Moving Things, People & Ideas (VI–VIII) • Topic 2 of 3

Force & Pressure

CTET recap: a force is a push or a pull on an object. A force can (1) move a stationary object, (2) stop a moving object, (3) change the speed of a moving object, (4) change the direction of motion, and (5) change the shape or size of an object — children should be able to give a classroom example of each. Forces acting along the same line add up if they point the same way and subtract (net = difference, in the direction of the larger) if they point oppositely. Forces are of two broad kinds: contact forces (muscular force, friction) and non-contact forces (gravitational, magnetic, electrostatic). Pressure is the force acting on a unit area: Pressure = Force ÷ Area, SI unit pascal (Pa = N/m²). The key idea children must build: for the same force, a smaller area gives larger pressure — which is why a sharp knife cuts better, a nail has a pointed tip, and a school bag with a thin strap hurts the shoulder while a broad strap does not. Liquids and gases exert pressure on the walls of their container and in all directions. Pedagogy & misconceptions: the deepest misconception is that 'force and pressure are the same thing' — the broad-strap-vs-thin-strap demonstration separates them. Another is that 'only living things or machines exert force' — a magnet and gravity are silent counter-examples. How it's tested: name the effect of a force in a scenario, compute pressure (or compare pressure for two areas), or pick the everyday application of the small-area = high-pressure rule.

✅ Solved examples

1. A force of 200 N acts on an area of 4 m². What pressure does it exert?
Pressure = Force ÷ Area = 200 N ÷ 4 m² = 50 Pa (N/m²). Divide force by area.
2. Why is the cutting edge of a knife made very thin?
A thin edge has a very small area, so for the same applied force the pressure (Force ÷ Area) is very large, letting it cut easily. Smaller area → larger pressure.
3. A football is squeezed and changes shape. Which effect of force is shown?
A force can change the shape (and size) of an object. (No motion change here — only deformation.)
4. A child insists 'force and pressure mean the same thing'. The best classroom demonstration is:
Have the child press a pencil first with the blunt end, then the sharp tip, on their palm using the same force. The same force, smaller area, more pressure (and pain) — separating the two ideas through experience.

✏️ Practice — try these, take hints as needed

1. A force of 100 N is applied on an area of 2 m². Find the pressure.
Pressure = Force ÷ Area.
Unit is Pa (N/m²).
50 Pa
2. A goalkeeper stops a moving ball with his hands. Which effect of force is this?
The ball was moving, then stopped.
One of the five effects.
A force can stop a moving object
3. Why do the foundations of a building have a large base area?
Same weight, bigger area.
Think Pressure = Force ÷ Area.
To reduce pressure on the ground (large area → low pressure)
4. The magnetic force and the gravitational force are examples of:
No touching is needed.
Opposite of contact forces.
Non-contact forces

📝 Topic test — 8 questions

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