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srijit
 3 years ago
when a body is weighed on an ordinary balance we demand that the arm should be horizontal if the weights on two pans are equal.suppose 2 equal weights are placed on either side, the arm is kept at an angle with the horizontal and released. is the torque of the 2 weights about the middle point(point of support) 0 ? is the net torque 0 ? if so why does the arm rotate and finally become horizontal?
srijit
 3 years ago
when a body is weighed on an ordinary balance we demand that the arm should be horizontal if the weights on two pans are equal.suppose 2 equal weights are placed on either side, the arm is kept at an angle with the horizontal and released. is the torque of the 2 weights about the middle point(point of support) 0 ? is the net torque 0 ? if so why does the arm rotate and finally become horizontal?

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MrDoe
 3 years ago
Best ResponseYou've already chosen the best response.0\[\tau=rF \sin \theta \] so plug it in, what does that tell you?

MrDoe
 3 years ago
Best ResponseYou've already chosen the best response.0r is the displacement vector btw

srijit
 3 years ago
Best ResponseYou've already chosen the best response.0dw:1357340856320:dw both the displaements appear to be the same

srijit
 3 years ago
Best ResponseYou've already chosen the best response.0as also they have the same force Mg acting on each of them one in clokwise and another in anticlockwise..so they cancel out and the net resultant torque is 0 about the centre

srijit
 3 years ago
Best ResponseYou've already chosen the best response.0so why does the body move then again?

srijit
 3 years ago
Best ResponseYou've already chosen the best response.0but the moment arm is that what matters right ? that is the perpendicular distance between the force and the axis of rotation..

srijit
 3 years ago
Best ResponseYou've already chosen the best response.0but torque is just MOMENT ARM * force right so why would the angle theeta matter..??

vf321
 3 years ago
Best ResponseYou've already chosen the best response.1Even if you just use the moment arm simplification, keeping track of your signs will still result in a consistent answer.

srijit
 3 years ago
Best ResponseYou've already chosen the best response.0@vf321 is this 0 in here?

vf321
 3 years ago
Best ResponseYou've already chosen the best response.1Yes, it is. In fact, if the weights are equal, the balance is ideal, etc., then the system will be static, just like an Atwood's machine where one of the weights is raised:dw:1357342611368:dw

vf321
 3 years ago
Best ResponseYou've already chosen the best response.1So long as the weights are equal, nothing will move.

srijit
 3 years ago
Best ResponseYou've already chosen the best response.0but in case of an atwood machine if one block is raised a bit above another and released then at that instant net torque is 0 still the block raised at a height comes down until both the blocks are at the same height right? why does it happen ?

vf321
 3 years ago
Best ResponseYou've already chosen the best response.1No, the blocks will not move. Why would they?

vf321
 3 years ago
Best ResponseYou've already chosen the best response.1(equal mass assumption, of course)

vf321
 3 years ago
Best ResponseYou've already chosen the best response.1Yes, if you were to plug in the values for the two torques, they would equal zero. If the system was not in motion initially, it cannot suddenly start moving w/o violation of energy conservation

srijit
 3 years ago
Best ResponseYou've already chosen the best response.0@vf321 but it does from observation..

vf321
 3 years ago
Best ResponseYou've already chosen the best response.1Of course! The reason we're not getting anywhere is b/c the problem is not welldefined.

vf321
 3 years ago
Best ResponseYou've already chosen the best response.1It depends on where your center of mass is. If your COM is perfectly in the middle of your axis of rotation, then what I described will happen.

rajathsbhat
 3 years ago
Best ResponseYou've already chosen the best response.0@vf321 is absolutely right! It has no reason to move. Try it out if you want.

srijit
 3 years ago
Best ResponseYou've already chosen the best response.0but how can they remain tilted in there with 2 equal masses on either side ? 2 equal masses always stay on the same level..

rajathsbhat
 3 years ago
Best ResponseYou've already chosen the best response.0that's the beauty of it. No torque=no movement unless it's already moving. You should really experiment with this the next time you get your hands on a balance.

VincentLyon.Fr
 3 years ago
Best ResponseYou've already chosen the best response.0Probably because of the weight of the arm itself. Its centre of mass G is always below the fulcrum A, either by position of the fulcum such as: dw:1357422838501:dw. or by shape of the arm, such as: dw:1357422965061:dw
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