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I have been hearing a lot about Newton's First Law of Motion, where an object will continue to be at rest or in motion unless it is compelled to change its state by external forces. So my question is, is it really possible for an object to be completely stationary in reality? Or is it identical to the idea of absolute zero, where it is impossible to achieve in reality? If absolute stationery is possible, how? If not, why so?

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  • $\begingroup$ Why do you need absolute stationarity? You might as well ask "is it every possible for an object to be moving at exactly 10 metres per second?" The probability of anything having some exact speed is vanishingly small. The comparison to absolute zero does not hold here, because obviously if I start moving at 10m/s in one direction and transition to moving at -10m/s, I will have transitioned through 0m/s. But if you're asking whether anything can have zero kinetic energy, then I understand the absolute zero connection $\endgroup$ Dec 29, 2021 at 15:45
  • $\begingroup$ @QuantumMechanic "The probability of anything having some exact speed is vanishingly small." Not at one instant in time when it's accelerating from 9.9m/s to 10.1m/s! $\endgroup$
    – DKNguyen
    Dec 29, 2021 at 15:47
  • $\begingroup$ There is no universal reference frame. This means that there is nothing with which you can measure an object's velocity against that all observers would agree on. $\endgroup$ Dec 29, 2021 at 18:03
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    $\begingroup$ @QuantumMechanic I was just being facetious. I stopped reading halfway through your comment to make my facetious comment. $\endgroup$
    – DKNguyen
    Dec 29, 2021 at 20:30
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    $\begingroup$ @DKNguyen I appreciate facetiousness $\endgroup$ Dec 30, 2021 at 2:20

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In order to define an object's speed you need to pick a reference frame.

If you pick the object's reference frame, than it is always going exactly $0.0000...$ mph, case closed.

If you pick another object's reference frame, then they'll only be going the same speed if some there is some friction/drag restoring force centered on $v = 0$. Example: a parked car relative to the earth's surface.

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Yes, it is possible.

Massless particles, of which the standard example is the photon, are in an absolute inertial frame and these are the only absolute intertial frames in GR.

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    $\begingroup$ How is this a good way of answering the question? You're bringing up concepts way more complicated than necessary. "can two objects be at rest relative to each other?" "well let's talk about general relativity" give me a break. The clout chasers on this site sometimes $\endgroup$
    – Señor O
    Dec 30, 2021 at 5:11
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    $\begingroup$ @Senor O: Because it is the best way of answering it? There's no need to understand the mathematics of General Relativity to appreciate that the light frame is an absolute rest frame. This is an outcome of both Maxwells theory of Electromagnetism and the null result of the Michael-Morley experiment on the rest frame of the aether. $\endgroup$ Dec 30, 2021 at 6:05
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    $\begingroup$ yeah guy comes in asking about if things can be stationary the best way to answer is "light cuz GR" that'll make sense to him LMAO. $\endgroup$
    – Señor O
    Dec 30, 2021 at 22:28
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In the theory of classical mechanics, objects have exactly defined speeds, so any object has a speed of exactly zero in its own reference frame.

However, in reality, classical mechanics has limitations. In particular, it breaks down at very small scales, which becomes relevant when you start talking about things being exact. In quantum mechanics, only eigenstates of observables have exact values for those quantities. Since momentum (and by extension, velocity) eigenstates are not normalisable, they are not physical, which means that particles cannot have exact momenta (or velocities).

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