# Gravity trivia: Why do planets have gravity?

Why does the planet have gravity? Gravitation is a kind of basic interaction in particle physics, a kind of force. In terms of direct effects, gravity comes from the mass of matter, relative motion of objects, acceleration, etc.

(1) Gravity comes from mass. The mass mentioned here is gravitational mass, which is conceptually different from inertial mass, but from the current experiments and observations, the two are equal in value. The greater the mass of the object, the stronger the gravitational effect on other objects.

(2) Gravity comes from relative motion. The physical quantity that measures relative motion is speed. The greater the speed of an object, the greater the mass of the object observed by the observer, and the stronger the gravitational effect caused by the object.

(3) Gravity comes from the speed of the change of the object’s movement speed. The physical quantity that measures how fast the speed of an object changes is acceleration. In general relativity, acceleration and gravitational field are equivalent, so the faster the velocity of the object changes, the stronger the gravitational effect will be.

In short, gravity comes from the gravitational field. But in essence, according to general relativity, gravity is a bending effect of the mass of an object on space-time. It is a ripple caused by an object in the background of space-time, causing the object to spontaneously move toward the center of the vortex of this ripple. Trend, and this is the gravity in the theory of relativity. Since all objects cannot exist without the background of time and space, they will produce different degrees of ripples on the background of time and space, so they all have a tendency to be pulled toward the center of the vortex of ripples. Therefore, gravity is inherent in nature and is inherent to matter. Attributes.

A planet is a celestial object, and its source of gravity can be understood according to the above description, and the same applies.

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