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"A state of rest" is a relative term. Relative means - measured in comparison to the things around it. When you sit in a train and sip from a cup of coffee, you can do so because the cup is still relative to you even though both of you might be hurtling through the countryside at 200 km/h. For most experiments, objects can be considered "at rest" if they ...


6

Revolving around the sun is equivalent to free fall around the sun, so the revolution allows you not to 'feel' the sun's gravity. The rotation of the earth is something that can be measured: (i) a centrifugal force which is a small offset on gravity, and (ii) causes the coriolis force. Both these are small effects, so can often be ignored for laboratory ...


4

Both concepts are mathematical in character and they ultimately describe the same characteristics or situations. "Invariance" is a more technical word because it says "what has to be equal to what" for us to say that the symmetry exists. In particular, the "invariance under a symmetry transformation" means that an object, like the action $S$, has the same ...


3

In condensed matter "bulk" does not refer to the dimensionality of the problem but the location in the material. It refers to the volume of the crystal, as opposed to, e.g., surface effects. Many organic conductors behave as 1D systems, yet you can talk about bulk properties. Copper oxide superconductors have a 2D physics. However, often you will find ...


2

"Rest, in physics, refers to an object being stationary relative to a particular frame of reference or another object." - Wikipedia (emphasis mine) While on Earth, the planet is often treated as the default frame of reference. It is not a perfect frame of reference, but for many purposes it is good enough. Since there is no absolute frame of reference, ...


1

When you push a rope, it has that bulk property to easily change its shape and bend without producing much of a reaction force. But if you pack the rope in a very narrow hollow cylinder (an impossible ideal case indeed) where the rope won't have the freedom to bend, and then push it, it will get compressed first filling up gaps in the fiber binding but after ...


1

V may represent true mass flow, or the flow of density, rather than simply the flow of volume. Q may represent a flow of volume unadjusted for density. TSI toolmaking co. uses Q as "standard flow rate", but they make an instrument that converts Q to "VolumetricFlow" by applying a density correction. See the link for the formula. Another example of this ...


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Every phase transition has an order parameter: something that vanishes above the transition temperature and is finite below. In superconductors, the order parameter is a complex quantity related to the superconducting gap: $\Delta = |\Delta| e^{i \phi}$. In BCS theory, there is a self-consistent equation for the gap: $\Delta_k = -\sum_q V_{kq} ...


1

Two different wave concepts are being confused here and called an EM wave. There exists electromagnetic radiation from light to radio waves to gamma rays , and for that see this answer of mine which explains how the classical wave of the Maxwell equations is an emergent phenomenon: it is built up by photons. And there exist the alternating currents in ...


1

Don't confuse theory with reality. Electromagnetic theory (i.e., the theory of Maxwell) talks about waves of electric and magnetic field strength. The standard model of particle physics talks about photons---discrete particles/packets of energy---whose appearance are governed by probability densities that obey wave-like laws. As far as we know, gamma rays ...


1

The states of charmonium are treated as bound states of a charmed quark ($c$) and its anti-quark ($\bar{c}$). Since the binding energy of the $c-\bar{c}$ system is relatively small, compared to the rest energy of the charmed quarks, it is a reasonable starting point to analyze the states using the non-relativistic Schroedinger equation with a potential ...


1

The term 'amplitude' is often used somewhat ambiguously. The most rigorous definition is that amplitude is simply $|A|$ (the modulus of $A$). In your case (unmodulated wave or oscillation) there's only one amplitude. But others count the number of peaks and troughs as 'amplitudes' like you are doing. You count only three but that's because Fig.14.2 only ...


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When you're in a moving vehicle and see trees or buildings, who is moving? Are you moving forward, or are the trees and buildings moving backward? Its counter-intuitive for beginners but both these views are absolutely correct. We can only describe the motion of an object from a reference frame. A reference frame is a specific configuration from where you ...



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