Measuring the vacuum
Inflate the balloon from the outside!
Safety
- Carefully review the general safety advice on the back of the box cover before starting the experiment.
- Disassemble the setup after the experiment.
Disposal
- 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.
