Sidenote: Here's a more reader friendly version.
One of the animator’s goals is to make the animation believable in the eyes of the viewer. An example of that is that the emotion portrayed needs to look sincere. Another is that the animation needs to abide the laws of physics of the world it’s in. I’ll be talking about the latter, about technically correct, consistent, animation, physics and whatnot.
This might sound a bit daunting to the beginning animator, but it’s actually just some general rules that you need to keep in mind. The rules are easy, but they are easily overlooked and sometimes harder to implement. My own goal with this piece of text is to provide you all with a teeny bit of awareness, and I hope that will make your animations that much better.
Also worth looking into: Suspension of disbelief
Intro to consistency
Maybe I'm just a geek, but I like consistency. I like the fact that if you know the weight of an object, you can calculate the time it takes for it to reach the ground from a certain height (leaving density and air friction out of the equation). I like the fact that when a ball bounces (up/down), it will leave the ground with the same speed that it approached the surface (provided that the surface is flat, inanimate and isn't sticky).
I like the consistency, the predictability, the logic. I like the fact that if you follow certain rules and logic, your animation will have a higher chance of being convincing, isn't that just great? Reading this piece is but a small price to pay for becoming aware of such logic, right?
Okay! So we've established that I'm a geek, but have I convinced you of the importance of consistency in animation? I bet not! Next up I'll cover some of the bases you need to cover when working on an animation and I'll add examples to the mix too. I'll not hand every bit of knowledge to you on a silver platter though, if you don't understand something try to research it or ask questions, try to truly understand it! Good luck! :)
(Exceptions to these pieces of logic are dealt with later on in the article.)
Gravity / Weight
I'll spare you the big scientific explanations, but here are just some basics you need to be aware of.
Gravity is a force that acts on anything that has a weight and a volume. Gravity is "a natural phenomenon by which physical bodies attract each other with a force proportional to their masses" (according to Wikipedia).
Seeing as the mass of a planet is a constant, it depends on the mass of an object what the gravitational effect will be (the heavier the object, the bigger the force will be).
During an animation, the mass of the object and the planet won't change, they are both consistent. The force between the object and planet will be consistent! Exceptions aside, gravity and weight are predictable and consistent. They won't suddenly change unless there's a third party in play. (Like a magnet, a huge blowing fan or addition of helium).
EXAMPLE: Anatomy of a bouncing ball (part 1)
This is the exercise that every animator has to do, for a very good reason, but unfortunately not every animator is confronted with the truth behind this. Did you ever try to understand the logic behind the bounces? What makes the bounces get smaller? How fast do the bounces get smaller?
Did you ever notice that the arc of each bounce has the same width/height aspect ratio? That they get proportionally smaller?
It's all about gravity! Gravity is the steady force that attracts the ball to the ground. Gravity is steady, that means that with each bounce, the bounces get proportionally smaller, proportionally being another key word here related to consistency!
EXAMPLE: Floatiness, a problem that pretty much all of us animators have encountered at one point or another. So if you get this critique on 11secondclub or from your peers, this is what it means: the problem is that during the animation, the object seems to be able to stay in the air longer than its weight and force should allow. It's not consistent with what we expect. It's not consistent with the weight of the object or with the force (whether it be gravity or other).
This might also occur the other way around, the object seems to be in the air shorter than its weight should be able to allow.
EXAMPLE: a more problematic encounter with floatiness:
A while back I saw an animation of a balloon filled with helium. The balloon is let go, it rises until it hits a plateau, but it bounces to the side of the plateau and it starts rising again. So there are two instances where the balloon starts to rise in this one animation. The problem was that the balloon sped up faster in one occasion than the other.
The thing that the animator should have paid more attention to is that the weight of the balloon and gravity will remain the same during the whole of the animation. So this means that the balloon should gain height and gain speed at the same rate in both occasions.
Of course exceptions can be imagined, like a fan below the balloon, but there was no fan in this particular animation, so it was a mistake.
