Physics

The capacity to do work, taking forms such as kinetic energy (associated with motion) and potential energy (associated with position or configuration, such as height in a gravitational field). The total energy of an isolated system is conserved: energy changes form but is never created or destroyed.

A push or pull interaction between two objects, capable of changing an object's velocity. Newton's three laws of motion describe how forces and motion relate: a body keeps its state of motion unless acted on by a net force (first law), net force equals mass times acceleration, F = ma (second law), and forces between two bodies are equal and opposite (third law).

The attractive force between any two masses. Newton's law of universal gravitation describes it as proportional to the product of the two masses and inversely proportional to the square of the distance between them. Near Earth's surface this produces a roughly constant downward acceleration of about 9.8 m/s^2 on falling objects.

The product of an object's mass and velocity, a vector quantity describing the 'quantity of motion' it carries. In a closed system with no external forces, total momentum before and after an interaction such as a collision is conserved, even when kinetic energy is not (as in an inelastic collision).

The change in an object's position over time relative to a reference frame. Kinematics describes motion using position, velocity (the rate of change of position) and acceleration (the rate of change of velocity), without yet asking what causes it.