# Blog

## Gravitational force and moment of Inertia of orbiting bodies

Another question is about the gravitational force. If all subjects (masses) onboard International Space Station have the colossal moment of Inertia and their moments do not depend on their speeds but only their rotation radii in according to this formula I = m*r , then what gravitational force should be to overcome such great moments of Inertia and pull those masses to the Earth center?!

It is known that spaceships or International Space Station or another orbiting body needs to decrease its speed to get into a lower orbital trajectory. However, how can it happen if all bodies (masses) which orbit the Earth have the tremendously large moments of Inertia and their moments do not depend on their speeds? How large should the gravitational force be to overcome their moments of Inertia?

## About relativity of Inertia

When one tells that all physical properties are the same in one frame of reference (physical system), it just a description of our observations. In other words, it does not explain any physical nature of, say, the situation when astronauts can easily move various subjects (masses) onboard International Space Station, even though these masses including astronauts themselves have the colossal moments of Inertia as it is analyzed in another post “Rethinking the classical mechanics Part 5 of 10”. We just see that astronauts easily move distinct subjects (masses), so we say all physical properties are the same in International Space Station. However, how it happens that astronauts may easily move those subjects when an observer on the Earth surface cannot move them because those subjects have the colossal moment of Inertia with respect to him/her. What PHYSICALLY happens with astronauts and other orbiting bodies (masses) that they (astronauts) can easily move those masses inside International Space Station, but an observer on the Earth surface could not move the masses because the masses have the colossal moments of Inertia with respect to the observer?!