The Unit Circle is a circle with a radius of 1. The unit circle identifies coordinates by using the angles of sine, cosine, and tangent. The image below is an example of the unit circle:

###### source

The sine of an angle in a video game tells us that the motion is changing for y axis. So this means that an object when in motion is changing by the y axis.

The cosine of an angle in a video game tells us that the motion is changing for the x axis.

The sine and cosine of an angle helps give the coordinates of an image because they give where the x and y coordinates are.