# PRESSURE

#### branchMECHANICS (MOTION)

=Pressure= Pressure is defined as the Force per unit Area. This relationship can be expressed using the following formula: ==='''P''' (Pressure) = '''F''' (force) ÷ '''A''' (Area)=== The unit for pressure is '''Newtons per metre squared (Nm^-2^)''' or '''Pascals (Pa)''' ===Applying the same force to a smaller area results in a greater pressure.=== [image:http://i.imgur.com/R92d7aq.png?1] This is why it would hurt so much more if someone stood on your toes wearing high heels. It's also why high heels will sink into the ground if it's too soft. The weight force doesn't change, but with high heels the force force is applied over a smaller area and thus a greater pressure is generated. ===Applying the same force over a larger area results in a lesser pressure.=== [image:http://i.imgur.com/1dx632N.png?1] This is why a person can lie on a 'bed of nails' without injury. The force is spread across a large enough area that the pressure is reduced sufficiently that it can't pierce the skin. ===Pressure is a ratio of Force to Area=== [image:http://i.imgur.com/NtlM8mQ.png?1] People leave footprints in wet sand because of the pressure applied by their feet. Children and Adults may leave similar depth impressions (footprints) because they apply a similar pressure. Although a child weighs significantly less they also have much small feet. This means that while their weight force is smaller, the area over which the force is applied is also smaller. This means that the resulting pressure is still comparable to that of an adult. ==Calculating Pressure== [image:http://i.imgur.com/VUkW77o.png?3] Pressure can be calculated by dividing the '''Force''' by the '''Area''' over which it is applied. The formulae can also be rearranged to calculate the '''Force''' or the '''Area''' over which it is applied. ==Applications== [image:http://i.imgur.com/SmXpnhX.png?2] Hydraulic brakes use pressure in order increase the force applied to the break pads. When a driver steps on the brake pedal a small force is applied to a piston with a small area. This generates pressure inside a hose filled with break fluid. The pressure generated causes a larger piston to apply a larger force to the break pads. The pressure remains constant throughout the system. This allows a small force to be applied over a smaller area, resulting in a larger force applied over a larger area.
Credit: Ben Himme, Tristan O'Hanlon