In physics, gravity (from Latin gravitas 'weight') is a fundamental interaction which causes mutual attraction between all things that have mass. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a result, it has no significant influence at the level of subatomic particles. However, gravity is the most significant interaction between objects at the macroscopic scale, and it determines the motion of planets, stars, galaxies, and even light.
The shape of two massive galaxies in the picture are distorted due to gravity.
The Leaning Tower of Pisa, where according to legend Galileo performed an experiment about the speed of falling objects
English physicist and mathematician, Sir Isaac Newton (1642–1727)
An illustration of the Schwarzschild metric, which describes spacetime around a spherical, uncharged, and nonrotating object with mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a body, until the discovery of the atom and particle physics. It was found that different atoms and different elementary particles, theoretically with the same amount of matter, have nonetheless different masses. Mass in modern physics has multiple definitions which are conceptually distinct, but physically equivalent. Mass can be experimentally defined as a measure of the body's inertia, meaning the resistance to acceleration when a net force is applied. The object's mass also determines the strength of its gravitational attraction to other bodies.
A 2 kg (4.4 lb) cast iron weight used for balances
Depiction of early balance scales in the Papyrus of Hunefer (dated to the 19th dynasty, c. 1285 BCE). The scene shows Anubis weighing the heart of Hunefer.
Galileo Galilei (1636)
Distance traveled by a freely falling ball is proportional to the square of the elapsed time.