View Poll Results: The center of force is same as the center of mass
Yes 0 0%
No 0 0%
Depends (show us on what) 4 100.00%
Voters: 4. You may not vote on this poll

Register to reply

The center of Mass perfectly match the center of Force->

by deda
Tags: force>, mass, match, perfectly
Share this thread:
deda
#1
Jan23-04, 09:14 AM
P: 184
In a system of several masses the center of force has same position with the center of mass in the geometrical space;

Yes or No?

Please explain why!!
Phys.Org News Partner Physics news on Phys.org
Researchers demonstrate ultra low-field nuclear magnetic resonance using Earth's magnetic field
Bubbling down: Discovery suggests surprising uses for common bubbles
New non-metallic metamaterial enables team to 'compress' and contain light
KLscilevothma
#2
Jan23-04, 11:46 AM
P: 321
I think the answer is no.

In my physics notes, it says, "If a body is placed in a uniform field of gravity then its centre of gracity will concide with the centre of mass. However, this may not be true for a very large object."

Well, I don't know what is one of the examples of "a very large object".
deda
#3
Jan23-04, 01:29 PM
P: 184
Originally posted by KLscilevothma
I think the answer is no.

In my physics notes, it says, "If a body is placed in a uniform field of gravity then its centre of gracity will concide with the centre of mass. However, this may not be true for a very large object."

Well, I don't know what is one of the examples of "a very large object".
Does your notes contain equations to support that?

kishtik
#4
Jan23-04, 02:20 PM
P: 115
The center of Mass perfectly match the center of Force->

I think some logic can be useful.
Think an object which you can hold. Keep it steady and release it. You'll see that it does't turn around(neglecting air friction).
But think a very large spacecraft(its length is two times the diameter of the earth) falling(!) to the Earth. A much greater force is exerted to the side which is nearer the earth, so it starts to turn. Obviously CM doesn't match FM.
Am I wrong?

But did you mean where there is no gravitational force between the masses by "center of force"?
ophecleide
#5
Jan23-04, 02:41 PM
P: 34
I think you are right, kishtik. The question is just too vague. Are we talking about a situation in which there is a uniform gravitational field and there are no other forces acting on an object?
Arcon
#6
Jan23-04, 08:15 PM
P: n/a
Originally posted by deda
In a system of several masses the center of force has same position with the center of mass in the geometrical space;

Yes or No?

Please explain why!!
Please defined center of force
deda
#7
Jan24-04, 07:57 AM
P: 184
Originally posted by Arcon
Please defined center of force
Actually, that was something that I wanned to request from some of you. Now that I'm being ask for it I'll say:

We have a system of several masses in empty space.
There is force field in every point of space.
The force center will then be exactly that point which contains the sum of all forces each mass is subjected to.
But don't count one force twice as Newton's III sugests while summing the forces.This requires that you relate geometry with force.
My only answer will then be based on summing energies.

[tex]\sum E_i = E_{cf}[/tex]

Since for me [tex]E_i=F_iD_i[/tex] where D is the distance and F is force in D from CF then

[tex]\sum F_iD_i=F_{cf}D_{cf}[/tex]

also

[tex]\sum F_i=F_{cf}[/tex] and [tex]\sum D_i=D_{cf}[/tex]
=> [tex]\sum_{i<>j} F_iD_j=0[/tex]
is the condition for balance in the system.

Now, be soft with your critics. I'm breaking the ice here.
kishtik
#8
Jan25-04, 06:41 AM
P: 115
Originally posted by deda
Now, be soft with your critics. I'm breaking the ice here.
I'm not a native speaker of English. I only tried to say that I did't know deeply what KLscilevothma's notes were about and I would do some guessing and mental experiments etc. I am shocked as I realised what "Some logic can be useful." meant. They do not teach things like this at school or course. I'm sorry.
davilla
#9
Jan25-04, 08:52 AM
P: 88
Okay, here goes a more "mathematical-style" proof of a physics problem I can't honestly claim I understand.

Suppose center of force = center of mass. Then take a system of such objects where this is true, and for which there is a single (nonzero) center of force.

Add an object which has no force applied to it that is not centered on the center of mass of the system. Then the collective new system has a different center of mass, but the same center of force. So the center of force and the center of mass are not the same.

Quel Est Des-probleme?
russ_watters
#10
Jan25-04, 10:43 AM
Mentor
P: 22,281
Not enough information given: you can apply a force whereever you want it.

If you're talking about gravity though, the answer is no.


Register to reply

Related Discussions
Center of gravity (it's not center of mass ) General Physics 28
The geometric center of the Earth and the center of mass Classical Physics 9
Can two objects with the same center of mass oscillate about that center? Introductory Physics Homework 0
Average force and center of mass Introductory Physics Homework 9
Help with problem of Center of mass, linear mass density and total mass Introductory Physics Homework 1