Rest mass

Definition

Rest mass is the mass of an object when it is at rest relative to an observer. It is an invariant quantity in special relativity, meaning it does not change regardless of the object's velocity.

5 Must Know Facts For Your Next Test

1. The rest mass is denoted by $m_0$ and remains constant regardless of the object's speed.
2. Unlike relativistic mass, rest mass is invariant and does not depend on the reference frame.
3. In special relativity, rest mass is essential for calculating energy using the equation $E = m_0 c^2$.
4. Rest mass plays a crucial role in determining relativistic momentum, given by $p = \gamma m_0 v$, where $\gamma$ is the Lorentz factor.
5. The concept of rest mass helps distinguish between different types of particles, such as photons which have zero rest mass.

Review Questions

• What is the difference between rest mass and relativistic mass?
• How does rest mass affect the calculation of energy in special relativity?
• Why is rest mass considered invariant in special relativity?

Related terms

Relativistic Mass: The effective mass of an object in motion, which increases with velocity according to special relativity.

Lorentz Factor: A factor $\gamma = (1 - v^2/c^2)^{-1/2}$ that describes how time, length, and relativistic momentum change for an object moving at velocity $v$.

Invariant Mass: Another term for rest mass; it's a fundamental property that remains unchanged regardless of the object's state of motion.