Newtons First Law – GCSE Physics

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Introduction

  • Motion is the change in position of an object with respect to time.
  • Newton’s First Law of Motion explains how objects behave when no external forces act on them.
  • An object in motion stays in motion with the same Speed and same Direction unless an External Force act on it.

Examples:

Two examples of Newton's First Law: a sudden brake in a car, and a ball at rest on the ground.

Two examples of Newton's First Law: riding on a swing and standing in a moving bus, illustrating motion and inertia.

What is Newtons First Law of Motion?

  • It States that a Resultant Force is required to change the Motion of an object.
  • Newtons First Law of Motion is also called Inertia because it describes the concept of Inertia which is,

The Natural tendency of an objects to Resist changes in their state of Motion.

Examples:

  • A satellite in space continues moving unless acted upon by gravity.

newton's law about gravity

  • The ketchup stays at the bottom until the force overcomes its inertia.

An elderly man applying force to a ketchup bottle, demonstrating Newton's First Law where an object at rest (the ketchup) stays at rest until acted upon by an external force.

  • A bike stays balanced while moving.

A motorcycle in motion on a curved road, demonstrating Newton's First Law where an object in motion stays in motion unless acted upon by an external force.

What are Balanced and Unbalanced Force?

Balanced Force:

  • Forces acting on an object are equal in Magnitude but opposite in Direction.
  • They cancel each other out, so the Resultant Force is Zero.

Characteristics:

    • No change in Motion.
    • Object or Body remains at rest or continues at Constant Velocity.

Examples:

Unbalanced Force:

  • Forces acting on an object are not equal in Unbalanced Force.
  • They do not cancel each other out, so the Resultant Force is non-zero.

A formula showing the situation where the resultant force (FR) is not equal to zero, indicating an unbalanced force.

Characteristics:

  • Change in Motion.
  • Object or Body accelerates (speed up, speed down or change direction).

Examples:

Real-life Examples

  • A rolling soccer ball slows down and stops because Inertia keeps it moving, but friction and air resistance act as external forces to stop it.

A soccer ball at rest on the field, illustrating Newton's First Law of Motion where an object at rest stays at rest unless acted upon by an external force.

  • When we beat a carpet, dust particles fall out because the carpet moves, but dust tends to stay at rest until gravity pulls it down.

A man swinging a stick at an object, demonstrating Newton's First Law where an object at rest stays at rest until acted upon by an external force.

  • In a collision, seatbelts prevent passengers from flying forward.

A person fastening a seatbelt in a car, demonstrating Newton's First Law where an object in motion will continue in motion unless acted upon by an external force.

Frequently Asked Questions

Solution:

It means that an object will keep doing what it’s doing – moving or staying still — unless a force changes that.

Solution:

It means that a moving object will keep going at the same speed and in the same direction unless something like friction or another force slows it down.

Solution: 

Balanced forces don’t change motion. Unbalanced forces cause an object to speed up, slow down, or change direction.

Solution:

It’s seen when a car stops suddenly, and passengers jerk forward — their bodies want to keep moving because of Inertia.

Solution:

Gravity is a force, and Newton’s First Law explains how forces like gravity can change an object’s motion. So, Gravity can act as the external force mentioned in the law.

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