Is Sandra Bullock in balance?
Wait.. Does she have two left hands? Ok that's not the question...
How can you be sure your character is in balance? Let's find out... And it all starts with the center of gravity...
Here is what we are covering:
What is the Center of gravity?
What is balance?
What is the base of support?
What about human characters?
COG fun facts.
1 - What is the Center Of Gravity (COG)?
It's two important things!
It is the point where your mass is concentrated
it is the center of rotation of an object (or Sandra Bullock)
2 -What is balance?
It is when an object or a character can stand still without falling.
The building is well balanced.
The building is not balanced, it falls.
What about this one?
Let's find out.
First, let's find the Center of gravity (COG) of this building. Its shape is simple, it's made of concrete only. Well the COG will be right in the center here:
3 - What is the Base of support
The base of support is the area of contact between an object and its support .
And now the golden rule: For an object to be balanced, the center of gravity must be over its base of support.
How does a base of support look like ?
In this case, it is quite simple. The base of support is this green square, which is the same shape as the building.
What about a fancy object like a tripod?
Individually, each pod has a base of surface like those red dots. But as one main object, the base of surface is this:
So, while the COG is over the base of support, the tripod won't fall.
4 - What about humans ?
Where is the human's Center of Gravity?
Men's COG is usually on the chest's center.
Women's COG will mostly be around the belly button. Why don't we have the same COG? Women's legs are usually longer than men's. Their hips also are generally larger while mens have larger chests.
Keep in ming each body is different, this is a general tendance, not a universal truth. Take time to observe your design and figure out the logical COG position.
This is why you can see all a fuzz around the "Center of gravity challenge" on youtube.
What is the base of support for humans?
You got it. While the COG is over the green base of support your character will be balanced.
5 - COG Fun Facts
The COG can be outside an object!
The COG is not alway in the center.
The COG can move
Indeed if the object change his shape, the COG will move accordingly.
Let's take the example of a character doing a backflip.
As the character is straight, the COG is situated in his chest.
When the character is packed with bend legs, the COG moves somewhere between legs and chest. You can see how the COG is the center of rotation. So if you have to animate a backflip with 3d animation, remember to animate your pivot point. By the way, did you notice how this COG act like a bouncing ball?.
Now you have a better understanding of the physics behind the center of gravity and balance; your next walk cycle will look better...
So, is Sandra Bullock in balance?
Not quite! Almost there Sandra, move a bit to your left... Bring your right foot in...
