Pressure is a measure of how concentrated a force is.  There are many units for pressure but the ones that you will come across most often are N/m², N/cm² , or N/mm² . Other units of pressure that you need to know are the Pascal (Pa). 1Pa = 1 N/m².  All you need to know is the symbol not the conversion factor.  other units of pressure that exist but you will not be examined on are the atmosphere, (atm), millibar, (mB), mm of mercury, and torr.

A force spread over a small area creates high pressure.  the same force spread over a larger area creates low pressure. this is why tanks can cross muddy ground but a car gets stuck as the tank’s tracks spreads its weight over a larger area. the same principle applies when you are lying on a bed of nails.

Hydraulic systems use this principle to act as a force multiplier. this works as liquids are very hard to compress. A small force is applied to a piston with a small area.  This is connected to a larger piston that can lift a larger force.

e.g.

A 5N force is applied to a piston with a 1cm² area. This is connected by a hose to a piston with a 10cm² area.

pressure is calculated using the formula

pressure = force/area

               = 5N/1cm²

     = 5N/cm²

re arranging the formula to calculate the force applied by the large cylinder

force = pressure x area

• =5N/cm² x 10cm²
• = 50N

This is how car brakes work as well as all other hydraulic systems.

Extra videos

Here are 4 extra videos that hopefully explain and illustrate the nature of pressure through more examples.

How fluid power works

everyday examples of fluid power

hydraulic and pneumatics part 1

Hydraulics and pneumatics part 2