Newton's Laws of Motion

This lesson covers Newton's three laws of motion — as required by the Edexcel GCSE Physics specification (1PH0), Topic 1: Key Concepts of Physics. You need to be able to state, explain, and apply each of the three laws to a variety of situations.

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Newton's First Law

Newton's First Law: An object will remain stationary or continue to move at a constant velocity unless acted upon by a resultant force.

What Does This Mean?

• If an object is stationary and no resultant force acts on it, it stays stationary.
• If an object is moving and no resultant force acts on it, it continues to move in a straight line at constant speed.
• A resultant force is needed to change an object's velocity — to make it speed up, slow down, or change direction.

Inertia

Inertia is the tendency of an object to resist a change in its state of motion. It is directly related to mass — the greater the mass, the greater the inertia, and the harder it is to change the object's motion.