Pressure

Let's talk about pressure. Well, everybody knows pressure is force divided by area, but we need to look a little further into it. The reason is this: let's say I have a surface like this, right? And let's say that this is the normal direction, right? And if I have a particular force, let's say this, right: F. Is now the pressure F divided by A? No, not quite. I have to look at the normal force component. The normal force component divided by the area, right? So, this particular case, for instance, if this is alpha, it's going to be F times, not sine, but cosine of alpha, divided by the area of the surface, will be my pressure. Okay? So be careful about this normal. And the units of pressure is Pascal in SI and psi in British gravitational units: Pascal and psi.