GALILEO and MAROSZ's problem
https://www.youtube.com/watch?v=BsU4WupoaG4

Einstein's ROCKET and constant acceleration
https://www.youtube.com/watch?v=LUNBgQPF99w

FIRST STEP TO NEW PHYSICS
what if mass M will escape from own gravitation
https://www.youtube.com/watch?v=iHMYfYo9cXg