Define pressure as force per unit area; recall and use the equation p = F / A
1.8 Pressure
What is Pressure?
Pressure is the amount of force applied per unit area. Think of it like the way you feel when you press your hand against a table – the harder you press, the higher the pressure.
Mathematically:
$$p = \frac{F}{A}$$
where $F$ is the force in newtons (N) and $A$ is the area in square metres (m²).
The SI unit of pressure is the pascal (Pa), where 1 Pa = 1 N m⁻².
Real‑World Analogy
Imagine you’re pushing a pizza box. If you press with the same force but spread it over a larger area (like using a flat hand), the pressure felt by the box is lower than if you press with a small, sharp tip. This is why a needle can puncture a balloon but a broad hand cannot. 📏 Tip: The smaller the area, the higher the pressure for the same force.
Example Calculation
| Force (N) | Area (m²) | Pressure (Pa) |
|---|---|---|
| 100 | 0.01 | $10{,}000$ |
| 50 | 0.05 | $1{,}000$ |
Notice how halving the force but increasing the area reduces the pressure dramatically.
Exam Tips 🎓
- Always write the formula $p = \dfrac{F}{A}$ before starting a calculation.
- Check units: convert force to newtons and area to square metres before plugging into the formula.
- Remember that pressure is a scalar; it has magnitude but no direction.
- Use the symbol $p$ for pressure, $F$ for force, and $A$ for area.
- When dealing with liquids, pressure increases with depth: $p = \rho g h$ (where ρ is density, g is gravity, h is depth).
Revision
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