physics question centre of mass

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#1
In my CGP book it says that an object will always balance around the centre of mass point, but for some objects, the COM lies outside the object, so what happens here? does that mean the object can never balance?
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#2
In my CGP book it says that an object will always balance around the centre of mass point, but for some objects, the COM lies outside the object, so what happens here? does that mean the object can never balance?
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1 year ago
#3
clearly if there is nothing there then you cannot support the object at the COM.
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#4
(Original post by the bear)
clearly if there is nothing there then you cannot support the object at the COM.
So the object can never balance at a single point?
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1 year ago
#5
(Original post by vix.xvi)
So the object can never balance at a single point?
no. a simple example is a washer or a doughnut. the COM is in thin air.
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#6
(Original post by the bear)
no. a simple example is a washer or a doughnut. the COM is in thin air.
I see. Thank you!!!
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1 year ago
#7
(Original post by vix.xvi)
I see. Thank you!!!
i guess you could balance a doughnut on its edge, but the contact point would not be the COM.
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#8
(Original post by the bear)
i guess you could balance a doughnut on its edge, but the contact point would not be the COM.
Ooh whatt sorry how would that work then?
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1 year ago
#9
(Original post by vix.xvi)
Ooh whatt sorry how would that work then?
like this:

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#10
I see...

So it's centre is mass is acting through the base in that case right?
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1 year ago
#11
(Original post by vix.xvi)
I see...

So it's centre is mass is acting through the base in that case right?
the contact force is passing through the centre of mass, but that is not the same as "balanced at the COM point"
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1 year ago
#12
The centre of mass is what happens if you find an average position of all masses of all particles in the object, so for a donut then the centre of mass is in the hole in the middle. For physics at your level it is a good enough approximation when it comes to equilibrium. But these objects can balance
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1 year ago
#13
(Original post by vix.xvi)
In my CGP book it says that an object will always balance around the centre of mass point, but for some objects, the COM lies outside the object, so what happens here? does that mean the object can never balance?
No, it just means that the COM is keeping your balance, essentially. It doesn't necessarily always mean that the COM is something physical which you can hold to balance yourself. So for example, if there is a high jump runner, and they use their back to jump over the rod (overused example, I know), then at some point, their COM is outside their body. So the COM is keeping in check their balance. If the body turns more than a certain angle, perpendicular, for example, to the COM, the runner will fall. However the runner cannot exactly hold his COM to keep himself in check.
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