Timing
Timing and Motion are tied together because in animation the two are basically the same thing. Change the time that it takes a character to complete an action and it will change it's motion.
Timing is interested in how fast an action is happening. This will tell a lot about the mass of an object. If someone lifts up a bowling ball they will do it much slower then they would if they picked up a basketball the two actions could be accomplished using the same motion just different timing. If a character walks sluggishly it would seem like he is walking in water.
Timing can tell about the emotions of a character.
If a character swings his head from left to the right in almost no time then he has been hit by some strong force that nearly takes his head off.
Slow that same action down and you have the character getting hit by a fist.
Just a little slower and the character quickly snaps his head to the right because he heard a sound in the woods.
A little slower and he can be moving his head back and forth to the beat of a good song
Really slow and he could be stretching some sore muscles from doing homework all day. This can all be done with the same action.
The timing gives some idea as to the forces involved in movement and the mass of an object take for example the animations shown below (animations form www.siggraph.org/education)
In the First animation the ball bounces off of the box. Conservation of momentum tells us that the box is heavier than the ball. In the second animation we can see that the box is much lighter than the ball because the ball has almost no change in momentum at all while the box is moved to a new location.
