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A level physics: Centre of mass question

My textbook says “for a uniform regular solids the centre of mass is at the centre of the object”. Below that text it shows 3 images, a ball evidently uniform regular, but then an asymmetrical and a certain metal object (I forgot what it’s called. Was the textbook intending to also show the car and the metal object are uniform regular?

I’ll put an image below
Reply 1
E1A488C7-5C4E-4CB2-8E81-123C3CB0AFC0.jpeg
Original post by Sha.xo527
My textbook says “for a uniform regular solids the centre of mass is at the centre of the object”. Below that text it shows 3 images, a ball evidently uniform regular, but then an asymmetrical and a certain metal object (I forgot what it’s called. Was the textbook intending to also show the car and the metal object are uniform regular?

I’ll put an image below

I don't think the book is saying the car is uniform. It is a little confusing - at least from the little bit I can see.
The sphere is uniform.
Uniform shaped solids would be things like a sphere, a circular object, a square, a rectangle.
The C of M with a uniform object like those is then where you would expect.
Uniform also means that the object has uniform density. That is certainly not the case for the car.
It does though, beg the question of where the 'centre of an object' is.
For example, the C of M of a ring or hoop is at the centre of the circle. So it isn't within a physical part of the object.
You see this with that horse shoe in the 3rd object.
The centre of mass of a triangle is, well, at the centre of the triangle. But where is that?
This can actually be determined by a bit of geometry.
yes uniform means uniform density in this context. A car, as mentioned, does not have uniform density but maybe close enough so that you can assume it does
Reply 4
Original post by Stonebridge
I don't think the book is saying the car is uniform. It is a little confusing - at least from the little bit I can see.
The sphere is uniform.
Uniform shaped solids would be things like a sphere, a circular object, a square, a rectangle.
The C of M with a uniform object like those is then where you would expect.
Uniform also means that the object has uniform density. That is certainly not the case for the car.
It does though, beg the question of where the 'centre of an object' is.
For example, the C of M of a ring or hoop is at the centre of the circle. So it isn't within a physical part of the object.
You see this with that horse shoe in the 3rd object.
The centre of mass of a triangle is, well, at the centre of the triangle. But where is that?
This can actually be determined by a bit of geometry.

I see, thank you for your reply, is the horse shoe uniform regular?
Original post by Sha.xo527
I see, thank you for your reply, is the horse shoe uniform regular?

The horse shoe is symmetrical. This means the C of G will be somewhere on the line of symmetry. As you see in the diagram.
But exactly where on that line is not so easy.
As you see, it isn't half way up the horse shoe, but nearer the bottom. (The closed curved end not the open end.)

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