<p>I know that usually, it’s</p>
<p>F = -dU/dx
and similarily
τ = -dU/dθ</p>
<p>But a lot of times, I’ve seen the negative sign ignored (e.g. [Torque</a> - Wikipedia, the free encyclopedia](<a href=“http://en.wikipedia.org/wiki/Torque]Torque”>Torque - Wikipedia) and my physics textbook a lot of times when deriving equations), and I was just wondering why.</p>
<p>I’m not sure… my level is only SAT 2 physics… But usually + and - represents the opposite…
So if its - , i’m assuming it is torque’s direction is the other way? Since the unit for torque is newton meter… Force could be push or pull, tbh man I don’t really know :P</p>
<p>take gravity as an example. The force acts down, but U increases as you move up, so dU/dx would be positive, so you need the negative sign</p>
<p>sometimes, they just ask you for the magnitude of the force or torque, so the sign doesnt matter</p>
<p>Never mind, it was one of those unbounded types of potential energy, like when you’re really close to the surface of an electric field or like what ca4444 said.</p>
<p>The derivatives you posted apply for conservative / restoring forces.</p>
<p>For example, in ideal situations the bob of a pendulum swings forever. The horizontal component of gravity provides the torque that allows the pendulum to swing in place.</p>