Why Does a Balance Regain its Equilibrium Position?

  • Thread starter ashishsinghal
  • Start date
  • Tags
    Balance
In summary, Abdul Quadeer and Phrak say that a balance with a pivot below the center of the beam will not regain its original position, while tiny-tim and Jarednjames say it will.
  • #1
ashishsinghal
462
0
If an ordinary balance with two equal weights is displaced slightly from its equilibrium position then it regains its original position. Why?

There is no unbalanced torque at any position. So why should it regain its position? I am totally confused on this one. Can anyone help...
 
Physics news on Phys.org
  • #2
hi ashishsinghal! :smile:

if you're talking about a see-saw balance with the pivot in the centre of the beam, then you're correct …

the beam will stay in whatever position you put it

but if the pivot is above (or below) the centre of the beam, there will be a torque, and it will return to the level position :wink:
 
  • #3
I thought of the same thing but if the weights are tied to the see-saw balance with a string, then ? because that is an ordinary balance
 

Attachments

  • 2dRS3kW.jpg
    2dRS3kW.jpg
    4.3 KB · Views: 370
  • #4
To restate tiny-tim:

If the pivot is in the centre of the beam, no matter where you position it, it will remain where you leave it.

If the pivot is above or below the centre of the beam, it will return to somewhere around the equilibrium position.

Do you understand this point?

What do you mean tied with a string? As in you tie them to each end of the beam with string? Because that isn't an ordinary balance. You usually have two pans that masses can be put into.
 
  • #5
I understood that point. Maybe the term "ordinary balance" confused me.
Thanks
 
  • #6
ashishsinghal said:
I thought of the same thing but if the weights are tied to the see-saw balance with a string, then ? because that is an ordinary balance

it makes no difference …

each weight will still be vertically under the point that its string is attached to …

the torque is exactly the same as if the weight was at that point :wink:
 
  • #7
yeah, that is what my point was, here the center of mass of beam is below the pivot point but it will still not regain its position.
 
  • #8
There is usually a small mass attached to the pivot in the case of an ordinary balance. This provides the restoring torque. Refer the figure:

[PLAIN]http://img11.imageshack.us/img11/9684/baler.jpg [Broken]

Notice that the centre of mass of the attached mass is below the pivot.
There might be other constructions too but this is what I am familiar with.
Hope that helps :smile:
 
Last edited by a moderator:
  • #9
That attached mass is generally a needle pointer and would not have adequate mass for restoring.
 
  • #10
ashishsinghal, in a balance the pans hang over pivots, the central pivot is raised slightly above the centerline between the two hang points. The metrology laboritory where I work has one on display. A beautiful work of art, circa 1950 I suppose, made of brass, glass enclosed, and full of knobs to remotely move around weights from outside the enclosure. The enclosure prevents air currents from disturbing the reading. I can't find an image online that is remotely equivalent.

Abdul Quadeer is correct. A center of mass of the beam, below the center pivot would have a restoring force, but one that is constant rather than proportional to the load. I would guess you'd want the restoring force proportional the the load, as the pivot friction should be proportional to the load, as well.
 
Last edited:
  • #11
Thanks, now I know the reason for both the kinds of balances - one by Phrak and Abdul Quadeer and the other by tiny-tim and jarednjames. Thanks to all of you.
 

1. Why does a balance regain its equilibrium position?

A balance regains its equilibrium position due to the law of conservation of energy. When a balance is disturbed and moves away from its equilibrium position, it gains potential energy. This energy is then converted back into kinetic energy as the balance oscillates back and forth, eventually coming to rest at its equilibrium position.

2. What factors affect the time it takes for a balance to regain its equilibrium position?

The time it takes for a balance to regain its equilibrium position can be affected by several factors, including the mass of the balance, the distance it is displaced from its equilibrium position, and the strength of the restoring force.

3. Can a balance ever achieve perfect equilibrium?

In theory, a balance can achieve perfect equilibrium if all external forces are eliminated and the balance is in a vacuum. However, in reality, there will always be some external factors (such as air resistance) that will prevent a balance from achieving perfect equilibrium.

4. How does the length of the balance arm affect its equilibrium position?

The length of the balance arm affects its equilibrium position by changing the moment of inertia of the system. A longer balance arm will have a greater moment of inertia, making it more difficult for the balance to return to its equilibrium position.

5. What role does gravity play in a balance regaining its equilibrium position?

Gravity plays a crucial role in a balance regaining its equilibrium position. The pull of gravity is what creates the restoring force that brings the balance back to its equilibrium position after it has been disturbed. Without gravity, a balance would not be able to return to its equilibrium position.

Similar threads

  • Classical Physics
Replies
4
Views
533
  • Classical Physics
Replies
18
Views
564
Replies
9
Views
2K
Replies
3
Views
2K
Replies
12
Views
1K
Replies
8
Views
763
Replies
6
Views
671
  • Classical Physics
Replies
10
Views
852
  • Introductory Physics Homework Help
Replies
14
Views
602
Replies
5
Views
517
Back
Top