An object at rest stays at rest. An object in motion stays in motion at the same speed and direction — unless an external net force acts upon it. This property is called inertia.
Real world → A hockey puck slides forever on a frictionless ice rink. Seatbelts exist because your body wants to keep moving when the car stops.
Second Law — Law of Acceleration
F = ma ⟺ a = F/m
Net force equals mass × acceleration. Greater force produces greater acceleration. Greater mass requires more force for the same acceleration. This is the quantitative heart of classical mechanics.
Real world → Rocket engines produce thrust to accelerate a spacecraft. A heavier car needs a bigger engine. F1 cars use low mass + extreme force for insane acceleration.
Third Law — Action & Reaction
F₁₂ = −F₂₁
For every action there is an equal and opposite reaction. Forces always come in pairs. When block A pushes block B, B pushes back on A with the same magnitude but opposite direction.
Real world → Rockets work in space: hot gas is expelled backward (action), rocket moves forward (reaction). Walking — your foot pushes Earth back; Earth pushes you forward.
⚗ Experiment Protocol
01
Set Force = 0, Friction OFF → Start. Observe no motion (Law I: zero net force).
02
Set Force = 10N → Start. Watch the block accelerate smoothly.
03
Double the mass → Reset and Start. Acceleration halves (a = F/m).
04
Enable Friction → See how it opposes motion and reduces net force.
Physics Engine — Real-time Simulation
IDLE
Mass2 kg
Applied Force5 N
Friction Coeff. (μ)0.30
Friction
μmg = kinetic drag
Position
0.00
meters
Velocity
0.00
m/s
Acceleration
0.00
m/s²
Net Force
0.00
newtons
🔭
Adjust parameters and press Launch to begin the simulation.