The seatbelt lesson
When a car stops fast, your body keeps moving forward until the seatbelt pushes back — that's inertia and Newton's laws in one jolt. Objects keep doing what they're doing until a force says otherwise, and every push comes with an equal push back.
Three laws
- 1st: an object stays at rest or in motion unless a force acts (inertia)
- 2nd: F = ma — force equals mass times acceleration
- 3rd: every action has an equal and opposite reaction
A 2 kg cart pushed with 10 N: a = F/m = 10/2 = 5 m/s²
Simulation · Newton's second law: F = ma
a = F / m = 5.0 m/s²
Set a force and a mass, then apply the force. More force speeds the block up; more mass slows it down.
Lab · Heavier vs. lighter
- Set force to 20 N and mass to 2 kg. Apply the force and note how quickly the block crosses.
- Keep the force at 20 N but raise the mass to 10 kg. Apply again.
- Compare the acceleration values shown.
What you should see: With the same force, the heavier block accelerates less (a = F/m). Doubling mass halves the acceleration.