# Some common forces in nature

## Force weight

It is the force with which the earth attracts the bodies. When a body is in free fall, it increases approximately 10 m / s every second. As we have seen, the magnitude that measures the variation in body velocity as time goes by is the acceleration. We have seen that the acceleration of gravity has a value of: The value of the acceleration of gravity is not the same for every star in the universe.

The greater the value of the acceleration of gravity, the greater the force that the planets exert to attract other bodies, the more it will be attracted to the planets. Therefore, weight is directly proportional to body mass and acceleration of gravity..

 Thus, we can express the weight of a body P through a mathematical relationship, in which weight corresponds to the product of body mass (m) by the acceleration of gravity at location (g).

That is: An important question is to understand what is the difference between weight and mass.

Pasta It is a property of bodies related to the amount of matter the body has. The mass does not depend on where the body is. The unit of measurement of mass in the International System is the kilogram (kg). O Weight it depends, besides mass, on the value of the acceleration of local gravity, and is a force whose unity in the International System is the Newton (N).

Imagine two identical bodies, one on Earth and one on the Moon. They have the same mass, but the body on the Moon, where gravity acceleration is worth 1/6 of terrestrial gravity acceleration, is 6 times less than of the body that is on earth.

Here's an example:

On Earth, the weight of a person weighing 60 kg will be: On the moon, the weight of this same person will be: Note that the phrase “My weight is 50 kg!”, Although very common, is wrong. The correct is to say: "My mass is 50kg".

Another very common unit for measuring forces is the kilogram-force (Kgf). A Kgf is a force with which the Earth attracts one kilogram at sea level and at 45º latitude. Therefore, when a person weighs himself, if his mass is 50 kg, it can be said that he is 50 kgf in weight.

 We represent the weight force at the center of the body's gravity, always vertical downwards.