Force (physics)

Force (xoog in Somali) is an effect arising from the interaction of two objects that can change the motion of an object, the direction it moves in, or its form. It has both magnitude and direction, which is called a vector quantity. The standard unit of measurement is the newton (N).

The concept of force is central to classical mechanics. When the forces acting on an object are balanced, the object will remain stationary or continue to move with constant velocity and direction. When they are unbalanced, the object's motion changes—this is acceleration.

Newton's Laws

Isaac Newton summarized the relationship between force and motion in three laws. The first law states that an object not acted upon by unbalanced forces will remain in its state of motion. The second law relates the net force acting on an object to the change in its motion; the most common form is F = ma, where m is mass and a is acceleration. The third law states that every force has an equal and opposite force acting on the other object.

Types of Force

Forces can be divided into contact forces and action-at-a-distance forces. Contact forces include normal force, tension, and friction. Action-at-a-distance forces include gravity, electromagnetism, and the strong and weak nuclear forces. In modern physics, four fundamental interactions have been identified: gravity, electromagnetism, the strong nuclear force, and the weak force.

Measurement and Combination

One newton is the force that accelerates a mass of one kilogram at one meter per second squared. When multiple forces act on an object, they are combined using vector addition, yielding the net force. Force diagrams are used to analyze each force individually.

Modern Perspectives

In modern physics, force is sometimes regarded as secondary to more fundamental concepts. Quantum mechanics and general relativity are based on energy, momentum, and the geometry of spacetime rather than force as such. For example, Einstein's general relativity describes gravity not as an ordinary force but as the curvature of spacetime.