In the study of dynamics, it is very important to keep in mind the definitions of what constitutes mass of a body and force applied to a body.
Mass : is a physical quantity that is assigned to a body, obtained after comparing it with the mass of a standard body. This can be the kilogram – standard, which is a small block of platinum (90%) and iridium (10%). This small block is located at the International Institute of Weights and Measures in Sèvres, near Paris, France. By definition it has a mass of one kilogram, represented by the letter kg. In the International System of Units the unit of mass is the kilogram, kg. It is important to point out that the mass of a body does not depend on its position in space, that is, the mass is always the same, whether it is on Earth or on the Moon.
Force: when we talk about strength, we always relate it to the effort we make to perform everyday activities, that is, muscular effort. Force is a vector quantity that has magnitude, direction and sense. Forces can be contact, field, electrical and magnetic in nature. Force is the agent capable of changing the state of rest or movement of a given body, that is, it is the cause that produces a change in velocity in a body. In the International System of Units the unit of force is the newton (N), named after Isaac Newton.
