EK Physics 732

[IlyaR]

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Just wanted some clarification as I don't remember seeing any explanation for this in the EK review book.

Does torque always point in the direction of tension? I was under the impression that torque was pointing in the same direction as the applied force (basically I thought the direction of torque of a door was at the handle)

Also, the centripetal force is added to the mgCosTheta because tension>mg, right?

Thanks!

 

[monkeyvokes]

Just wanted some clarification as I don't remember seeing any explanation for this in the EK review book.

Does torque always point in the direction of tension? I was under the impression that torque was pointing in the same direction as the applied force (basically I thought the direction of torque of a door was at the handle)

Also, the centripetal force is added to the mgCosTheta because tension>mg, right?

Thanks!

yeah the tension is slightly greater than mg because the mass is accelerating.


The question doesn't mention torque. I don't know if I've seen a pendulum problem discussed in terms in toque, is it possible that they are just using that symbol for tension?

 

[September24]

Yeah, the t must be torque. The question doesn't seem to make sense.

Can you explain why tension must be higher than mg if it is accelerating?

 

[monkeyvokes]

Yeah, the t must be torque. The question doesn't seem to make sense.

Can you explain why tension must be higher than mg if it is accelerating?

the two opposing forces are tension and force due to gravity, mg. mg pulls the mass down and tension holds it up. The mass isn't accelerating toward the earth at that angle, so the force of tension must be stronger.
Here is a nice image:

 

[monkeyvokes]

That image also shows the tension (acceleration) being the greatest when the angle is zero

 

[IlyaR]

The question doesn't mention torque. I don't know if I've seen a pendulum problem discussed in terms in toque, is it possible that they are just using that symbol for tension?

Am I crazy or isn't the symbol in the question torque?

 

[monkeyvokes]

Am I crazy or isn't the symbol in the question torque?

Yeah that symbol is used for torque.
Googled pendulum torque, found this: http://hyperphysics.phy-astr.gsu.edu/hbase/pendp.html

I hadn't seen this before, but i suppose it makes sense that the length of rope is analogous to a lever arm and the mass is supplying a torque..

good ol physics..