Force

In physics, a force is a push or pull or a twist between objects. It is called an interaction because if one object acts on another, its action is matched by a reaction from the other object.^[1] This idea is known as Newton's third law,^[2] where action and reaction are "equal and opposite" ^[3] (matched). The objects are just the things the force acts between. Different forces act between different sorts of object. For example, gravity acts between objects with mass, like the sun and the earth. Another example is electromagnetic force, which acts between objects with charge, like an electron and the nucleus of an atom. Gravity and electromagnetic force are two examples of forces.

A force changes the state of an object (some physical quantity changes) or, strictly, the states of two objects, since the force is an interaction. For example, a force causes an affected object to be pushed or pulled in a certain direction. This changes the object's momentum. Forces cause objects to accelerate, add to the object's overall pressure, change direction, or change shape. Because the magnitude and direction of a force are both important, force is a vector quantity. The strength of a force is measured in newtons (N). There are four fundamental forces in physics.

A force is always a push, pull, or a twist, and it affects objects by pushing them up, pulling them down, pushing them to a side, or by changing their motion or shape in some other way.

1. ↑ "Any single force is only one aspect of a mutual interaction between two bodies." (Halliday, Resnick & Krane 2001, pp. 78–79) harv error: no target: CITEREFHallidayResnickKrane2001 (help)
2. ↑ C. Hellingman (1992). "Newton's third law revisited". Phys. Educ. 27 (2): 112–115. Bibcode:1992PhyEd..27..112H. doi:10.1088/0031-9120/27/2/011. S2CID 250891975. Quoting Newton in the Principia: It is not one action by which the Sun attracts Jupiter, and another by which Jupiter attracts the Sun; but it is one action by which the Sun and Jupiter endeavour (try) to come nearer together.
3. ↑ Newton, Isaac (1687). Philosophiae Naturalis Principia Mathematica (in Latin). contrariam semper & aequalem