Review These For Information Regarding Momentum and Impulse:
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Momentum
Momentum is a quantity that describes the motion of a particle. It can be found by taking the product of the mass of the object times its velocity:
p = mv
The Law of Conservation of momentum describes an important facet of physics: if two objects in an isolated system collide, the total final momentum of both objects is equal to the total initial momentum of both objects.
Impulse
Impulse is defined as the overall effect of a force over time. This can then be equated to the change of momentum. It can be calculated by taking the product of the force times the elapsed time:
Δp =
When running, the foot hits the ground, causing a Newton’s Third Law pair to exert a push the body upwards.
When wearing shoes, the change in momentum (impulse) can be impacted on how the shoe is designed.
If the shoe has a very padded sole, the elapsed time over which the force is exerted on the body is lengthened. This decreases the force necessary to produce the same change in momentum:
Think of dropping an egg on a hard surface versus a pillow, the egg will not break on the pillow because of this same principle.
The opposite effect is produced by having a very thin sole (or not wearing any shoes at all).
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Benefits of Increased Time of Force Application
By increasing the time during which the force is exerted, the force on the body is lessened. This decrease in the force on the body leads to less wear-and-tear on the body, leading to less injury. The knees, for example, experience less impact and thus will stay in better condition throughout life.
Downsides of Increased Time of Force Application
While reducing the chance of injury seems like an important idea, excessive cushioning in a sole leads to heavier shoes. This makes running fast more difficult, as the body needs to carry heavier weight. Additionally, the lower magnitude of force exerted on the body causes a less “explosive power,” by the runner leading to less quick running. That is why many racers wear lightweight thin shoes, such as spikes or racing flats to reduce weight and increase the upwards force.
