When is an object considered to be at rest?
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$\begingroup$ Are you asking if you can walk to a store then back home and end up having an average velocity of 0? $\endgroup$– Jimmy360Commented Mar 9, 2015 at 9:08
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$\begingroup$ I'm trying to clarify the meaning of a object being at rest. Some one told me an object is at rest when velocity is equal to zero but I don't believe it. $\endgroup$– Harrison TranCommented Mar 9, 2015 at 9:09
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1$\begingroup$ Why dont you believe it? its not about believing ,its the defination of the word ''rest''. when the object's position isnt chnging with time then it is at rest. $\endgroup$– PaulCommented Mar 9, 2015 at 9:34
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2$\begingroup$ I feel like version 3 of the question is a different question than version 1. As I read the question as it's currently written, I think the question is about relative velocities (ie, how do we define "at rest" in an inertial reference frame) which is vastly different than whether $\bar v=0$ constitutes "at rest" even when speed is nonzero $\endgroup$– SeanCommented Mar 9, 2015 at 12:08
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$\begingroup$ $\uparrow$ @Sean: You've got a point. Harrison Tran: Please edit the post to clarify your question. $\endgroup$– Qmechanic ♦Commented Mar 9, 2015 at 13:26
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1 Answer
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Yes you can. An object moving in a circle has 0 overall velocity because the net displacement is 0, but the object still has speed because it's covering distance. EDIT: The answer to the modified question is that there is nothing known as being "absolutely at rest". Velocities are relative, as was demonstrated by Gallileo, and time is relative as well, as was pointed out by Einstein. Only acceleration is absolute, because the distinguishing characteristic is the inertia experienced by an accelerating object which allows one to know that the frame of reference of the object is non-inertial. Also note that if you are talking about instantaneous velocity, then when this equals 0, the object is at rest.(relative to the observer)
answered Mar 9, 2015 at 9:05