Newton's Laws of Motion
Year 9 🚀 Forces & Motion State and apply all three of Newton's laws with examples.
🍎 Newton's First Law
An object remains at rest or moves with constant velocity unless acted upon by a resultant force. This is the law of inertia.
Example: A book on a table stays still. A rolling ball on a frictionless surface keeps rolling forever.
When a car brakes suddenly, passengers lurch forward — their bodies try to continue at the original velocity (inertia).
⚡ Newton's Second Law
The resultant force on an object equals its mass times its acceleration. Force, mass and acceleration are all related.
⚡ Newton's 2nd Law
$$F = ma$$
$F$ = resultant force (N) · $m$ = mass (kg) · $a$ = acceleration (m/s²)
Example: A 5 kg box accelerates at 3 m/s² → F = 5 × 3 = 15 N
🔄 Newton's Third Law
For every action there is an equal and opposite reaction. Forces always act in pairs on different objects.
Example: You push the ground down (action) → the ground pushes you up (reaction) — this is what lifts you when you jump!
Ready to test yourself? Click the Quiz tab above to answer questions on this topic!
⚡ F = ma Calculator