Rigid Bodies in Equilibrium in Physics

A body can sit still and still be about to tip over, which is why equilibrium needs two conditions rather than one. The first says the forces must cancel, so the body does not drift away. The second says the turning effects must cancel too, so it does not rotate. Only both together make something genuinely at rest, and a bridge that fails the second test while passing the first is exactly the kind of problem this topic exists to catch. The blocks give the two conditions, the torque relations that go into the second one, and the point at which the whole weight can be treated as acting.