Assume if we had a 2 tonne weight placed on ground attached with a rope that we can use to turn the object around. It will immensely hard to turn that object around by pulling the rope. However, if the weight was lifted to a certain height by a crane, when we try to turn that weight around; the force and the work is very low compared to the force needed to move the same object when it is on the floor.

Why is this?

Does the earth gravitational pull affect the amount of force required to turn the object?

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    $\begingroup$ Do You mean the lack of ground friction when the object is lifted? $\endgroup$ – Wojciech Mar 4 '14 at 21:44
  • $\begingroup$ @Wojciech You could say that. I don't see how the friction can make a real difference on the force needed to turn. I understand it contributes to the turning force to a certain extent. But, it doesn't contribute to all of the force. $\endgroup$ – Vaishnavi Mar 4 '14 at 21:51
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    $\begingroup$ Around which axis would You like to turn the object? $\endgroup$ – Wojciech Mar 4 '14 at 21:58
  • $\begingroup$ Assuming the weight is cylindrical, I would say somewhere in the middle of the side of the cylinder. $\endgroup$ – Vaishnavi Mar 4 '14 at 22:00
  • $\begingroup$ So the block will move in relation to the ground and the friction forces will act against. That is the only reason. $\endgroup$ – Wojciech Mar 4 '14 at 22:03

It is the elimination of friction on the ground. The friction on the air is very small, as is the resistance of the rope to twisting. No matter how smooth the floor, the friction will be much higher than the resistance of the hanging weight. This is why air bearings were invented.


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