Force — Important Questions

Frictional force, Normal reaction force, Tension in a string

Contact forces require physical contact between objects. Friction, normal reaction, and tension are contact forces. Gravitational and magnetic forces are non-contact forces that act at a distance.

Newton-metre (N-m)

The SI unit of moment of force is Newton-metre (N-m), which is the product of force (N) and distance (m).

Magnitude of applied force, Distance from axis of rotation, Sense of rotation (clockwise or anticlockwise)

Moment of force depends on the magnitude of force, the perpendicular distance from the axis, and the sense of rotation. Mass and temperature don't directly affect the moment.

Two equal and antiparallel forces acting at different points

A couple consists of two equal forces acting in opposite directions (antiparallel) at different points on a body, producing pure rotational motion.