Sports Physics 101

Speed is the rate of movement over a distance. In sport it is often desirable to go fast, that is, to have a high speed. For our purposes the terms speed and velocity, and distance and displacement can be interchanged.

Velocity is calculated by this equation:

Velocity = Displacement/Time

The standard metric unit of velocity is metre/second.

Acceleration is the rate of change in velocity.

Acceleration = Force/Mass

• The standard metric unit of acceleration is metre/second/second.
• The standard metric unit of force is the Newton.
• The standard metric unit of Mass is the kilogram.

In physics, work is defined as a force acting upon an object to cause a displacement. There are three key words in this definition - force, displacement, and cause. In order for a force to qualify as having done work on an object, there must be a displacement and the force must cause the displacement. There are several good examples of work that can be observed in sporting life - a weightlifter lifting a barbell above her head, an Olympian launching the shot-put, a rugby player shoving an opponent out of the way, etc. In each case described here there is a force exerted upon an object to cause that object to be displaced.

The quantity of work has to do with a force causing a displacement. Work has nothing to do with the amount of time that this force acts to cause the displacement. Sometimes, the work is done very quickly and other times the work is done rather slowly. For example, a rock climber takes a relatively long time to elevate his body a few metres up a cliff. On the other hand, a bush walker (who selects the easier path up the mountain) might elevate her body a few meters in a short amount of time. The two people might do the same amount of work, yet the bush walker does the work in considerably less time than the rock climber. The quantity which has to do with the rate at which a certain amount of work is done is known as the power. The bush walker has a greater power rating than the rock climber.

Power is the rate at which work is done. It is the work/time ratio. Mathematically, it is computed using the following equation.

Power = Work/ Time

The standard metric unit of power is the Watt. As is implied by the equation for power, a unit of power is equivalent to a unit of work divided by a unit of time. Thus, a Watt is equivalent to a Joule/second.

So from the sports point of view, strength is the ability to apply force. A strong person can apply a large force enabling them to lift a heavy weight or push a heavy object out of the way.

There are many sports however, where force needs to be applied quickly to either develop high accelerations or to fend off an opponent. In these sports the strong athlete with a high power rating has the advantage. It is possible to use weights training to improve an athlete’s strength and power rating.