Physics
Newton's laws of motion
Inertia, F=ma, action–reaction — the three laws all of mechanics rests on.
Newton's three laws are the foundation of classical mechanics.
Walk through
Step 1 of 4
1st law — inertia
No net force? Then no change in motion. A puck on frictionless ice glides forever; you only feel 'thrown forward' in a braking car because *you* keep moving while the car slows.
Newton's second law
Force in newtons (N), mass in kg, acceleration in m/s². 1 N is the force that accelerates 1 kg at 1 m/s².
Your turn
A 1500 kg car accelerates at 2 m/s². What net force drives it?
Watch out
The action–reaction pair acts on two different bodies — they never cancel each other. The forces on a *single* object are what you add to get the net force.
The three laws
- 1st (inertia) — an object stays at rest or in uniform motion unless a force acts on it.
- 2nd — F = ma. Force equals mass times acceleration.
- 3rd — for every action there's an equal and opposite reaction.