Applying Newton's Laws

This lesson covers the practical application of Newton's three laws of motion, particularly F = ma, to real-world problems — as required by the Edexcel GCSE Physics specification (1PH0), Topic 2: Motion and Forces. You need to be able to apply F = ma to a range of situations, understand inertial mass, and describe the core practical investigating force, mass and acceleration.

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Newton's Three Laws — Quick Recap

Newton's First Law

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

• No resultant force → no change in velocity (object stays still or moves at constant speed in a straight line).
• This is the law of inertia — objects resist changes to their motion.

Newton's Second Law

The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass:

F = m × a

Quantity	Symbol	Unit
Resultant force	F	Newtons (N)
Mass	m	Kilograms (kg)
Acceleration	a	Metres per second squared (m/s²)