Mass physics is the study of mass and its properties in relation to various forces. People who are unaware of the specific definitions often confused with mass with weight. Weight, however, refers to the amount of gravity required to pull an object down, whereas mass is actually related to the amount of matter inside a body, which remains unchanged regardless of environment. Mass itself is studied as both gravitational mass and inertial mass by mass physics.
Understanding the difference between weight and mass is important to understanding mass physics. Gravity is a force that all bodies in the universe exert on one another, and in the case of planets, like the Earth and Jupiter, this force is quite substantial and even keeps the moon in the Earth's orbit. The Earth’s gravity, acting on objects, pulls them down, and weight is the measure of the force of gravity that is required to keep objects on the earth. People are said to weigh less on the moon than they do on Earth because the moon doesn’t have as much gravity as the earth. The mass of an object, on the other hand, is the same, regardless of the surrounding gravitational situation.
The concept of mass can seem difficult to comprehend, but it is simply the amount of “stuff” that makes up an object or being. Mass physics divides mass into gravitational mass and inertial mass. Gravitational mass is measured by putting an object with an unknown mass on a set of scales with an object with a known mass on the other side. The gravitational force on each object will be the same, which allows the mass of the unknown object to be determined using the known mass of the other object.
Inertial mass is related to Newton’s law of motion. This law states that force equals mass multiplied by acceleration (F=ma), and is therefore logically equivalent to stating that mass is force divided by acceleration (m=F/a). Mass physics defines inertia as an object’s resistance to movement when a force is applied to it. By applying a known force to an object and using Newton’s equation, the inertial mass of an object can be found. The inertial mass always seems to be equal to the gravitational mass, as far as our measuring capabilities allow us to determine.