Force / Energy
Energy, another consistent attribute in animation! No scientific explanation here, just a healthy dose of logic.
If you reach out and put your fist out reaaaaally slowly, you won't give someone a black eye now would you? Basically it's a matter of keeping track of the energy that is put into an action, and comes out. Those values should be (about) equal in your animations (again, exceptions aside).
EXAMPLE: It's bouncing ball time again! (part 2)
After a nice big bounce, the ball gathers downward momentum as it speeds towards the ground. Once the ball hits the ground that downward momentum is instantly converted to upward momentum. So the speed at which the ball was approaching the ground then becomes the exact speed at which the ball moves up and away from the ground. It steadily (, proportionally, consistently!) loses energy again due to gravity until it has no upward energy anymore and starts moving down with the energy of the gravitational force.
Also notice that when your bouncing ball moves sideways, it only slightly loses sideways momentum due to air resistance. After it stops bouncing it'll lose sideways momentum faster due to friction with the ground.
If the ball hits a wall, the sideways left momentum becomes sideways right momentum without losing any energy, it just gets changed in direction.
EXAMPLE: Hitting an invisible brick wall, or the likes
Bit of a tough one to explain, but a problem I've encountered in my own animations a couple of times. Let’s just take the arms in a walkcycle as an example. The arms swing back and forth during a walkcycle. They gain and lose momentum like a bouncing ball pretty much, except that most of the force comes from the muscles instead of from gravity. Sometimes it happens that the arms seem to hit an invisible wall in your animation. It feels like they should swing trough more, instead something invisible stops it from doing so. This means that the energy is cut short, the arm loses momentum unproportionally, too suddenly. It needs more follow through!
Related to this is the changing of amounts of energy in the middle of an animation.
EXAMPLE: The character jumps and after the apex of the jump, the return journey towards the ground is much faster than expected. It's like he's sucked towards the ground suddenly instead of it happening steadily.
EXAMPLE: Expectation of the viewer
If you see a big guy, like the Hulk, pull his arm back into a nice big preparatory swing, we as viewers start anticipating a big blow, right? Well let’s say he hits ye ordinary window with that big swing of his, but he doesn't manage to break the glass, well the glass better have some really good reason not to break! Now this is an exaggerated example of course, but it illustrates that the suspension of disbelief of the viewer can be broken by bad logic, so use this power well. Ask yourself if the result of the animation is what is logically to be expected.
A simpler EXAMPLE of this would be if the spring that is pushed down to half capacity, it won't spring up with the energy of a spring pushed down to full capacity.
Exceptions (full of EXAMPLES)
There are a lot of examples of exceptions to these little pieces of logic, but these examples are the result of specific choices made for the animation. Some examples:
Sometimes it's necessary to break gravity, for instance when blowing up an aunt (Harry Potter reference) or when your character is in a spaceship made by Bulma (DBZ reference). But that doesn't mean that animations aren’t consistent! They need to be consistent within their own context (very important!).
Another popular exception is the Warner Bros logic of hanging in the air before realizing there is no ground to walk on, then wave, and only then start falling. This is obviously a stylistic choice. But after starting the fall, the speed of the falling needs to be logical and believable.
EXAMPLE: Animation style
Another example where it's important to be consistent within the context of the animation is with stylistic decisions. The snappy timing in the below example isn't realistic, but it is consistent! What this means is that they've consciously adjusted the physical rules of their world, but the rules of gravity, weight and energy do still apply.
Well, the point is that we need to do everything we can not to break the suspension of disbelief of the viewer. It needs be believable. To consciously try and make it believable we pay heed to the rules of gravity, energy, weight, etc, etc. Even if the style of animation is different, or the situation you're animating isn't consistent with real life, it still needs to make sense, be consistent within their own context.
Yep! I think that's about it. I hope I included enough examples, haha.
I know the article isn't structurally coherent, sorry!
Any questions are more than welcome! Thanks for reading! J