Measuring the vacuum

Inflate the balloon from the outside!

15 minutes
Measuring the vacuum


  • Carefully review the general safety advice on the back of the box cover before starting the experiment.
  • Disassemble the setup after the experiment.


  • Dispose of solid waste together with household garbage.

Scientific description

Vacuums can be measured using a special device—a vacuum gauge—which shows how much greater Earth’s atmospheric pressure  is than the pressure  in the hood  where some air  has been removed. The vacuum gauge is connected to the vacuum unit through a tube without valves. The air pressure  is the same in both of them. As you remove air  from the vacuum unit, the air pressure  drops in the entire installation.

The vacuum gauge has a moving piston  connected to a spring . External air  presses  on the piston , while internal air  pushes  it in the opposite direction. When you remove air  from the unit, the pressure  inside it becomes lower than the pressure  outside it, and the external air  compresses the piston spring . The greater the pressure difference , the more the spring is compressed . Thus, your vacuum gauge shows how much air you have pumped out.

The inflated balloon  expands because the air pressure  inside it is greater than the pressure  of the Earth’s atmosphere. The pressure  builds as you inflate the balloon . In the hood , the air  pressure  is even lower than atmospheric pressure , which causes the balloon  to expand even more.