# B Me, A Rod and A Table With Little Friction

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#### Erunanethiel

Lets say I have a massive rod laying on a table with little froction, screwed in to the table on one side to become our pivot point, and I lay next to it with my feet pointing towards the rod.

First scenario: I position myself very close to the pivot point and push, the rod rotates and I move across the table too.

Second scenario: I now position myself far from the pivot point and close to the free rotating side of the rod, and I push with my legs again with the same force and for the same duration of time.

Is there any difference in terms of how far I will go after I push and come to a stop where that little friction stops me between these two scenarios?

Is there any difference to how far will the rod rotate around the pivot point before that little friction stops it? (Assume I and the rod have have the exact same friction acting to both of us, so they cancel each other out)

Attempt at solution: I think I will move the same distance in both scenarios due to the impulse being the same, but I do not know about the rod, does me applying the same force for the exact same amount of time but at different distances from the pivot point affect how far the rod will rotate, I don't know

Thank you

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#### jbriggs444

Homework Helper
A fixed impulse and variable moment arm. Would you agree that it is a different impulse of angular momentum applied to the rod?

#### A.T.

... does me applying the same force for the exact same amount of time but at different distances from the pivot point affect how far the rod will rotate, I don't know...
Consider a distance of zero.

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#### Erunanethiel

A fixed impulse and variable moment arm. Would you agree that it is a different impulse of angular momentum applied to the rod?
So the rod will travel more in the second scenario?

#### jbriggs444

Homework Helper
So the rod will travel more in the second scenario?
Rather than directly answering that question, let me ask a different one.

Have you ever tried to open an un-latched door by pushing near the hinge?

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#### Erunanethiel

Rather than directly answering that question, let me ask a different one.

Have you ever tried to open an un-latched door by pushing near the hinge?
Yes it is harder to do so.

But if I push with the same force and for the same amount time near or far away from the hinge, I dont know if the amount of rotation the door changes, because even if the door is pushed close the hinge even though your hand moves very little with door, but the far end of the door moves quite a bit, sp I am confused.

#### jbriggs444

Homework Helper
Yes it is harder to do so.
To achieve the same motion, you must push harder or longer. Yes, I agree.
But if I push with the same force and for the same amount time near or far away from the hinge, I dont know if the amount of rotation the door changes,
Would you agree that the door moves more slowly if you push closer to the hinge? Does that not answer the original question?

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#### Erunanethiel

To achieve the same motion, you must push harder or longer. Yes, I agree.

Would you agree that the door moves more slowly if you push closer to the hinge? Does that not answer the original question?
So in the original question and in the first scenario when I am pushing close to the hinge with the same force and for the same amount of time, it makes the rod rotate less before it comes to a stop than in the second scenario where I am pushing far from the pivot point with the same force and the for the same amount of time correct?

#### jbriggs444

Homework Helper
So in the original question and in the first scenario when I am pushing close to the hinge with the same force and for the same amount of time, it makes the rod rotate less before it comes to a stop than in the second scenario where I am pushing far from the pivot point with the same force and the for the same amount of time correct?
Yes.

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#### Erunanethiel

Thank you

"Me, A Rod and A Table With Little Friction"

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