Physics Help Forum translational vs rotational equilibrium

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 Jan 21st 2014, 04:16 PM #1 Junior Member   Join Date: Jan 2014 Posts: 18 translational vs rotational equilibrium Is translational equilibrium is when the object has no net acceleration? (constant velocity or v=0) And rotational equilibrium is when an object has no net torque? Can an object be in translational equilibrium if it is not in rotational equilibrium? Thanks
Jan 21st 2014, 04:29 PM   #2
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 Originally Posted by FistLength Is translational equilibrium is when the object has no net acceleration? (constant velocity or v=0)
Yes (See - http://physics.bgsu.edu/~stoner/p201/equil2/tsld004.htm).

 Originally Posted by FistLength And rotational equilibrium is when an object has no net torque?
Yess. (See http://faculty.wwu.edu/vawter/Physic...uilibrium.html)

 Originally Posted by FistLength Can an object be in translational equilibrium if it is not in rotational equilibrium?
Think about this as follows - Can the net acceleration of a body be zero and the net torque be non-zero? Sure it can. If a momentum of a body is zero and remains zero and the torque is not zero then this situation holds.

Jan 21st 2014, 04:43 PM   #3
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 Originally Posted by Pmb Yes (See - http://physics.bgsu.edu/~stoner/p201/equil2/tsld004.htm). Yess. (See http://faculty.wwu.edu/vawter/Physic...uilibrium.html) Think about this as follows - Can the net acceleration of a body be zero and the net torque be non-zero? Sure it can. If a momentum of a body is zero and remains zero and the torque is not zero then this situation holds.
What confused me is the definition for translational equilibrium
Torque = force x length. If there is net torque, then net force is not 0, so we would agree that it is not in rotational equilibrium, but what is the definition for translational equilibrium (the website says an object not accelerating)? Because wouldn't the torque cause acceleration (centripetal?)

Sorry if there is a lot of mus-understaning in my post, I am pretty lay in physics.

Jan 21st 2014, 04:48 PM   #4
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 Originally Posted by FistLength What confused me is the definition for translational equilibrium Torque = force x length. If there is net torque, then net force is not 0, so we would agree that it is not in rotational equilibrium, but what is the definition for translational equilibrium (the website says an object not accelerating)?
That's not quite true. Remember that torque is a vector quantity. A force can be applied to one side at a distance r from the center of rotation while an equal and opposite force can be applied also at a distance r from the opposite side yielding a non-zero net torque by zero net force.

 Originally Posted by FistLength Sorry if there is a lot of mus-understaning in my post, I am pretty lay in physics.
No worries my friend. We've all been there. That's why this place is here. To answer just these kinds of questions.

Jan 21st 2014, 05:14 PM   #5
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 Originally Posted by Pmb That's not quite true. Remember that torque is a vector quantity. A force can be applied to one side at a distance r from the center of rotation while an equal and opposite force can be applied also at a distance r from the opposite side yielding a non-zero net torque by zero net force. No worries my friend. We've all been there. That's why this place is here. To answer just these kinds of questions.

Is this what you are talking about?
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Jan 21st 2014, 06:37 PM   #6
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 Originally Posted by FistLength Is this what you are talking about?
In your diagram there is the force of gravity acting along the centerline of the board counter balanced by the force of the support. That just complicates things.

Actually I had more along this in mind.
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Jan 21st 2014, 06:53 PM   #7
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 Originally Posted by Pmb In your diagram there is the force of gravity acting along the centerline of the board counter balanced by the force of the support. That just complicates things. Actually I had more along this in mind.
Oh ok yes I see what you mean. Thank you

Jan 21st 2014, 08:17 PM   #8
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 Originally Posted by FistLength Oh ok yes I see what you mean. Thank you
Excellant!

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### when is a body said to be in rotational equilibrium but not in translational equilibrium and vice versa

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