NCERT Solutions: Force and Pressure (Class 8 Science)

Chapter overview

This chapter introduces force as a push or pull, the different types of force (muscular, frictional, gravitational, magnetic, and electrostatic), and how pressure relates force to the area over which it acts.

Key concepts

• Force can change the speed, direction, or shape of an object.
• Contact forces: muscular force and frictional force require the objects to touch.
• Non-contact forces: gravitational force, magnetic force, and electrostatic force act at a distance.
• Pressure formula: Pressure = Force / Area, measured in pascals (Pa) when force is in newtons and area is in square metres.
• Pressure is inversely proportional to area — the same force spread over a smaller area creates more pressure (why a sharp knife cuts more easily than a blunt one).

Worked practice problem 1 — Pressure calculation

Question: A box exerts a force of 200 N on the ground through its base, which has an area of 0.5 m². Find the pressure exerted by the box.

Solution:

Pressure = Force / Area = 200 N / 0.5 m² = 400 Pa

Answer: The box exerts a pressure of 400 Pa on the ground.

Worked practice problem 2 — Comparing pressure

Question: Two identical bricks are placed on soft ground, one flat side down (area 0.06 m²) and one on its edge (area 0.02 m²). If each brick weighs 24 N, which orientation sinks more into the ground, and by how much greater is the pressure?

Solution:

Flat side down: P₁ = 24 / 0.06 = 400 Pa

On edge: P₂ = 24 / 0.02 = 1200 Pa

P₂ / P₁ = 1200 / 400 = 3

Answer: The brick standing on its edge exerts three times the pressure of the same brick lying flat, so it sinks more into soft ground - even though the force (weight) is identical in both cases.

Types of force — quick reference

Force	Contact or non-contact?	Example
Muscular force	Contact	Pushing a door
Frictional force	Contact	A ball slowing down as it rolls
Gravitational force	Non-contact	An apple falling from a tree
Magnetic force	Non-contact	A magnet attracting iron filings
Electrostatic force	Non-contact	A charged balloon sticking to a wall

Common mistakes to avoid

• Confusing force and pressure - the same force can produce very different pressures depending on area.
• Forgetting to convert area units consistently (cm² vs m²) before calculating pressure.
• Assuming all non-contact forces are the same - gravitational, magnetic, and electrostatic forces behave differently and act on different types of objects/charges.

Looking for the official textbook PDF for this chapter? Visit our Class 8 NCERT Books page for the direct download link.