In a range not too high from the earth's surface, the acceleration of a particle due to the earth's gravity is called "gravitational acceleration". It can also be said that the acceleration of an object due to gravity is called "gravity acceleration". For an object close to the ground, because other celestial bodies are far away from it, the gravity of other objects on the earth is very small, so the gravity of the reading object refers to the gravity of the earth and the direction points to the center of the earth. Near the ground, the acceleration of gravity of any object is the same in the same place, but slightly different in different places. This acceleration is represented by the letter G, which is determined to be near the equator, and g = 9.78m/S2；; The earth's north pole g = 9.83m/S2；; Beijing g = 9.80m/s 2; Shanghai G = 9.79 m/s 2. G = 9.8 m/s 2 can be taken approximately in general inaccurate calculation. The motion of an object thrown vertically is a uniform linear motion, which is only influenced by gravity (ignoring air resistance), and its acceleration is also gravity acceleration. But when the object starts to be thrown vertically, the direction of acceleration is opposite to the initial velocity. If the vertical direction of a moving object is positive, the acceleration direction should be negative, that is, a=-g=-9.8 m/s 2. The acceleration of gravity in the above places is at the average sea level. At a high altitude from the ground, the acceleration of gravity is significantly reduced. Because the earth is an elliptical sphere, its polar radius is about 0.3% smaller than the equatorial radius, so the gravity of the same object in different regions is slightly different. When an object near the ground rotates with the earth, gravity will inevitably provide its centripetal force, so the gravity of the same object in different areas is not only slightly different in value, but also does not point to the center of the earth. So the acceleration of gravity in different areas is slightly different, and the direction does not point to the center of the earth.