# Mass

Mass is, informally, the amount of material in an object. It is one of the core concepts of physics, especially mechanics.

## Formal Definition

Mass is a measure of the amount of matter a physical body contains. Mass is often confused with weight, but is not the same. While weight is a measure of the gravity on a body, mass is the amount of matter. Note that in a standard gravitational field, mass is directly proportional to weight.

## Units of Measure

• The SI unit for mass is the gram.
• Larger units include the kilogram (1000 grams), tonne (1000 kilograms), kilotonne (1000 tonnes), megatonne (1000 kilotonnes), etc.
• The imperial system has no measure for mass, as at the time it was popularized, the distinction between mass and weight had not been popularized.

## Related Formulae

• Momentum is calculated by $M=mv$, where $M$ is momentum, $m$ is mass, and $v$ is velocity.
• Thermal energy is calculated by $E=mh$, where $E$ is the thermal energy, $m$ is mass, and $h$ is heat.