Yet More Pressure

Not content with the pressure that the world loads upon us, we add more pressure just by our very existence. Everything we come into contact with feels the pressure from us, and because of Newton’s Third Law which states that “for every action there is an equal but opposite reaction” we feel it too. This can sometimes be useful, sometimes painful and at other times just inconvenient.

Pressure is different to force when it comes to the interactions between us and other objects, because a force, for example one of 5N, is always the same. Pressure depends on both the force and the area over which that force operates. Hence we have to use the equation

to find out the pressure. You can see that if the area is very small, the pressure is very high. An example of this would be the point of a nail, deliberately made to have a tiny cross-sectional area at the tip so that the high pressures created by hitting the other end drive it into the material. Conversely, the other end of the nail has a comparatively large area to spread the force of the hammer, so that it doesn’t damage the hammer.

So next time you’re having trouble carrying that shopping bag that’s cutting into your hand or wanting to make a hole in something (appropriate, of course, not like your little brother’s head) then think about pressure. Do we want to reduce the pressure? Then increase the area. Do we need more pressure? Then decrease the area.