Summary 429 mOmentum Understanding what momentum is and how it works is pretty important for an animator. When an object is in motion, it has momentum. The amount of momentum is calculated by multiplying the mass of the object by its velocity. The heavier something is, or the faster it is moving, the more momentum it has and the bigger the bruise it will leave if it hits you. That's why a tiny bullet can cause such a great impact on a can of stew, for example. Its sheer speed greatly increases its momentum. Likewise, a slow-moving dump truck can bash in your car, relying on its sheer mass for its tremendous momentum. Basically, when one moving object meets another object that is moving or not, momen- tum is transferred between them. That means when something hits an object, that target is somehow moved if there is sufficient momentum transferred to it. It follows that the more mass an object has, the more momentum will transfer to the target. Also, the more velocity an object has, the more momentum will be transferred to the target on collision. You will be able to show the mass of an object in animation by showing how much momentum it transfers when it impacts another object. This could be as simple a as knife hitting a target and moving it back, as you animated in the exercise in this chapter, or as complicated as a heavyset man walking down the street. In the latter case, because the pavement can't give way underneath the man, the momentum that is transferred is reflected back to the man and absorbed by his body. That makes his body bend and flex and his big belly jiggle up and down with each step. Impact is a perfect opportunity for an animator to show his subject's mass in motion, and it is always intrinsic in good animation. You can see a sample render of the scene in the knife_animation.mov QuickTime file in the RenderOutput folder of the Knife project on the companion web page (or copied onto your hard drive). You can also download the Animation_Knife_01.max scene file from the Scenes folder of the Knife project to check your work. Introducing Maya 2011 (Wiley, 2010) includes an ax-throwing exercise that teaches the same kinds of animation concepts as the knife-throwing exercise in this chapter. Check it out if you are curious about how 3ds Max and Maya animate similar scenes. Summary In this, the first of two chapters on animation, you learned the basics of creating and edit- ing animation. You learned about hierarchies and how to link objects together to create a hierarchy useful for our mobile animation as well as how pivot points are used. You also learned how to create animation using the Auto Key function.