Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.

How is mass defined? How is mass measured?

Why are the inertial mass and gravitational mass of an object the same? We don't know. It seems possible to imagine a world in which they aren't exactly the same.

This question is one of the deep mysteries of the universe.

Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.