(ELI5) What is the center of gravity?
In: 9
Cut an arbitrary shape out of thick card. Poke a hole in it near the edge and hang it from a piece of string through the hole. Draw a line vertically downwards from the hole to the other side of the shape. Now poke another hole elsewhere around the edge and repeat the process. After a few goes you should notice that all the lines you draw meet at one point. This is the centre of gravity of the shape.
The same idea applies to any 3D object; there will be some point which will always be under the suspension point. For an animal this is slightly complicated by the fact that they can change shape.
If you stick your arms out forward then you need to lean back slightly to keep your centre of gravity over your feet; otherwise you would fall over forwards.
Where the centre of gravity is will affect how stable something is, or where you should push the object to avoid tipping it over.
First off that’s isn’t biology.
But basically the center of gravity is like a magic spot on an object where all the weight is piled up. It’s a special spot that tells us where the object is heaviest. Sometimes the magic spot is in the middle of the object, but sometimes it’s not. We can find out where the magic spot is by hanging the object from two different places and seeing where it balances. Scientists have special books that tell them where the magic spot is for different shapes of objects. Does that make sense?
The center of gravity is essentially the same thing as the center of mass.
If you have some spherical object with the same density in it, the center of mass will be in the middle. But if say the left side is heavier than the right side, that center of mass will be more on the left side than the right.
When you are dealing with gravity all mass will pull slightly towards them, but doing all these calculations is impossible. So what you do instead of calculate the center of mass, and you can mathematically prove that the calculations for gravity end up the same if ALL the mass was just located at the center of mass, instead of being spread all over the place.
Centre of gravity and centre of mass are essentially equivalent in most practical circumstances.
Centre of mass is an an imaginary point where an objects’s inertia acts. The position is determined by the location and density of all of the object’s connected masses. Applying a force to the object’s centre of mass moves it without inducing rotation.
Centre of gravity is an imaginary point through which the collective gravitational force of an object’s mass acts. Here on earth, the top of an object experiences less gravitational force than the bottom, meaning it’s centre of gravity is below its centre of mass.
The distinction is meaningless for small objects here on Earth. However, large objects space will rotate if their centre of mass and centre of gravity do not align along the axis of gravitational force acting through the centre of gravity.
The center of gravity is just the average location of all of a thing’s weight.
Gravity acts on mass. Every piece of an object has mass and is pulled on by gravity (producing weight).
Figuring out how gravity affects something with a complicated shape can be tough. One trick is to imagine the object is actually just a single point with the same total mass.
Of course, you want this point to be located where the average of all of the object’s mass is – and that’s the center of gravity.
So for example, if you want to figure out whether someone is going to fall over or not, you can just check whether their center of gravity is over a part of their feet. If it’s not, they’re going to fall.
It’s effectively a summary of where gravity is applying force to an object.
Gravity has a effect on all parts of an object. But it is quite hard to consider all parts so it is a good idea to try to simplify things.
Take a broom and try to balance it horizontally on a finger. Your finger can’t be in the middle of it. the broomstick is lighter than the Broomhead so you need to be close to the broom head. So when you find the point it can balance of you finger you find the point where the center of gravity is that is also the center of mass.
That point is more exactly a vertical plane going you the center of gravity. You can rotate the broom horizontally 90 degrees to find it for that configuration too and then 90 degrees vertically. So when you have done that for all directions you have the center of gravity.
So the center of gravity is the point it could balance at regardless of how you point it. How you in practice could attach it is another completely different problem.
In biology, you have a system of humans that are not solid like a broom but can change the configuration so the center of gravity change when you move around.
If you center of mass is outside what supports it below and you are just starting on something you will start to fall over at that point. Look at calculator-online.net/images/Fig20_Principle1-min.jpg and in the case of C you would start to fall over. You would need to have the foot attached to the ground to still be able to stand like that. Screw a shoe to the floor and then keep your feet in it by tying the shoe laces and could still stand. The shoes need to be strong enough and not break too.
You can and do exploit this, by walking and primary running are you moving so the center of mass is outside the support and you start falling in that direction, you are just moving the other leg forward to stop you from hitting the ground.
It’s a theoretical point where you can consider the mass of the object to be.
When calculating the outcome of physics or mechanical problems, it’s way simpler to assume all the mass to be in one point and calculate the outcome for that.
But you have to calculate in advance where exactly this point is or it doesn’t work.
For simple object it’s quite easy to find, in a sphere or a ball, the center of mass is in the geometrical center of the object. On a truck? Well you need to do a lot of math. It may take less to actually weigh the truck from each wheel and calculate the center of mass using this empirical data.
But once you have that center location, you can calculate things assuming all the truck’s mass is in that point. You can calculate that complex object’s behavior with ease. How much that truck will lean forward when braking, how balanced will be in a turn… easy stuff to do once you know its mass and where that mass virtually is.
It doesn’t apply to all problems, there are things you can’t calculate by using the center of mass as a substitute for the real mass. For example the rotational momentum of an object can’t be calculated with this method.
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