Apples fall from trees to the ground because of gravity, and we do not float into the universe because of the gravity of the earth, so is gravity gravity? Not really.
Gravity is one of the four basic forces known in the universe, and any two objects with mass have mutual gravitational effects, such as the two cups on the table, which also have mutual gravitational effects, but because they are extremely weak, they cannot be detected. So what is gravity? Gravity is not actually equal to gravity, but it is closely related to gravity. In fact, gravity is the force generated due to the earth's gravitational attraction to the object, and its calculation formula is F =mg, m is the mass of the object, g is the acceleration of gravity, and the acceleration of gravity on earth is 9.8m/s. The mass of the object does not change, but the acceleration of gravity changes, so on different planets, the gravity of the object is different.
Gravitational force is F=GMm/R, G is the gravitational constant, M is the mass of the Earth, m is the mass of the object, and R is the radius of the Earth.
From the calculation formula, it can be seen that gravity is not exactly equal to gravity, which is only related to the mass and distance of the two objects. If we think carefully about the relationship between gravity and gravity, we will find that the gravitational force of objects on Earth is actually not the same, and the first factor that leads to this difference is the location. The Earth is a sphere, but it is not a standard sphere, and to be precise, the Earth should be considered an ellipsoid. At the North and South Poles, the Radius of the Earth is about 6356.9 km, while at the equator, the radius becomes 6378.5 km.
Gravity is inversely proportional to the square of the distance, so the farther away the distance, the smaller the gravitational effect of the two objects, and it can be calculated that in the equatorial region, the gravitational force on the object is about 1.5 ‰ less than in the polar region.
The equatorial region is subjected to less gravity than the North and South Poles, but it is not only distance, there is another very important factor, that is, centrifugal force. The Earth is not a stationary planet, it is in rotational motion at all times, and its rotational angular velocity can reach 15 degrees per hour, so objects located on the Earth will also rotate with the Earth. However, not everywhere objects will rotate with the earth, and objects located at the north and south poles will not, so at the north and south poles, gravity is equal to gravity.
On Earth, the fastest place with the fastest rotational line is the equator, which can reach 1670 kilometers per hour, so the outward centrifugal force of objects located at the equator is the largest, so the gravitational force of objects in the equatorial region is equal to gravitational force minus inertial centrifugal force.
It should be noted that the centrifugal force does not actually exist, it is only a virtual force, in fact, the force generated to maintain the circular motion is the centripetal force, and the reason why it is expressed here in terms of virtual centrifugal force is to make it easier to understand and calculate. Gravitational force is GMm/R, while inertial centrifugal force is mω R, and the ω in it is the angular velocity of rotation. After calculation, it can be calculated that due to the influence of the rotation of the Earth, the gravity in the equatorial region is about 3.5 ‰ less than the north and south poles, and coupled with the gap of 1.5 ‰ due to the distance, it can be concluded that the gravity in the equatorial region is about 5 ‰ less than the north and south poles.
There are differences in earth's gravity, so buy gold in the equatorial region and then run to the North and South Poles to sell it, making a proper profit of 5‰.
However, although the idea is good, it has no practical value, because first of all, there is no gold store in the North and South Poles, and you need to force a buyer to go to the North and South Poles to trade with you. Secondly, the gold buyer must have just switched from selling vegetables, so that he will use a spring scale to weigh gold, while professional gold merchants use balances, which are the same everywhere. On the earth, the gravity of different locations is not the same, so is it possible for gravity to change in the same location? Of course it is possible, and it is changing all the time, but the change is very small.
The factors that cause a change in gravity at a site are not within Earth, but beyond Earth.
The Earth is not a lone star, there are other celestial bodies around the Earth, these celestial bodies have a gravitational effect on the Earth, and the magnitude of the gravitational force on the Earth objects changes, and the magnitude of the gravitational changes is related to the position relationship between the object and the extraterrestrial object. For example, the object located on the sun side of the earth, the direction of the earth's gravity and the sun's gravity is the same, so the gravity will increase slightly, and the object located on the earth's sunny side, because the sun's gravity and the earth's gravitational direction are opposite, so the gravity will be reduced, but the impact is very small, less than one in ten million, that is to say, ten million pounds of objects will only change by 1 pound of weight due to the gravitational force of the sun. In fact, the object that has the greatest impact on the earth's gravity is not the sun, but the moon, because it is close enough to us that its gravitational impact on the earth can reach about 2 times that of the sun, that is, two millionths.