Free body diagrams (otherwise known as FBD's) are simplified representations in a problem of an object (the body), and the force vectors acting on it. This body is free because the diagram will show it without its surroundings; i.e. the body is 'free' of its environment. This eliminates unnecessary information which might be given in a problem. 

Let's take this figure to be a pictorial representation of our problem: a sled on snow, with horses pulling it. First we will represent the sled (the 'body' in our problem) as a (really) simplified figure, a square resting on a flat surface.

In this tutorial, we will review some of the main forces which you will encounter in physics, and discuss their contribution to an FBD. 

·Gravity

·Normal Force

·Friction 

·Push or Pull