In space, why do thrust and gravity behave differently when accelerating objects?

Question

If I attach the same engine to a 1,000 kg spacecraft and a 10,000 kg spacecraft in orbit, the 1,000 kg spacecraft will accelerate more quickly. If I drop a 1 kg rock and a 10 kg rock on the moon, they accelerate at the same rate. What is the difference?

I think what I may be asking is “why is gravity the a and not the f in f=ma.”

EDIT: BY all means please feel free to discuss, but I consider the question answered by u/mmmmmmBacon12345

mmmmmmm….. Bacon…..

In: 0

Answer 1

I’m no expert but I believe the official answer is “we don’t know.” Ask the top theoretical physicists and they can’t explain gravity other than “it just works the way we have observed.” Redditors, please correct me if I’m wrong.