JAMB UTME Prep•13 Sept 2026• 4 min read

Newton's Laws of Motion for JAMB Physics – Full Breakdown

Understand Newton's Laws of Motion for JAMB Physics with simple explanations and worked examples — the way they actually show up in JAMB questions.

Newton's Laws of Motion are three rules that explain how and why objects move the way they do — and JAMB tests all three regularly, often with calculation-based questions. Here's exactly how they show up and how to solve them.

What Are Newton's Laws of Motion?

Sir Isaac Newton formulated three laws that describe the relationship between a body and the forces acting on it, and how the body responds to those forces. These three laws form the foundation of classical mechanics, and JAMB Physics tests both the concepts and the calculations that come from them.

How JAMB Tests This

JAMB Physics typically tests Newton's Laws through:

Conceptual questions — identifying which law explains a given scenario
Force calculations — using F = ma to solve for force, mass, or acceleration
Action-reaction pairs — identifying the reaction force in a given situation

Newton's First Law (Law of Inertia)

An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted on by an external force.

This is also called the Law of Inertia — inertia being an object's resistance to a change in its state of motion. A heavier object has more inertia, meaning it's harder to start moving or stop once moving.

Real-world example: A passenger in a car jerks forward when the car suddenly stops — their body was in motion and resists the sudden change, until the seatbelt (an external force) acts on them.

Newton's Second Law (F = ma)

The acceleration of an object is directly proportional to the net force acting on it, and inversely proportional to its mass.

This is expressed as the formula:

F = ma

Where:

F = force (measured in Newtons, N)
m = mass (measured in kilograms, kg)
a = acceleration (measured in metres per second squared, m/s²)

This is the law JAMB tests most often through direct calculation.

Worked Example 1: Using F = ma

A force of 20N acts on an object of mass 4kg. Calculate the acceleration produced.

Step 1: Write the formula: F = ma

Step 2: Rearrange to solve for acceleration: a = F/m

Step 3: Substitute values: a = 20/4

Answer: a = 5 m/s²

Worked Example 2: Solving for Mass

A force of 50N produces an acceleration of 10 m/s² on an object. Find the mass of the object.

Step 1: Write the formula: F = ma

Step 2: Rearrange to solve for mass: m = F/a

Step 3: Substitute values: m = 50/10

Answer: m = 5 kg

Newton's Third Law (Action and Reaction)

For every action, there is an equal and opposite reaction.

This means forces always occur in pairs — when object A exerts a force on object B, object B exerts an equal and opposite force back on object A.

Real-world example: When you jump off the ground, your legs push down on the ground (action), and the ground pushes back up on you with equal force (reaction) — this is what propels you upward.

Try It Yourself

A force of 15N acts on a 3kg object. Find the acceleration.
What law explains why a rocket moves forward when it expels gas backward?
A 2kg object accelerates at 4 m/s². What force is acting on it?

Answers:

a = F/m = 15/3 = 5 m/s²
Newton's Third Law — the rocket expelling gas backward (action) produces an equal and opposite force pushing the rocket forward (reaction)
F = ma = 2 × 4 = 8N

Common Mistakes to Avoid

Forgetting to convert units before calculating (e.g., mass given in grams must be converted to kg before using F = ma)
Mixing up which law applies to which scenario — First Law is about resistance to change, Second Law is about calculation, Third Law is about paired forces
Forgetting that action-reaction pairs act on two different objects, not the same object

Continue practicing with our JAMB Physics past questions or explore common mistakes students make in JAMB Physics. For the full subject breakdown, visit the JAMB Physics guide.