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What is impulse (I)?

Impulse is the product of force (F) and the time (t) over which the force acts (I=Ft). With that being said, when a force is applied to an object, the resulting motion of the body is dependent not only on the magnitude of the force but also on the duration of the force application. Therefore, an object can be set in motion by applying a large force over a relatively short period of time or a small force over a relatively long period of time. Both of these impulses can create motion in an object, but what is more effective at producing motion in sports.

One of the most common examples of impulse in sports is the volleyball player who jumps up to spike a ball during a match. Theoretically, the volleyball player has two options. Option number one, the volleyball player could apply a relatively small force over a longer time frame to produce an impulse. Option number two, the same volleyball player could apply a large force over a relatively short period of time to produce the exact same impulse. However, in theory this makes sense, but when it is put into practice, the volleyball player who choses option two will generate more vertical velocity and has a much higher jump height. In sports or activities which require more “explosive movements” a large force applied over a short time frame will produce a much better result. Another example of this is a hockey player attempting to take slap shot. The hockey player can produce a much harder shot if the force is applied to the puck over a very short period of time (ie. the less time the puck is on the stick, the harder the shot).

With that being said, there are several examples in sports where it is important to produce less impulse. For example, a hockey player receiving a pass or baseball player receiving a ground ball will want to allow the time of force application to be increased in order to decrease the force with which the object is received. This is done by cushioning the pass or grounder. A hockey player is taught to have soft hands and allow the puck to hit the stick and absorb the puck. This motion allows the force to be absorbed over a longer period of time, thus decreasing the overall impulse. Have you ever heard you coach say that receiving a pass should be “quiet”? In the baseball example, the fielder will absorb the force of the ball by bringing the hands into the body and transitioning it into a throw. The longer time spend absorbing the force, the less the impulse which will be applied to the glove and hand. This principle can help ease the pain of the baseball player who catches the ball in the palm of the glove without allowing time to absorb the ball.

Check back next week for more in Linear Motion and Principle #5!

Thanks,
Brian Shackel, MSc