why is the gear ration 2 : 3?

Question

Why is that the most efficient transfer of energy is done when the 2 : 3

http://www.theblattners.com/hobby/Broken%20Spur%20Gear.jpg

And the smaller one is 2 and longer one is 3.

This also makes me to ask this question. Why is it that when we move away from fulkrum on a sea-saw, we actually bend it more towards ourselves, even though we are away from the point on which we are going to put force.


Thanks in advance

NeuroProf · Accepted Answer

It means that for each 2 turns on one gear, there are 3 turns on the other (though I assume you know that already).  The efficiency is related to friction loss-the greater the ratio difference, the greater the force transer and thus friction loss, so the lowest ratio difference is the one with the least friction loss.
There is no change in distance from the fulcrum on a see-saw unless you are talking about the very small bending of the board, and that is likely too little to overcome other small forces, such as friction, movement of the people on the seat, etc.

Ra.Ge · Answer

umm try to submit the two questions as seperate questions. thanks.

the first question does not make much sense. the efficiency of energy transfer does not depend upon the gear ratio. like the other person mentioned, it depends on frictional losses. It simply is not correct that the most efficient transfer takes place at the ratio 2:3

2. rotational forces are quantified as torque: which is the force multiplied by the perpedicular distance beween the point of application of force and the fulcrum. as you move away from the fulcrum distance increases and for the same force, the torque is higher
(for the same stationary force, the moments are greater)

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why is the gear ration 2 : 3?

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