Dynamics

What these notes cover

These notes cover dynamics for Cambridge International AS Level Physics (9702): Newton’s laws of motion, linear momentum and impulse, the principle of conservation of momentum, and elastic and inelastic collisions. They show how to apply conservation of momentum to collision problems.

Key formulas and definitions

• Newton’s first law: an object stays at rest or moves with constant velocity unless a resultant force acts on it.
• Newton’s second law: the resultant force is equal to the rate of change of momentum, F = Δp / Δt; for constant mass, F = ma.
• Newton’s third law: if body A exerts a force on body B, then B exerts a force on A that is equal in magnitude, opposite in direction and of the same type.
• Linear momentum: p = mv (a vector; unit kg m s⁻¹, equivalent to N s).
• Impulse = FΔt = change in momentum.
• Conservation of momentum: for a system with no resultant external force, the total momentum before an interaction equals the total momentum after it.
• In an elastic collision, total kinetic energy is conserved and the relative speed of approach equals the relative speed of separation. In an inelastic collision, some kinetic energy is transferred to other forms (total energy is still conserved).