This post is about something that seems really logical if you think about it, but that can easily slip through your fingers when you animate. It's about how a body or object's weight and flexibility, and muscular tension too, affect its animation.
A heavy body will start slowly and take time to stop (and vice versa). A flexible body will allow limbs and spine to arch a lot and reach extreme positions. For example a well lubricated joint has minimum friction, if it also has nothing to stop it from spinning (no limits), when set in motion it'll keep on rotating for a long time, and when it settles, it does it gradually, and just as slow. Basically, it comes to a slow stop. In a world with no friction, it would just go on rotating forever. Don't mix flexibility with (muscular) tension though. A relaxed joint will move freely, and if also flexible, will move for a long time before coming to a stop. A rigid relaxed joint will also move freely, but will feel differently, and come to a much faster stop - because of friction. On the other hand, a flexible joint that has tension holding it, will not move freely. I think it's of... really paramount importance in animation to be aware of the degree of flexibility your character has per each articulation (OK, it's not like you're writing a table and have to animate mathematically to get this right, I just mean an animator should normally be generally aware, and the more aware, the better), and of the character's weight (also the weight and flexibility of the inanimate objects, the ones it comes in contact with for example), and of its muscular strength. A heavy, large, strong, and flexible mean killing machine is way scarier than a heavy, large, strong, and rigid one ;) And also, while animating, one should be aware of overall distribution of tension - sometimes you might need to keep certain parts more relaxed than others, and then a movement can start overall-relaxed and build more and more overall-tension on the way. So: weight is constant and has to remain constant (unless the character grabs a heavy object and increases its weight, so you animate the change of weight, but then you keep it constant again)!!! Muscular strength is also constant, you don't get stronger over night... oh, but you could fake you are weaker, or lose your strength because of whatever stuff that happened. When tired, body becomes weaker. But in normal conditions, muscular strength is constant. It doesn't normally increase or decrease in a short period of time such as within a shot :D Flexibility is again a constant, yeaaaaaaaaaaay!!! Constants rock, because they make our work harder... OK, I was being stupid. But they do rock actually, because we can decide on a character's constant values and therefore create a believable, constant performance. Yeah, the problem is obviously that it's hard to keep being aware of these constants. If you animate a loony cartoon you might not need to, you could be more flexible, but in most cases, if you need a believable, physically constant character... you need to be aware of your 'constants'. Tension is relative, so we have more freedom here, but... no, not really. Actually if I think more about it, maybe it's easier to handle constants. Because with tension you have to be aware not of ONE constant, but of the continuous process of tensioning and relaxing. You have more freedom though so people can't notice or feel imprecision like with messing up 'constants'. If you put more or less tension in a movement it's OK, if you don't put tension in a movement that requires tension, it's not OK. But if you change the amount of weight or flexibility of a body or object... without any obvious reason... that's easily noticeable.
Let's give some examples.
Heavy, rigid, tensed
Moves slowly because of rigidity. Puts a lot of effort because of weight and rigidity. Tension can add shuddering here and there, but also make the movement overall smoother - with tension you fight rigidity. So a lot of tension for example can make a little rigidity not even matter. But a lot of rigidity can make tension (if not enough) useless. This kind of character moves pretty even, not necessarily smooth (depending on the amount of tension), but even.
Heavy, rigid, relaxed
Barely moves at all if really rigid. Relaxation within a very rigid body equals no movement at all.
Heavy, flexible, tensed
This is a lethal combination :) Can inflict maximum damage (with added speed, weight increases, force becomes more destructive - I'll talk more about this some other time). It can start faster than expected, depending on the amount of tension, it's very smooth because of tension. Can also come to a smooth stop. It all depends on the balance weight/tension. With lots of weight and little tension, the body is out of control, and vice versa. The combination of flexibility and tension makes this character a very precise type.
Heavy, flexible, relaxed
Potentially lethal :) This type is just as precise, but we can see a major difference - the movement, even though elastic, comes to a fast stop - because of weight. This is a very "affected by gravity" type, all flows downwards.
Light, rigid, tensed
The slightest breeze can put it in motion and it can't really fight it, because of rigidity and lack of weight. The movement starts hard because of rigidity (a lot of force is not so believable for this type, especially because of lack of weight, but with a lot of tension, some of that rigidity can be defeated: again, same things apply here as in the first type, same balance of rigidity vs tension) but stops easy because of no weight to keep it in movement. A very rigid light body with a lot of tension in it might shudder a lot, more than in the case of a heavy body (not sure on this though, maybe it's only a matter of rigidity vs tension, and weight's got nothing to do with it).
Light, rigid, relaxed
Just as dead as the heavy counterpart. Basically, with a rigid body, you need noticeable tension to move anything. The weight is shown through interaction more than on its own.
Light, flexible, tensed
This is the ninja :D It's arguable which is more lethal, the heavy or the light type. Depends on the overall balance of elements. The light type can be faster, or at least faster to start. Dimensions also matter, of course - a small ninja would be insignificant to a huge flexible and fast beast. Now I'm talking extremes, you can figure out lots of unique middle ways. So - very fast to start and stop (because of lack of weight) and very precise (because of flexibility).
Light, flexible, relaxed
Same as with its heavy counterpart: potentially ninja. This is the type that flows the best, goes with the flow. If really light and blown away by the slightest breeze... it can easily float and flow with it, not against it. Lots of cartoon characters would fit in the 'light and flexible' family.
The follow through I mentioned in the title can apply to any of these types, and should be animated to fit that specific type - for example flexible relaxed hands will have a lot of follow through after a broad body action, but if the body and hands are both very heavy there will be little follow through, or at least with fast settle. The follow through can be measured in how extreme (broad vs subtle) it goes, how irregular it is (rigidity introduces irregularity in animation, because of friction, while flexibility will flow on rounder arcs) and how slow or fast it settles. Heavy objects imply faster settle, flexible and relaxed objects imply broader follow through. And vice versa.
All this stuff looks very arid and academical but in fact it's a simple matter of logic, of watching the world and taking into account gravity... friction... stuff like that. It's actually easier to learn visually, I put these ideas down on "paper" here, but if I animate, I don't really think mathematically about this, but logically. Before animating, I try to decide - OK, this guy weighs some 60 kilos, is an old guy but not so rigid, he's not as flexible as a 12 year old, of course, but not as rigid as most other people his age... he's got flexible wrists for example, but his spine is not as flexible, his feet are flexible, he jogs a lot, but his neck is rigid... And so I build an image of this character that I try to keep at the back of my mind as I animate. Actually it would be really fun to animate a character like this: rigid upper body but very flexible hips and legs and feet. Right? How about the other way around? Rigid lower body and flexible arms and spine and neck... and then you post it for crits and people will go "why those legs sure look awful, go back and fix em". Yeah, you should have a reason, normally, for doing such a thing... It can be done for fun, just because, but in a film... it has to have a logical reason.
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About me
I'm a character animator, visual artist, game dev, and music composer. I like to doodle, write, experiment, and plan my next big thing. I love tech that inspires and enables art. I have a formal background in music composition. And I like to walk around the world and see things up close. Archives
February 2022
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