What is Pressure?
Pressure is defined as the force applied perpendicular to the surface of an object per unit of area over which that force is distributed. In simpler terms, it's a measure of how concentrated a force is.
For example, a sharp knife cuts better than a dull one because the same amount of force is concentrated onto a much smaller area, creating a much higher pressure. Similarly, a person wearing high heels exerts more pressure on the ground than a person wearing snowshoes, even if they weigh the same.
The Pressure Formula
The formula for pressure is:
- $P$: The Pressure, measured in Pascals (Pa). One Pascal is equal to one Newton per square meter (N/m²).
- $F$: The perpendicular Force applied, measured in Newtons (N).
- $A$: The Area over which the force is applied, measured in square meters (m²).
Other common units for pressure include pounds per square inch (psi), atmospheres (atm), and bars. The standard atmospheric pressure at sea level is approximately $101,325 \text{ Pa}$.
Pressure vs. Force
It's important to distinguish between pressure and force.
- Force ($F$): This is the total push or pull on an object. It's what causes an object to accelerate ($F=ma$). It is measured in Newtons (N).
- Pressure ($P$): This describes the *distribution* of that force over a surface. The same force can create very different pressures depending on the area.
Think about pushing a thumbtack into a wall. Your thumb applies a force to the large head of the tack. The tack transmits that same force to the wall, but through its tiny, sharp point. The area is so small that the pressure becomes high enough to pierce the wall, even though the force from your thumb was relatively small.