- By integrating over time both sides of Newton’s second law , we create the concept called impulse

- If the force is constant, we have

- Alternatively, we can work with the average force <
*F*>,

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- We can infer from the change in momentum of a body (over a period of time) the impulse acting on the body (over that period of time).

|Δ*p|* = (2)(3) – (2)(-3) = 12 kg m s^{-1}

- In the above elastic collision, the wall exerted a leftward impulse of 12 N s on the ball, while the ball exerted a rightward impulse of 12 N s on the wall.
- Assuming the duration of impact to be 0.2 s, the average force acting on the ball during the impact would have been 12 ÷ 0.2 = 60 N.

|Δ*p|* = (2)(3) – 0 = 6 kg m s^{-1}

- In comparison, in the above completely inelastic collision, the impulse between the wall and the ball is only 6 N s.
- Assuming the duration of impact to be 0.2 s, the average contact force would have been 6 ÷ 0.2 = 30 N.

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Demonstrations

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