Pressure is defined as force per unit of square area. Pressure is measured in pascals (Pa) which is equal to one Newton per square meter.
Pressure, pressure is the force per unit of surface area, what does that mean? Well if I sit down on a chair, I'm applying the force of my body over the surface area of that chair and that probably doesn't hurt. If I sit down on a nail I'm applying the same force but on a very very small surface area and that's going to hurt a lot right so that's just the same amount of force supplied over a very very much smaller surface area and that's how we can just think about pressure okay?
Now the unit of pressure, we measure in Pascal's so Pascal is one Newton per square meter okay, a kilopascal is 1000 Newton per square meter okay? So those are terms we're going to use.
A common pressure that we talk about is air pressure. When we talk about weather, barometric pressure and the unit for that is 101.3 kilopascals and you say wait a minute if I'm standing at sea level, that's a lot of force 101.3 kilopascals? Well remember you're used to the air pressure but remember the atmosphere goes up many many many kilometers and all that air is forcing down and it's considerable pressure okay? An example of that from Chemistry we have the ideal gas law which says that pressure is related to many things and this is a good way to discuss pressure so we can say that pressure is related to the amount of a substance so if I add more of a gas to a given area it's going to increase the pressure okay, it's also due to the temperature if I heat up a gas in a given area it's going to its molecules are going to move faster and it's going to increase the pressure with the force applied to that surface area okay, also the volume if I take a volume and I compress it and reduce the volume that's going to increase the pressure of that gas so the ideal gas kind of exemplifies how pressure factors that can change the pressure just in the volume, changing the temperature, these are all things that will change the pressure of a gas and that's a just a brief introduction to what pressure is.