Revision Notes: Class 8 Science Chapter 5 Exploring Forces

Class 8 Science Chapter 5: Exploring Forces — Quick Revision Notes

• Force: a push or pull arising from an interaction between two objects; SI unit is the newton (N).
• Effects of force: can start motion, stop motion, change speed, change direction, or change shape — often a combination.
• Contact forces (require touching): muscular force (from muscle contraction) and friction (opposes relative motion between surfaces; greater on rough surfaces).
• Non-contact forces (act without touching): magnetic force (attract/repel between magnets), electrostatic force (from charge, like charges repel/unlike attract), and gravitational force (Earth’s pull, always attractive).
• Weight vs mass: mass is the fixed amount of matter (g/kg), constant everywhere; weight is the gravitational force pulling an object down (N), which varies by location — e.g. Moon’s gravity is about 1/6th of Earth’s.
• Spring balance: measures weight — the stretch of a calibrated spring is proportional to the weight hung on it.
• Buoyant force (upthrust): the upward force a liquid exerts on an object placed in it; per Archimedes’ Principle, it equals the weight of liquid displaced.
• Floating vs sinking: an object floats if buoyant force ≥ its weight, and sinks if its weight exceeds the buoyant force.

Frequently Asked Questions

What is a force, and what effects can it produce on an object?
A force is a push or pull acting on an object, and it can change the object speed, its direction of motion, or its shape, depending on the magnitude and direction in which the force is applied.

Last Updated: September 23, 2026

What is the difference between contact forces and non-contact forces?
Contact forces, such as friction or muscular force, require direct physical contact to act, while non-contact forces, such as gravitational or magnetic force, can act on an object even from a distance without touching it.

Written by Satish

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