This assignment's purpose was to introduce the concept of motion blur. You ask, what is motion blur? Motion blur is the existence of "ghost images", when an object is in motion. This is actually quite a simple effect to achieve. When we are ray tracing our scene, we assign a time to each ray, when then attempts to intersect itself with the scene. This time value has no affect on non-moving objects, since they merely ignore it. Those objects that are moving, use this time to recalculate their position in the scene.

 

This image is of two sphere's and the back sphere, I've set to have a shutter interval of 0.15 seconds. I've also told it that it needs to travel 1/2 the distance across the floor in 1 second. You can then notice the shutter bands produced in the image.