How does a simple balance scale work?

  • #1
54
15
Visualize a simple balance, a pan at either end of a beam which balances on a fulcrum. The way it works is that if each pan carries the same weight, it balances horizontally. If one pan carries slightly more weight, it tips slightly off horizontal. If one pan carries more weight yet, it tips farther off horizontal. But that is not the way it would work if simple physics is applied to my simple model: for equal weights it would balance horizontal or not, and for unequal weights it would rotate fully until it came to a stop, regardless of how unequal they were. There must be some simple explanation, but I have not been able to find it.
 

Answers and Replies

  • #2
jbriggs444
Science Advisor
Homework Helper
9,937
4,532
The pivot point is slightly above the attachment points for the pans. As the beam tilts right, this means that the rotation moves the pans very slightly left. Similarly, if the beam tilts left, the rotation moves the pans very slightly right.
 
  • #3
2,167
499
The pivot point is slightly above the attachment points for the pans.

The weight of the index needle also results in a counter torque.
 
  • #4
54
15
Actually, I found the answer in an earlier thread. It is really quite simple. The center of gravity of the unladen scale is below the point of support (fulcrum) so when the scale tips, there is a restoring torque. I think this thread can be closed.
 

Related Threads on How does a simple balance scale work?

  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
12
Views
1K
  • Last Post
Replies
2
Views
4K
Replies
1
Views
1K
Replies
5
Views
3K
  • Last Post
Replies
6
Views
3K
Replies
5
Views
2K
  • Last Post
Replies
7
Views
4K
Replies
17
Views
7K
Top