# What is the Difference Between Gravitational and Inertial Mass?

## Answer #1

Level 2 (without higher mathematics)

Answered by Alexander Fufaev

**Inertial mass** \( m_\text{t} \) is the constant of proportionality in *Newton's second law of motion*: \(F~=~m_\text{t} \, a\). Inertial mass provides resistance to the change in the state of motion of a body. The state of motion changes when the *direction* or *acceleration* of the body changes. **Gravitational mass** \(m_\text{s}\) refers to gravity and influences how strong the gravitational force \(F_\text{g} ~=~ m_\text{s} \, g\) is. Here \(g\) is the gravitational acceleration.

Experiments have shown that inertial mass \(m_\text{t}\) and gravitational mass \(m_\text{s} \) agree to an accuracy of \(10^{-13}\) and are thus assumed to be equal: \(m_\text{t} = m_\text{s} \).