If the hammer and feather move at the same speed why do comet and the tail particles move at different speeds?
From this exhibition by an astronaut on the moon dropping a hammer and a feather and showing they move at the same speed, why do the particles of the comets tail move away from the comet, slow down ...
We know that nothing can have proper velocities larger than the speed of light in vacuum. But are there any objects in space that get close to it? Any comets, or other objects thrown by gravity or ...