| English | Impulsive force |
|---|---|
| Bahasa Melayu | Daya impuls |
| 中文 | 冲力 |
Definition
The large force acting over a very short time during a collision or explosion (impulsive force = change in momentum ÷ time).
In exam terms
An impulsive force is the large force that acts over a very short time during a collision or explosion. It is calculated from impulsive force = change in momentum ÷ time, or F = (mv − mu) ÷ t, and is a vector measured in newtons (N).
Because the contact time is tiny, the force is very large. For example, if a 0.5 kg ball hitting a wall changes its momentum by 6 kg m s⁻¹ in 0.02 s, the impulsive force = 6 kg m s⁻¹ ÷ 0.02 s = 300 N. Increasing the contact time reduces this force for the same momentum change.
Do not confuse it with…
Do not confuse impulsive force with impulse. Impulsive force (N) is the size of the force during the brief contact, while impulse (N s) is the total change in momentum.
They are linked by impulse = impulsive force × time.
In Paper 2 this is a common explain question: why do padded dashboards, thick gloves or bending your knees on landing reduce injury? State that they lengthen the contact time, and since the momentum change is fixed, a longer time means a smaller impulsive force acting on the body.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)