I find that the forces acting on a pendulum bob are treated in two different (contradictory?) ways.(adsbygoogle = window.adsbygoogle || []).push({});

Let the angle that the cord makes with the vertical be x, the mass of the bob m and the tension in the cord T.

1. In one case, the weight of the bob is resolved into components so that mgcos(x) is along T, so T = mgcos(x).

2. In another case, the tension is resolved into ITS components, so that mg = Tcos(x).

Obviously only one of them can be correct at one time. I can't figure out which of them to use and when.

I am a physics teacher, by the way.

Thanks in advance.

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# Forces on pendulum

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