The effect of force acting over a certain time can be represented by the derived quantity impulse. It is the product of force and the time interval over which the force is applied. It is a vector quantity having the same direction as that of the force applied. It is expressed as vector J, and the SI unit is the newton-second. If a graph is plotted between the net force and time, then impulse is given by the area under the curve, which is the definite integral of the force function over a time interval. For instance, in golf, the ball experiences a large impulse during a slap shot. A huge force acts on the ball for less than a second which causes a change in the velocity of the ball. The impulse of a large force acting over a shorter duration of time can be similar to that of a small force acting for a longer duration of time. For instance, the impulse involved in stopping a truck either by sudden braking or by braking gently over a longer period of time would be similar.