Define torque, and state the conditions necessary for stable equilibrium.

Torque, also known as moment or moment of force, is a measure of the force that can cause an object to rotate about an axis. It is a vector quantity, meaning it has both direction and magnitude. Torque is calculated by multiplying the force applied by the distance from the axis of rotation to the point where the force is applied.

Mathematically, Torque (τ) = Force (F) x Distance (r)

The conditions necessary for stable equilibrium are:

1. The net external force acting on the body must be zero. This means the sum of all forces acting on the body should be zero, resulting in no linear acceleration.

2. The net external torque acting on the body must also be zero. This means the sum of all torques acting on the body about any axis should be zero, resulting in no angular acceleration.

3. The center of gravity of the body must be directly above the base of support. This ensures that the body does not start to rotate.

In summary, for a body to be in stable equilibrium, it must be at rest or moving with a constant velocity, and it must not be rotating or have any tendency to rotate.