Physics (4PH1)
Inertia: Object stays still or constant velocity unless a resultant force acts. F = ma: More force → more acceleration; more mass → less acceleration. Action-reaction: Equal and opposite forces on different objects.
Topic 1 of 1Pearson EdExcel
Forces and Motion
Speed, acceleration, and Newton's laws
Speed = Distance ÷ Time (S = D/T). On a distance-time graph, gradient = speed. Horizontal line = stationary.
Acceleration = (Final velocity − Initial velocity) ÷ Time (a = Δv/t). Units: m/s². On a velocity-time graph, gradient = acceleration; area under graph = distance.
Newton's Laws:
Momentum = Mass × Velocity** (p = mv). **Conservation of momentum: total momentum before collision = total after (closed system).
Key Points to Remember
- 1Speed, distance, time calculations
- 2Acceleration and deceleration
- 3Newton's three laws
- 4Momentum conservation
Pakistan Example
M-2 Motorway — Speed and Stopping Distance
At 120 km/h on the M-2, a car travels over 23 metres before brakes are applied (thinking distance). Newton's Second Law explains why heavy trucks need longer to stop — greater mass means less deceleration from the same braking force.