What exactly is pressure?


I can’t seem to wrap my head around the term pressure.

Vehicle tyres use air pressure, toilets faucets etc use pressure (presumably water pressure),
pressing onto something applies pressure, our blood has pressure, temperature is also affected by “pressure”.
I know there are various types of pressure, and I can’t think of any more examples at the moment, but my point is “pressure” sounds like a very arbitrary or vague umbrella term to me.

Help me make sense of it?

In: 3

Fluid (liquid and gas) particles are always in constant and random motion. When they bounce off of each other and hit the walls of their container, they exert a certain amount of force on it. The average amount of force exerted by these particles per unit area is defined as pressure. When something’s temperature increases, it gains kinetic energy, also known as ‘movement’ energy. When something’s kinetic energy increases, it moves faster. As you can guess, when particles begin to move faster, they bounce off of each other more often and collide with their surroundings at faster speeds, exerting a higher force. Thus, pressure increases with temperature.

Pressure is the total force in an area divided by the area itself. So you can think of it as the force intensity over a certain area.

If the pressure is 10N/m^2, then that pressure existing on an object with the area of 1m^2 results in that object experiencing 10N of force. Pressure is a useful measure because it normalizes the calculation by area and thus the outcome can be scaled easily.

The formula for pressure is force per unit of area. There is pressure whenever there is a force applied to an area. What force and what area is arbitrary, so the definition is kinda vague.

Usually the force is a mechanical one. Air pressure in a tyre is related to the force air has inside the tyre. Blood pressure is related to the force blood is pumped in your veins and arteries. And so on.

You actually got it in your response: pressure is basically how hard something is pressing against something else. It’s the “press” in pressure.

Air pressure in your tires is how hard the air is pushing against your tire walls, water pressure in a faucet is how hard the water is pressing against the air as it exits, blood pressure measures how hard your blood is pushing against your blood vessel walls, etc.

Intuitively, pressure is a measure of how much the particles in a liquid or gas (or even a solid sometimes) are pushing on their neighbors because of crowdedness. Particles can be crowded because there’s a lot of them packed into a tight space, or because they’re hot so they want to take up more space, or both.

Numerically, pressure is measured by asking how many units of force it pushes with, per unit of surface area. One common pressure unit is PSI, or “pounds per square inch.” If you inflate your bike tire to 50 psi, that means that each square-inch of rubber in the tire, is receiving 50 pounds of outward force from the air inside it.