Force
A force is an interaction that changes the motion of an object. Newton defined it through its effect rather than its substance: an object keeps moving in a straight line at a steady speed unless a force acts on it, and the force applied equals the object's mass times the acceleration it produces. Forces always come in pairs, so pushing on something means being pushed back on with equal strength in the opposite direction. In modern physics the fundamental forces are described as interactions carried by fields rather than as pushes and pulls between objects.
Why it matters
It is the first quantity in physics defined purely by what it does rather than what it is, and that move set the pattern for everything that followed.
Also written: forces
Where it comes up
Sources
- Force English Wikipedia
- Newton's laws of motion English WikipediaThe three laws that give force its working definition.
- Force Britannica
