Force is a push or pull, while pressure tells us how concentrated that force is over an area. This easy guide covers balanced and unbalanced forces, the pressure formula, SI units and everyday examples.
What Is Force?
Force can move a stationary object, change the speed or direction of a moving object, or change its shape. Its SI unit is newton (N). Pushing a door, kicking a ball and stretching a rubber band are examples of force.
Balanced and Unbalanced Forces
Equal opposite forces have a net force of zero and are called balanced forces. A book resting on a table is supported by balanced forces. When forces are unequal, the net force is not zero and the motion can change.
Pressure: Formula and SI Unit
Pressure is force per unit area:
P = F/AThe SI unit of pressure is pascal (Pa), equal to one newton per square metre. For the same force, a smaller area produces greater pressure.
Everyday Examples of Pressure
Wide school-bag straps
Wide straps spread the same force over a larger area, so the pressure on your shoulders is lower.
A pointed nail
A nail has a tiny contact area at its point. The same force therefore creates greater pressure and helps it enter wood.
Snow shoes
The wide base spreads body weight over a larger area, so a person sinks less into snow.
Solved Numerical
If F = 100 N and A = 2 m², then:
P = F/A
P = 100/2
P = 50 PaThe pressure is 50 Pa. Use newtons for force and square metres for area to get pascals.
Pressure in Liquids and Air
Liquids and gases also exert pressure. Liquid pressure increases with depth, which is why dam walls are made thicker near the bottom. Air around us also exerts atmospheric pressure.
Common Mistakes to Avoid
- Confusing pressure with force.
- Forgetting to convert area into square metres.
- Writing that pressure decreases when area decreases; use P = F/A to check.
- Thinking balanced forces mean that no forces are present; their net force is simply zero.
Practice Question
A force of 60 N acts on an area of 3 m². Calculate the pressure. What happens if the same force acts on an area of 1 m²?
Key Takeaways
- Force is a push or pull.
- Balanced forces have zero net force.
- Pressure is force per unit area.
- Remember the formula P = F/A.
FAQs
What is the SI unit of force?
The SI unit of force is newton (N).
What is the formula for pressure?
Pressure equals force divided by area: P = F/A.
Why does a sharp knife cut easily?
Its sharp edge has a smaller area, so the same force produces greater pressure.
Need Help With Force and Pressure?
Send your attempt to DoubtPay AI for a hint, a simpler explanation, or a step-by-step check. Compare the result with your textbook or teacher.