Newton discovered the law of gravitation, but he himself did not know the value of the gravitational constant G. By measuring the mass of the two objects, measuring the distance between the two objects, and then measuring the attraction between the objects, you can measure this constant by substituting the law of universal gravitation. But because the masses of ordinary bodies are too small, the attraction between them cannot be measured, and the masses of celestial bodies are too large, and the mass cannot be measured. Therefore, more than 100 years after the discovery of the law of gravitation, the constant of gravitation still does not have an accurate result, and this formula is still not a perfect equation. It was not until more than 100 years later that Cavendish, a British man, cleverly measured this constant by using a torsion scale.<br><br>This is a model of a Cavendish torsion scale and the main part of the torsion scale is this T-shaped light and strong frame, which is hung upside down under a quartz wire. If two equal and opposite forces are applied to both ends of the T-frame, the quartz wire will twist at an Angle. The greater the force, the greater the Angle of torsion. In turn, if the Angle of the T-frame is measured, the size of the force on both ends of the T-frame can be measured. Now a small ball is fixed at each end of the T-shaped frame, and a large ball is placed near each ball, and the distance between the two balls can be measured more easily. According to the law of gravitation, the big ball will attract the small ball, and the T-frame will be twisted, as long as the Angle of torsion is measured, the size of the gravity can be measured. Of course, since gravity is so small, the Angle of the twist will be small. How can we measure this Angle? Cavendish installed a small mirror in the T-shaped frame, shining a beam of light into the mirror, the light reflected by the mirror to the distant scale, when the mirror and the T-shaped frame together with a small rotation, the light spot on the scale will have a large movement. In this way, a small into a large effect, by measuring the movement of the light spot, measured the T-shaped frame in the placement of the ball before and after the torsion Angle, so as to determine the gravity of the big ball on the small ball at this time. Cavendish used this torsion balance to verify Newton's law of universal gravitation and to determine the value of the gravitational constant G. This value is very close to the value determined by more scientific methods in modern times.<br><br>Cavendish's G value of 6.754×10^-11 is now accepted as 6.67×10^-11. It should be noted that this gravitational constant has a unit: its unit should be multiplied by the kilogram of the two masses, divided by the square of the distance m, to obtain the unit of force Newton, so it should be N·m² / kg².<br><br>N. G = 6.67 * 10 ^ 11 m squared/kg squared<br><br>Because the value of the gravitational constant is very small, so the general mass of the gravitational attraction between objects is very small, we can estimate that the gravitational attraction between two students with a mass of 50kg is about 6.67×10^-7N when the distance is 0.5m, such a small force we can not feel. Only the gravitational pull of very massive objects on ordinary objects can be felt, such as the Earth's gravitational pull on us is roughly our gravity, and the moon's gravitational pull on the oceans causes tidal phenomena. The gravity between celestial bodies is very amazing due to the large mass of the planet: for example, the sun's gravity on the Earth reaches 3.56×10^22N.