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Character animation is basically bringing something to life using motion. Now, what creates motion? Well, as we've seen, forces are what create motion. Anything that's put into motion is subject to a force in one way or the other. Now there are two basic types of forces that can act upon a character: internal and external forces. Now, external forces are those that are from outside the character or from the environment. That will be stuff like gravity, wind, or any sort of mechanical force such as an anvil dropping on your character's head.
Now, internal forces are those that come from within the character himself and those are forces that are created by the muscles of your character and driven by the intelligence of your character. So the internal forces are really what bring your character to life. Now, when animating a character and trying to get a realistic animation, you need to balance both. You need to balance the internal forces of the character's muscles versus the external forces of the environment.
So let me show you how this works. Here we have a simple character and any character who is standing on the ground is subject to the force of gravity. So here we have a force, an external force, acting upon the character to pull him down towards the ground. Now, if the only force that was acting upon this character was gravity, the character would just sink into the ground. But the character does have muscles and his own internal forces or internal energy that he can use to counteract the force of gravity.
So when his legs light up or the muscles in his legs activate, he pushes against gravity and creates a counteracting or opposing force to gravity. And those two forces, the external force of gravity versus the internal force of the character, create a balance and so the character stands up. And if the character is just standing, those forces will continue to balance. But as soon as the character moves, changes his weight or changes that situation in any way, then the forces will become out of balance and the character will move.
So let me show you an example. Here we have a character who is just basically shifting his weight. He is going from his right foot to his left foot and that's it. Now, this really doesn't look all that realistic because we are not factoring in the external force of gravity. All we are doing is using the internal force of his legs. We're really not understanding how gravity is affecting this character's body. So when he animates, it just goes from one position to the other and it really doesn't have a sense of weight.
Because what's causing weight? Gravity. So what we can do is we can actually animate this character, so that it looks like there is gravity acting upon him. So first thing I am actually going to do when I animate this is I am actually going to turn off the legs, because I really just want to get the mass of the body moving. So right now, the mass of the body pretty much just moves in a straight line from frame 0 to frame 16, and I need to get a little bit more weight.
So what we can do is we can add in the external force of gravity. So as he moves, he is going to be shifting his weight from one foot to the other and in between those, there will be an imbalance of force and gravity will pull him down. So what I can do is just take his hips and drop them as he moves. So now, he is going to go down and then back up into his pose. But one of the things is that again his body is going to want to continue to move in the direction that it's going, again Newton's laws of motion.
So he is going to overshoot this final position a little bit. So instead of going right to the position, I'm actually going to go little bit higher and then settle him down. So now this gives a much better sense of weight. In fact, I've already animated this and I have put in the legs. So let's just go ahead and see how this looks. As you can see, it has a much better sense of weight just by adding in those external forces of gravity.
So when you animate your character, you need to balance the internal forces of the character's muscles and intelligence against the external forces of the environment in order to create a realistic animation.
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