Vacuum Pump (Sara Wilson)


Sara Wilson

Columbus Middle School - 7th/8th grade teacher


Differences between sound/light waves

Air pressure

Boiling as a function of pressure


6.4.e Students know differences in pressure, heat, air movement and humidity result in changes of weather.

7.5.g Students know how to relate the structure of the eyes and the ears to their function.

Physics 4.a Students know waves carry energy from one place to another.

Materials needed

Bell Jar and Silicone gel/Rubber pad for airtight seal

Small buzzer

Shaving cream

Balloon filled with air

Flask with water


Sound wave investigation

  1. Put a small buzzer underneath the bell jar and turn on
  2. Place silicone around the base of the jar
  3. Turn on the vacuum pump and make observations of changes to the sound level
Air Pressure investigation
  1. Put a small amount of shaving cream or a balloon filled with air under the bell jar
  2. Place silicone around the base of the jar
  3. Turn on vacuum pump and make observations of changes to the shaving cream or balloon
Boiling as a function of pressure demonstration
  1. Place a flask partially filled with water under the bell jar
  2. Place silicone around the base of the jar
  3. Turn on vacuum pump and make observations of changes to the water in the flask


Sound wave investigation - Sound requires a medium (air) to travel through. When the vacuum removes all the air then the sound can no longer travel without the medium to travel through. Sound is a wave that travels by vibrating the air particles in the environment and if there is no air to vibrate no sound will occur. (Like in a vacuum)

Air Pressure Investigation - The air in an environment exerts a force (usually 1atm of pressure). If you remove the air then you remove that force and matter will expand without the force holding it in place.

Boiling as a function of Pressure Demonstration - The boiling of a liquid is a function of not only temperature but of pressure. By removing the air from a vacuum pump it causes the liquid to boil and change state to a gas.


  1. How are sound waves different than light waves? Explain.
     - Ans. - Sound waves need a medium (material like air, etc...) to travel through and light waves don't. That is why light reaches us from the sun but sound doesn't.
  2. Why do astronauts have to use a spacesuit to live in space? Why don't they just use a mask and oxygen tank like scuba divers? Explain using academic language.                     - Ans. - Air exerts pressure on your body. Without that pressure your body may have problems functioning beyond not being able to breathe.
  3. Why does water boil at a lower temperature at higher elevations? Explain with evidence.   - Ans. - When there is less air pressure, like at higher elevations, then the pressure contributes to the boiling of water and allows it to boil at lower temperatures.

Everyday examples of the principles illustrated

  • High altitude adjustments to cooking recipes
  • Insulated glass limiting sound transmission
  • Driving to high elevations, sometimes chips bags explode from air pressure differential
  • Ear-popping at high elevations as well.


Image of large vacuum pump in my classroom. Missing bell jar.


Include movies that you have taken.  Your movies should be placed in your youtube account. 


Physics classroom - sound

PhET sim - sound waves

USGS on sound waves

NASA - Atmospheric pressure

USA Today - "Understanding Air Pressure"

U of Illinois - Atmospheric Pressure

Engineering Toolbox - Boiling point and atmospheric pressure

WISC - How pressure changes boiling temperature