Newton's Laws of Motion

Newton's three laws of motion form the foundation of classical mechanics. They describe the relationship between forces acting on an object and the motion of that object. Every mechanics problem you encounter at A-Level can ultimately be traced back to these three laws.

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Newton's First Law (The Law of Inertia)

An object remains at rest or continues to move at constant velocity unless acted upon by a resultant (net) force.

This law tells us two things:

1. A stationary object stays stationary unless a net force acts on it.
2. A moving object continues at the same speed in the same direction unless a net force acts on it.

The key word is resultant. An object can have many forces acting on it, but if they all cancel out (resultant = 0), the object behaves as if no force is acting. A book on a table has weight pushing it down and a normal contact force pushing it up — these balance, so the book stays still.

Inertia is the tendency of an object to resist changes in its motion. Mass is a measure of inertia — a more massive object is harder to accelerate or decelerate.

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