The Biomechanics of Skating: Linear Dynamics

Getting Started

Before you begin this Unit, it is helpful to have worked through the kinematics unit. In the following applications you will be doing calculations, so have the following materials handy: pencil, paper, calculator, transparency, tape and non-permanent pen. We will be working in the metric system. If necessary, review the units: meters, seconds, kilograms, newtons, etc.

Newton’s Second Law

Forces

What is meant in physics by a force? Briefly, a force on an object is a push or pull that comes about because the object interacts with the rest of the world (that is, other objects).

A force is a vector quantity since it has a size and a direction. (see vector applications in the kinematics unit.) It is measured in Newtons, abbreviated:

For instance, the earth’s gravity pulls vertically downward on the luge. This force is proportional to the mass of the luge and is called the luge’s weight. On the earth’s surface, the weight (in Newtons) is equal to the mass (in kilograms) times...

...a quantity that is usually written “g” and called the “gravitational acceleration”.

Mass and weight are not the same thing (one is measured in kilograms, the other in Newtons), but they are proportional to each other. This is because the gravitational attraction between any two objects (like the earth and the slider) is proportional to the mass of each of them. So, for example, doubling the mass of the slider doubles the gravitational force -- that is, doubles the slider’s weight.