Forces, Torque and Force Systems

A force is a push or pull that can change the motion or shape of an object. Forces are vector quantities, meaning they have both magnitude and direction, and when several act on a body they combine into a single net force. When that net force is zero the object is in equilibrium, remaining at rest or moving at constant velocity. Analysing the system of forces acting on a structure or machine is a core task in mechanics and engineering.

Torque, or moment, is the rotational equivalent of force. It measures the tendency of a force to turn an object about a pivot and depends on both the force and its perpendicular distance from the axis of rotation. A larger lever arm produces more torque for the same force, which is why door handles are placed far from the hinges. For a body to be in complete equilibrium, both the net force and the net torque must be zero.

Newton's third law states that forces always occur in pairs: when one object pushes on another, the second pushes back with equal magnitude in the opposite direction. The Coriolis effect is an apparent deflection of moving objects when observed from a rotating reference frame such as the Earth. It curves the paths of winds and ocean currents, turning them clockwise in the Northern Hemisphere and counterclockwise in the Southern, and it is important in meteorology and large-scale fluid motion.

Frequently asked questions

What is the difference between force and torque?

Force tends to cause linear motion, while torque tends to cause rotation about an axis. Torque depends on the force and its distance from the pivot point.

What does Newton's third law say?

It says that every force comes in a pair: when one body exerts a force on another, the second exerts an equal and opposite force on the first.

What causes the Coriolis effect?

It results from observing motion in a rotating frame such as the spinning Earth. The rotation makes freely moving air and water appear to curve rather than travel in straight lines.