force

In physics, force is an interaction that can cause an object of mass to accelerate, change its velocity, or deform. Forces are vector quantities, characterized by magnitude and direction as well as the point of application. They can act at a distance or through contact.

The SI unit of force is the newton (N). By definition, one newton is the force required to accelerate a one-kilogram mass at one metre per second squared: F = m a.

Forces can be classified as fundamental and non-fundamental. The fundamental forces are gravitation, electromagnetism, the strong nuclear force, and the weak nuclear force. Non-fundamental forces arise from interactions between bodies, such as contact forces like friction, normal force, tension, and spring force, as well as non-contact forces such as gravitational or electromagnetic forces acting at a distance.

Newton's laws describe how forces affect motion. An object at rest or moving with constant velocity remains so unless acted on by a net external force (Newton's first law). A net force causes acceleration according to F = m a (Newton's second law). The net force on a body is the vector sum of all forces acting on it.

Equilibrium describes a state where the vector sum of forces is zero, resulting in no acceleration. Friction opposes motion between surfaces and depends on the interaction of the surfaces and the normal force.

Measurement and applications: Force is measured with devices such as spring scales and force sensors. Understanding forces is essential in engineering, physics, biomechanics, and everyday activities.