Newton's Laws of Motion

This lesson covers all three of Newton's laws of motion as required by the AQA GCSE Physics specification (4.5.6). Newton's laws describe how forces affect the motion of objects and are fundamental to understanding all aspects of mechanics. You must be able to state each law, explain it with examples, and apply it to calculations.

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Newton's First Law

Newton's first law states:

An object will remain at rest or continue to move at a constant velocity unless acted upon by a resultant (unbalanced) force.

What This Means

• If the resultant force on an object is zero, the object either:
  • Stays stationary (if it was already stationary), or
  • Continues to move at a constant velocity (same speed, same direction).
• If the resultant force is not zero, the object will accelerate (change its speed or direction).

Inertia

Inertia is the tendency of an object to resist a change in its motion. An object with more mass has more inertia — it is harder to start moving, harder to stop, and harder to change direction.