# Tagged Questions

Dimensional analysis means to obtain results by analyzing the units in question, etc. DO NOT USE THIS TAG if your question is about degrees of freedom or spatial dimensions.

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### Why is $(4.9v*t^2)/4$ equivalent to $1.225v*t^2$? [on hold]

In this khan academy video: https://www.khanacademy.org/science/physics/one-dimensional-motion/kinematic-formulas/v/deriving-max-projectile-displacement-given-time At 6:58 he derives the second ...
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### Why are radians more natural than any other angle unit?

I'm convinced that radians are, at the very least, the most convenient unit for angles in mathematics and physics. In addition to this I suspect that they are the most fundamentally natural unit for ...
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### Are there physical law that are not unit-free?

One of the prerequisites of the Buckingham Ï€ theorem is that the physical law in question should be unit-free. I couldn't find an example of a physical law that is not unit-free. Is there such thing? ...
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### Is the concept of work only defined in mechanics?

I'm studying energy and work, so far it looks like work only makes sense in kinematics (objects that move), but energy makes sense in many other ways (electric, thermodynamic, mechanic). Is work a ...
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### How to identify the sign of a derived nondimensional parameter and its physical meaning?

I think that the nondimensional group is ordinarily defined to be positive value in a physical problem. But in some particular case, we probably need to decide the sign of a derived dimensionless ...
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### How can geometrized units have more than one constant equal to 1?

I can understand how you could manipulate units to make a certain constant equal to $1$, like $c$ or $G$, et cetera. But how can you make it so two constants (in this case $c$ and $G$) are equal to $1$...
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### When can the constant of proportionality in an eq be set equal to 1 and when not? [duplicate]

In $F=kma$, $k=1$ but in $F=kx$, $k$ is not equal to 1?So what are the conditions for the constant of proportionality to be set 1?
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### What is the dimensional formula of angular velocity?

I have problem to determine the dimensional formula of angular velocity. My friend said that the dimensional formula of angular velocity is $T^{-1}$. It's come from rad/s, rad is dimensionless, the ...
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### What does it mean to take a derivative with respect to $\hbar$?

Problem 6.32 of Griffiths Introduction to Quantum Mechanics, 2ed is In part (b), we take a derivative with respect to $\hbar$. Since $\hbar$ is a constant, what does it mean to take a derivative ...
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So I have a graph: The value of the gradient/slope is $1.6Â±0.4$ and the value of the intercept is $0.9Â±0.4$. But what are the units of the graph? Is the unit of the gradient $v^2M^{-1}$? What about ...
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### Differences in notation of momentum 4 vector

I have noticed three ways to write the 4 momentum vectors: $P = (E/c, \vec{p})$ $P = (E, \vec{p})$ $P = (E, c\vec{p})$ I know how to derive equation 1, and as far as I know, one can use the ...
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### Issues of normalization & differential final state momenta in analysis of normalized differential quantum-field-theoretic probability of scattering

The normalized differential quantum-field-theoretic probability $dP$ of scattering is given by $$dP=\frac{|\langle f |S|i\rangle|^{2}}{\langle f|f\rangle\langle i|i\rangle}d\Pi,$$ where $|i\rangle$ ...
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### Proper units for physical quantities when $\hbar$=$1$

How to deal with the units of quantities if $\hbar=\tfrac{h}{2\pi}=1$? For example, the energy $E=\hbar\omega$: If I have chosen $\hbar=1$, how do I use the units to properly differentiate between ...