# Inertial and Gravitational Mass

*Most recent answer: 07/30/2020*

Q:

Hello,I would like to ask about gravitational mass.I know inertial mass is changing by motion (speed) according to m=mo/(1-v2/c2)^0.5And also that is inertial mass which sits in E=mc2.If the statements above is correct, now how about gravitational mass? Does it change with motion (speed)? And what mass should be used for general gravitational formula F=GmM/r2? should we use mo (rest mass) regardless of speed of the object? Or should we use m=mo/(1-v2/c2)^0.5 to substitute in F=GmM/r2?In other words does mass equivalence principle (inertial mass=gravitational mass) hold in hight speeds?Thank you

- Ebi (age 39)

Australia

- Ebi (age 39)

Australia

A:

Yes, the inertial and gravitational mass are the same. Think of a little ball with layers spinning opposite directions, just s we don't even have to think about angular momentum. It's got some inertial mass that you can measure. In a gravitational field, it will drop just like anything else. If the gravitational mass ere different from the inertial mass, it would not drop at the same rate. We'de have a way of detecting a uniform gravitatinal field. That would violate the equivalence principle, which has been well confirmed by all the confirmations of General Relativity.

Mike W.

*(published on 07/30/2020)*