**GREVYT PRESS FREQUENTLY ASKED QUESTIONS**

Q. Did you know that scientists agree that it is impossible to solve an unrestricted *n*-body gravitational problem?

A. I learned it for the first time from my physics teacher at the high school. That was long time ago. However, I was skeptical.

Q. In e-book *N Bodies - No Problem* is presented an unrestricted solution of *n*-body gravitational problem. However, the e-book also says that there are limits on gravitation. Please explain.

A. In the simulations at this web site, which are based on the solution in the e-book, you can enter any values for the masses, initial positions, and initial velocities of the bodies and you will receive mathematically and geometrically sensible results. That is what 'unrestricted' means. However, gravitation has physical limits. Examples: there is no negative mass; acceleration by gravitation cannot be too large; (I do not know the limit).

Q. How were technically developed the models for *n*-body simulation on this web page?

A. They are Java 2 applets developed with * Easy Java Simulations 3.1; 3.3* (by Francisco Esquembre).