Materials:1 jingle bell, a glass bottle with lid, hot plate, water, some glue.
Get a large glass bottle with a metal lid. Find a jingle bell that will fit through the mouth of the bottle. Use a little glue (be careful with your glue. The steam will make some glue fail) to glue a jingle bell by the string from the inside of the lid. When the lid is on the bottle the jingle bell will dangle down into the bottle.
Shake the your bottle to hear the bell jingle. Remove the lid and pour some water (perhaps 20 mL or so) into the bottle and heat it to boiling with your hot plate. Let it boil for for a while - at least one minute.
Carefully and immediately put the lid onto the bottle with the bell into the bottle. (Remember the bottle will be HOT and can easily burn you! Use a towel or other protection from the steam and hot glass.) Remove the bottle from the heat and allow to cool. After letting the bottle cool off for a minute shake it again to hear you bell jingle. Can you hear the bell now?
OK, you can still hear the bell but not as well. Why?
During the boiling process water was being converted from a liquid to a gas and pushing air out of the bottle. When the lid goes onto the bottle the and the heat is removed the evaporated water cools and becomes a liquid again and is no longer acting like air. So a partial vacuum (much lower air pressure) is formed inside. Since air carries sound vibration and their is less air inside the bottle the sound does not carry very well.
In the first case sound energy was carried through air by making the air in the bottle vibrate and was transmitted to the glass, to the air on the outside of the flask, and then to our ears. But in the case where the water was boiled, the air was forced out of the bottle and replaced by water vapor. Upon the cooling of the water vapor the water molecules suddenly condensed into liquid water leaving most of the volume void of molecules. Shaking the bell now produced only a faint sound. The event occurred, but there was very little air through which it could be transmitted to reach our ears. If a perfect vacuum could be produced, no sound would be heard.
Return to the Science Alliance Home
Return to the Fairmount Center forScience & Mathematics Education Home