Explain gravity 
 Gravity is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is the weakest of the four fundamental interactions namely the strong, weak, electromagnetic and gravity. However, it is the most significant interaction between objects at the macroscopic scale, and it determines the motion of planets, stars, galaxies, and even light. 
Gravity is most accurately described by the general theory of relativity that was proposed by Albert Einstein. The theory describes gravity not as a force, but as the curvature of spacetime, caused by the uneven distribution of mass, and causing masses to move along geodesic lines.
However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which describes gravity as a force causing any two bodies to be attracted toward each other, with magnitude proportional to the product of their masses and inversely proportional to the square of the distance between them.