### Impulsive Force

- Impulsive force is defined as the rate of change of momentum in a reaction. Mathematically, we write $$F=\frac{mv-mu}{t}$$
- It is a force which acts on an object for a very short interval during a collision or explosion.

**Example**:

A car of mass 1000kg is traveling with a velocity of 25 m/s. The car hits a street lamp and is stopped in0.05 seconds. What is the impulsive force acting on the car during the crash?

**Answer**:

m = 1000kg

u = 24 m/s

v = 0

t = 0.05s

$$\begin{array}{l}F=\frac{mv-mu}{t}\\ F=\frac{(1000)(0)-(1000)(24)}{0.05}\\ F=480,000N\end{array}$$

Effects of impulse vs Force

- A force determines the acceleration (rate of velocity change) of an object. A greater force produces a higher acceleration.
- An impulse determines the velocity change of an object. A greater impulse yield a higher velocity change.

- Playing football
- Playing badminton
- Playing tennis
- Playing golf
- Playing baseball

#### Long Jump

- The long jump pit is filled with sand to increase the reaction time when atlete land on it.
- This is to reduce the impulsive force acts on the leg of the atlete because impulsive force is inversely proportional to the reaction time.

#### High Jump

(This image is licenced under the GNU Free Document Licence. The original file is from the Wikipedia.org.)

- During a high jump, a high jumper will land on a thick, soft mattress after the jump.
- This is to increase the reaction time and hence reduces the impulsive force acting on the high jumper.