Gravitational & Inertial mass
At this point, we have finished our presentation of Einstein’s special theory of relativity. It is called special because it is restricted to physics described in inertial reference frames (constant velocity).
It took Einstein 11 years to generalize relativity so that it applied to descriptions of physics in ANY reference frame.
Starting question: Why do we need two kinds of mass?
- Inertial mass: the measure of how hard it is to accelerate a body.
- Gravitational mass: the measure of how big of a gravitational force the body exerts on other bodies.
Experiment: measure the difference between these masses.
- Eotvos (1909): no difference to 5 parts in 109
- Dicke (1964) : no difference to 3 parts in 1011