There are two teaching approaches to Newton’s second law used in early physics teaching:
- the approach through using forces to produce acceleration with different masses leading to F ∝ ma
- the approach through momentum and force x time = change of momentum (in symbols Ft = Δmv ), which was Newton’s choice.
Students often confuse energy and momentum. It may help for teachers to have at the back of their minds, when introducing these ideas, that change of energy is the space integral (ΔE = ∫ F ⋅ Δs) and change of momentum is the time integral (Δmv = ∫ F ⋅ Δt).