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billz9 · Oct 4, 2007, 10:26 AM

Hi there,

I'm in year 12 in england taking my advanced level in physics, however my understanding of moments is confused. I understand the clockwise turning moment needs to equal the anti-clockwise moment, however when I look at any question that involves 2 pivots or a change in the center of gravity I become confused as I don't know where to calculate the moment from.

Any enlightenment or example would be greatly appreciated!

Chris

ebaines · Oct 4, 2007, 02:30 PM

Perhaps you can post an example of the type of problem you're talking about. But in general: for a body in equilibrium the moments everywhere must be 0, which means you can often pick a convenient point to do the calculation. For example, if you have an unknown force it is often convenient to calculate the sum of the moments at the point where that force is acting, because that way the contribution to the moment by that unknown force is 0 (since the moment arm is 0). So by being clever with where you decide to sum up the moments you can often get to an answer pretty easily. Hope this helps.