BlackDog

i think i didn't ask the question right. my question is, is it possible to define acceleration with only one object in the universe? lets suppose that object is an atom. the reason for my question is, if it'd be possible to define acceleration with only one object, i would understand that acceleration is not relative. if it cannot be defined without two objects, it must be relative, right? of course i understand if we have two objects, such as the pendulum and earth, there would be acceleration. even in an universe with two objects, if we move the objects away from each other, we must have motion, and as their relative motion goes from 0 to x velocity, we would have acceleration. but what if we don't have two objects? -shami

wait, isn't it true that without my consciousness, nothing exists to me, let alone time? this is philosophy, how can it be physics? -shami

so is it fair to say that in an empty universe with only one object, the object can't be moving along a straight line, so velocity cannot be defined, yet it can have acceleration? you see, the example you gave me also include two objects, me and a ball, to explain the effect of acceleration. still seems very weird to me. sorry for keep asking questions on the same subject. -shami

i think the answer "man" also works for "in the shortest amount of time." -shami

oops... sorry i didn't notice that "physics expert" title under swansont! (how dare i am to think he is wrong... stupid me). thanks spyman. okay, now i understand that with a focault pendulum, it's possible to tell whether something is spinning or not. so that means spinning is absolute! that means earth's rotation on its axis does not affect the relativity of moon's orbit in respect to earth. but why is spinning absolute and not relative? now i'm more confused. should have studied physics (would have failed though). ah... going back go google. -shami

still waiting for an answer to this question... anyone? i don't think that pendulam answer was correct. besides, what if the objects are not earth and moon, but two balls? hmm... -shami