# Tag Info

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An example that comes from comptom scattering would be something like $m_e c/\lambda$ that appears during the calculation because $1/\lambda$ is related to the momentum of the photon. By itself this quantity is not usefull, but it does appear during the calcuations

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Two examples of the product of mass and duration being quantified over vastly different ranges: 1) It is not entirely uncommon to cost a truck on a tonne.hr basis. Here the payload is measured in tonnes and the trip duration in hours. The example given is: "if a truck hauls 35 Tonnes and the trip time is 4 hours, the number of tonne.hours is 140 (35 x ...

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There's nothing too common or universal, especially in basic kinetics, and moreover this shouldn't be much of a surprise. There are infinitely many unit combinations one can construct, and there are only finitely many combinations we bother to give special names to, so necessarily some combinations will not have special names. You might object that maybe at ...

2

This is a question of units, and I am not going to pretend I present an answer which would be anyhow natural from the point of view of classical non-relativistic physics. But consider the following. We have a version of the Heisenberg uncertainty principle $$\Delta E \Delta t \geq \frac{\hbar}{2}$$ This for example tells us that an excited state with a ...

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I don't know if I'm right, but here is an attempt to estimate one effect that might be relevant. If a 133Cs atom of mass $m$ is in thermal equilibrium with blackbody radiation at temperature $T$, then it has an average kinetic energy $(1/2)mv^2=(3/2)kT$. This will cause Doppler shifts. The longitudinal Doppler shift cancels out on the average, but the ...

3

How a unit is chosen to be defined depends in large part on how precisely the unit can be reproduced based on that definition. Two different atomic clocks built using the best currently possible methods will produce almost exactly the same answer for how long a second is, to within about 1 part in $10^{14}$. The second is defined in terms of a property of ...

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kilogram-seconds is the unit of momentum in a technical system. kilogram = force, second = time force * time = momentum. The sort of range i have found for the theoretical scale is density^(0,1) * velocity^(0-3) * length ^ (0-5) covers nearly everything.

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Here is an example: assume that you have a wave that can lift a weight (such as ultrasound), and that it obeys a law in which the mass that can be lifted is proportional to the frequency. Then: M=C*f where C is a constant. The units of C are kg/Hz=Kg.s. The example is not as artificial as you think, because C plays a similar role than a resistance in ...

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