Fluid Forces
Dive deep and your ears hurt; climb a mountain and your crisp packet puffs up. Learn how pressure works in liquids and gases — p = F/A, why it grows with depth, and why the air thins out as you rise.
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Fluid Forces 🌊
A **fluid** is anything that flows — a liquid or a gas. Fluids press on everything they touch, and that push is **pressure**. From the crush of the deep sea to the thin air on a mountain top, pressure shapes the world around you.
Pressure 📏
**Pressure** is the force pressing on each unit of area: **p = F / A** with p in **pascals (Pa)**, F the force in newtons and A the area in m². In a fluid **at rest**, pressure acts **equally in all directions** — not just downward.
Find the pressure
An interactive activity.
Find the force
An interactive activity.
Deeper means more 🤿
**(Higher tier)** The deeper you go in a fluid, the **more fluid there is above you** pushing down — so **pressure increases with depth**. The equation is: **p = h ρ g** pressure = depth (h) × density (ρ) × gravitational field strength (g). It is why dam walls are built thicker at the bottom.
Pressure at depth
An interactive activity.
Diving deeper
An interactive activity.
Atmospheric pressure 🎈
The air around us has weight too. **Atmospheric pressure** is caused by **air molecules colliding with a surface**. High up a mountain, or in a plane, the air is **less dense** — there are fewer molecules above you and fewer collisions — so **atmospheric pressure decreases as altitude increases**.
Pressure facts
Select ALL THREE statements about pressure in fluids that are TRUE.
- Pressure in a fluid at rest acts equally in all directions
- Pressure in a fluid increases with depth
- Atmospheric pressure decreases as altitude increases
- Pressure in a fluid only acts downward
- Pressure decreases as you go deeper into a fluid
- Atmospheric pressure increases as you climb higher
Match each term to its meaning
- Pressure
- Pascal
- Atmospheric pressure
- Density
- The force acting on each unit of area
- The unit of pressure, equal to one newton per square metre
- The pressure from air molecules colliding with a surface
- The mass of a material per unit volume
Fluids summary
Pressure is force per unit area: p = F / _____, measured in pascals. In a fluid at rest, pressure acts equally in all _____, and it increases with _____. Atmospheric pressure comes from air molecules colliding with a surface, and it _____ as altitude increases.