated, the air molecules inside it start moving faster and these molecules collide with the coin with more energy. This results in increased pressure which in turn is caused by the expanding air that escapes though the rim of the coin and makes it vibrate.