Caused by molecular collisions which transfer momentum Generally a function of pressure and temperature - Liquids are insensitive to moderate changes in pressure - “incompressible” - Gases are sensitive to changes in both pressure and temperature - [[Ideal Gas Law]] Normal force per unit area $ P=\lim_{A\rightarrow0}\frac{F_n}{A} $ $ \text{Pressure}=\frac{\text{Force}}{\text{Area}}\quad [\text{Pa}]=\bigg[\frac{\text{N}}{\text{m}^2}\bigg]=\bigg[\frac{\text{kg}}{\text{ms}}\bigg] $ - $1\text{ atm}=101,325\text{ Pa}$ - $1\text{ bar}=100,000\text{ Pa}$ Absolute pressure $ P_{absolute}=\rho gh+P_{atm} $ Gauge pressure $ P_{absolute}=P_{gauge}+P_{atm} $ $ P_{gauge}=\rho gh $ # Pascal's Principle Blaise Pascal (1623-1662, France) Pressure applied on a fluid is distributed uniformly throughout its volume Results in: $ P_{input}=P_{output} $ - enables hydraulics