Pressure in Liquids and Gases
How a squeeze on water or air spreads out in every direction
Big Idea: Unlike a solid, a liquid or a gas cannot keep its shape. Its tiny particles slide and fly around freely. Because of this, when you press on a trapped liquid or gas, the push does not stay in one spot — it spreads out and presses equally in all directions. This one simple fact explains water taps, dams, hydraulic car lifts, and even how your ears feel funny at the bottom of a swimming pool.
By the end you will be able to:
- explain why liquids and gases press in all directions, not just down,
- state Pascal's law and use it to explain the hydraulic press,
- calculate the pressure inside a liquid with p = ρgh,
- predict the liquid levels in communicating vessels,
- describe how a manometer measures pressure.