What Is Acceleration of Gravity?

The acceleration of gravity on a free-falling object is called gravity acceleration. If m is the mass of an object, g is the acceleration of gravity. Gravity G can be expressed as G = mg ^[1] .

If a stone and an iron ball are allowed to fall freely from the same location, at the same height, and at the same time from the standstill, it can be observed that the speed of both objects increases uniformly and changes exactly the same, and they eventually reach the ground at the same time. This phenomenon shows that all objects that do free-falling movements at the same location on the Earth, despite having different weights, have the same magnitude and direction of acceleration during their fall. This acceleration is called free-fall acceleration, which is produced by the gravity of the object, also called gravity acceleration, which is usually expressed by the letter g. The acceleration of gravity is a vector, and its direction is always vertical downward. Its magnitude can be obtained experimentally. Experiments have shown that the magnitude of gravity acceleration varies slightly with its location on Earth. For example, g = 9.780 m / s ² at the equator, g = 9.832 m / s ² at the north pole, g = 9.807 m / s ² at sea level at 45 ° north latitude, and g = 9.801 m / s ² at Beijing. Usually, g is taken as 9.80 m / s ² when it is not specified. For rough calculations or instructions, g can be taken as 10m / s ^{2 [3]}

According to Newtonian physics, the expression for calculating the acceleration of gravity is given below. This calculation is important. Because the accelerometer cannot measure the acceleration of gravity, it must be calculated by the computer based on the position on the earth, ie ^[4]

To commemorate Galileo, the first physicist to measure the acceleration of gravity, the CGS unit (centimeter, grams, and seconds) of the acceleration of gravity is called "Gal". In the International System of Units, the unit of gravity acceleration is m / s ^{2 [1]}

The direction of gravity acceleration g is always

The earliest to measure the acceleration of gravity was Galileo. Around 1590, he used a slope to change the measurement of g to a small acceleration a = gsin , where is the inclination of the slope. Another way to measure gravitational acceleration is the Attwood machine. In 1784, G. Attwood connected heavy weights of the same mass with a rope and placed them on a smooth lightweight trolley, and then attached a much smaller weight m to a weight (Figure 2) . At this time, gravity drags the large mass to cause a slight acceleration.

After measuring a , g can be calculated. Later generations also measured g with pendulums and various excellent gravity accelerometers ^[7]

Gravitational acceleration of sea level at various latitudes (m / s ² ) ^[8]

In some modern science and technology issues, the influence of the rotation of the earth needs to be considered. More precisely, the falling acceleration g of an object is generated by the combined force W (Figure 1) of the gravitational force F (see universal gravity) and the centrifugal force Q (see relative motion) caused by the rotation of the earth. The size of Q is ^[9]

Accurate determination of the g acceleration g value is of great significance to metrology, precision physical metrology, geophysics, earthquake prediction, gravity prospecting and space science. For example, the uncertainty of g value of 1 × 10 ^-6 has an impact on absolute amps of 5 × 10 ^-7 ; the effect on absolute volts, force and pressure is 1 × 10 ^-6 ; The effect is 3 × 10 ^-4 K ^[10] .

Geophysical research requires observing subtle changes in the gravitational long gauge, the so-called length of g; this change may be due to crustal movement, the evolution of the internal structure and shape of the earth, the length of the dynamic constant in the solar system, and the gravity Change and more. Observing these changes requires that the measurement uncertainty of the g value be in the order of 10 ^-8 to 10 ^-9 . The observed change in g value may have a close relationship with earthquake prediction. According to reports from related parties, the change in g value corresponding to a magnitude VII earthquake is about 0.1 × 10 ^-5 m / s ² . At present, many countries are exploring the use of changes in the value of g as the measurement of earthquake prediction near gravitational acceleration ^[10] .

Gravity prospecting is the use of differences in the density of underground rocks and ore bodies to cause corresponding changes in ground gravity acceleration. Therefore, by measuring the change of g on the ground or at sea, we can indirectly understand the geological structure, ore body and rock body burial situation of underground density different from the surrounding rocks, and delineate their location ^[10] .