Several times in our daily lives, we come across situations in which we drop some object, be it an eraser, a pen, or even a glass. This downward movement has intrigued scientists for many, many years (about 2,000 years). According to the history of science, the first scientist to propose explanations for this fact was Aristotle, but the one who best clarified the phenomenon was Galileo Galilei.
After several experiments, Galileo managed to reach the conclusion that, for objects close to the Earth, and disregarding the resistance of air, any object falls with the same acceleration. This acceleration was called gravity acceleration.
Isaac Newton, who was interested in free fall movement, presented concise explanations about the existence of gravity acceleration. He enunciated that where there was acceleration there would be a force, because if an object falls with acceleration, it is because the Earth exerts a force on it - called weight –, which is represented by P.
According to his experiments, Newton realized that the force weight has the same direction as a force that passes through the center of the Earth, that is, the direction of the weight vector is facing the center of the
Earth, regardless of the location of the object in the vicinity of the Earth. In the figure above, we have an illustration of the weight force acting on an object near the Earth, in which the weights of the bodies have different directions, but both are oriented towards the Earth's center.Because the Earth is huge (when compared to bodies with very small mass in relation to their size), we can admit that the bodies, located close to the earth's surface, have weight with the same direction and the same sense.
If we leave an object with pasta m in the vicinity of the earth's surface, in a region where there is a vacuum, we can verify that the resulting force acting on the body is, in fact, its own weight. Thus, based on the Newton's second law, we have:
⇒ 
Therefore, we can say that the weight of a body or object, when placed near the surface of a planet, satellite or star, equals strength with which this body is attracted to them.
By Joab Silas
Graduated in Physics