| English | Impulse |
|---|---|
| Bahasa Melayu | Impuls |
| 中文 | 冲量 |
Definition
The product of a force and the time for which it acts, equal to the change in momentum it produces; measured in newton seconds (N s).
In exam terms
Impulse is the product of a force and the time for which it acts. It equals the change in momentum it produces, so impulse = F t = mv − mu.
Its SI unit is the newton second (N s), which is equivalent to kg m s⁻¹, the same unit as momentum.
Impulse is a vector, taking the direction of the force. For example, a 20 N force acting on a ball for 0.5 s gives an impulse = F t = 20 N × 0.5 s = 10 N s, so the ball's momentum changes by 10 kg m s⁻¹ in the direction of the force.
Do not confuse it with…
Do not confuse impulse with impulsive force. Impulse (N s) is the whole change in momentum, while impulsive force (N) is how large the force is during the short contact time (impulsive force = change in momentum ÷ time).
A longer contact time gives the same impulse but a smaller impulsive force.
In Paper 2 you may be asked to define impulse, or to explain how a crumple zone or a soft landing reduces the impulsive force. State that the impulse (momentum change) is fixed, so increasing the time reduces the force felt.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)