Center of Gravity (COG) Definition--The Point located at an

object’s average position of the weight In other words…. The center of an

object’s weight Symmetrical object’s, like a baseball

the C of G would be in the exact center of object However other oddly shaped objects will

find COG in any number of positions, depending on weight distribution

COG

C.O.G. When objects rotate freely they must

rotate about an axis through the COG

Basically treat the object as if all its weight is concentrated at that one pt.

In class demos…

C.O.G. --Balancing For an object to balance,

and not topple… support must be directly below C.O.G.

Where C.O.G. is located Generally found in the

middle of all the weight… Does not even have to be

within, the object itself Ex. boomerang

Will be located toward one side of an object where most of its mass is focused… Ex. Weebles

COG

gravity

Weebles Wobble, but they don’t fall down??? Weebles have very low COG Whenever rolling it will roll to a

stop when its COG is as low as possible This occurs when it is standing upright Also occurs for inflatable toy clowns

Objects with a low COG are less likely to topple because of this principle

Higher COG is, the easier to topple

Balancing Stuff Again, all that has to happen to

balance, is for a support to be directly beneath COG

Advantages of low COG Athletic advantages

wrestling—harder to takedown

Football Both easier to drive power

through their legs SUV’s …. Tip over all the

time b/c COG is too high SUV Farmer’s tractors

Much more control in all vehicles w/ low COG

Animals

Low COG High COG Low COG High COG

Humans - Where is our COG? Just below our belly

button Notice, support

always below COG Bipedalism??

Only mammals w/ this ability to walk on 2 legs

Because of Evolution and how our legs changed to balance between steps is why we are only mammals to walk

Robots – Where is the COG?

Where is this robot’s Gravity “Average Mass” Centered?

A

B

C

Robots – Center of Gravity

Is this robot’s gravity more centered at it’s starting point “A,” or in it’s current position, “B?”

How do you know?

AB

Robots – Center of Gravity

How has the builder of this robot considered centering the gravity for the task that it has to accomplish?