Pressure & Air Pressure
Pressure = Force / Area
Force = Pressure * Area
Area = Force / Pressure
Air pressure is caused by particles of air colliding with a surface.
A ballon expands when placed in a vacuum jar becuase there is more air inside the baloon forcing the material outwards.
The Magdeburg Hemispheres are difficult to pull apart beucase the pressure of the air outside of the hemispheres is much greater than that on the inside.
A brake uses hydraulics to slow a car down. The design of the system makes it a force magnifier. If the slave pistons (the ones near the brakes) have twice the area of the master piston (the one nearest the drivers foot) they will exert twice the force that the driver applies with his foot.