Waiter minute
If I am serving a heavy rectangular tray of food, where should I hold the tray? Order them in ascending order of ease.
B = breadth (shorter edge), C = corner, L = length (longer edge), M = middle
Note: Assume the center of gravity is the geometric center. The rectangle is not square.
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1 solution
For all of them, you have to supply an upwards force; however, the torque you have to provide depends on the perpendicular distance from the pivot point - your hand - to the center of mass. (Torque is given by τ = r × F .)
Clearly, for the middle you have r = 0 , so no extra effort is needed. Now, here's the tricky part: if you hold it at the breadth, your r = L ; if you hold it at the length, your r = B ! So to hold it at the length is easier than at the breadth. Finally, of course, you would be insane if you chose to start with the corner easiest, since your r = L 2 + B 2 > L .