24 October 2011

A Physical Approach

And no, I'm not suggesting ways of getting out of traffic fines. After a talk given by Dan at the Kunjani'mation workshops, it became obvious that a solid grounding in physics (the basics, not the fiddly quantum bits) will go a long way to improving anyone's animation skills!

Today's post is for animators, so if you like to come here to look at the pictures you are welcome to look at older posts with less blahblahblah in them :D

So I picked up an e-book from a friend, Conceptual Physics, which is available under a creative commons license. Soon after reading the first chapter I realised I've been thinking about overlap and follow-through quite, well, wrong. (That, and preservation of energy in a bouncing ball, but I'll save that for a later post.)

So, I did some tests: a mass accelerates, reaches a constant speed, then stops. With a dangly thing underneath. I know, very animation mentor. Sue me.

The video below shows a common misconception (one I've held as a rule of thumb since I started animating): The faster an object  is going, the more drag there will be in it's dangly bits. Sounds pretty believable, right? Wrong, because of the principle of inertia!



This next video illustrates the more physically accurate pendulum. According to the principle of inertia, one frame of reference can only be measured relative to another, and that without this frame of reference no motion is actually happening (kind of trippy, eh?). My point being, when you jump up, the world(the surface of which is moving at 400m/s relative to it's centre) does not slip away under your feet. You land in the same spot. You appear to be in the same spot, but actually the ground has imparted you with the complementary initial velocity of 400m/s! This is the same reason that an unfastened seatbelt will send you flying through the wind shield of a car that suddenly stops, but if the car keeps a constant speed, it is quite possible to juggle balls normally, given sufficient elbow room.



So, the way this applies to overlap in animation is this: Acceleration and deceleration cause the overlap and follow through, but when the object has reached a cruising speed, objects attached to it will come to rest, relative to the object itself(affected to varying degrees by air resistance and other kinds of friction, say, an inconveniently positioned metro-cop). And of course, none of this would work without gravity, so I reckon applying this rule to your animation will go a long way to improving that sought after illusion of weight!

And yes, I did get a ticket today at a roadblock. No, I wasn't drunk. Yes, my passenger side seat belt was broken, and no, it wasn't far to give my friend a lift to the station, nor was he juggling.

Yes, I will get it fixed officer.

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