In physics, force is defined as any interaction that can cause an object to change its velocity, and so to accelerate or slow down. Force is a vector quantity, meaning that it has both magnitude and direction.

  • Forces can be either contact forces or non-contact forces.
    • Contact forces are forces that act when two objects are in contact with each other. Examples of contact forces include friction, tension, and normal force.
    • Non-contact forces are forces that act between objects that are not in contact with each other. Examples of non-contact forces include gravity, electromagnetism, and the strong nuclear force.
  • Forces can bind objects together or push them apart, affecting their state of motion. Force can therefore be described intuitively as a push or a pull with magnitude and direction, making it a vector quantity.
  • Whenever there is a push-pull interaction between two objects, forces are exerted on both. Once the interaction ceases, the forces no longer act, and the momentum of the objects continues unchanged.
  • Objects, bodies, matter, particles, radiation, and space-time are all in motion.
  • On a cosmological-scale, concentrated matter in planets, stars, and galaxies leads to significant push-pull interactions.
  • Motion signifies a change in the position of the elements of a physical system including translational motion, rotational motion, vibrational motion, and oscillatory motion.
  • The push-pull interactions between things are explained by the interplay of forces.
    • The existence of forces explains how objects interact with each other throughout the entirety of the natural world.
    • Forces generate motion and can cause changes in velocity for objects possessing mass.
    • Changes in velocity encompass various scenarios, such as initiating motion from a state of rest, accelerating, or decelerating.
  • There are four fundamental forces that account for all the forms of pulling and pushing between things in the Universe.
    • The electromagnetic force is responsible for interactions between charged particles, such as electrons and protons, and is fundamental to electrical and magnetic phenomena.
    • The weak nuclear force is involved in processes like radioactive decay and plays a role in the interactions of subatomic particles.
    • The strong nuclear force binds atomic nuclei together and is responsible for the stability of matter. It is the strongest of the four fundamental forces, but it has the shortest range.
    • Gravity governs the interactions between massive objects and is responsible for phenomena like planetary motion and the attraction of objects towards Earth.
  • Read more about the four fundamental forces here.