Questions tagged [si-units]
A set of internationally accepted units to aid in communication of measurements.
662 questions
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Why is it watt second instead of watt per second? [closed]
We say 1 meter per second to express 1 meter covered in 1 second. Why can't we say 1 watt per second when 1 watt is used in 1 sec?
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How we assigned a charge to everything after defining the charge of electron?
One ampere corresponds to the flow of approximately $6.241 509 074 × 10^{18}$ elementary charges passing a cross-sectional area in one second as per the 2019 revision of SI, fixing the elementary ...
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What kind of mathematical objects are units of measurement?
Multiplication and division of units of measurement seems to be defined, e.g., $\mathrm{N}\times\mathrm{m}=\mathrm{N}\text{-}\mathrm{m}$, m/s = m/s (a rather unsatisfactory example---help).
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What is the tension for a cosmic string formed at the electroweak scale?
Cosmic strings are characterized by their dimensionless tension, $G\mu$. Their mass per unit length $\mu$ is given by the square of the energy scale of their formation. For strings formed at the ...
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Can the unit of Kelvin be defined as an accelerating charge?
I stumbled upon this list of Planck units; what surprised me was how temperature could be defined as Acceleration*Charge/2π.
gp = Planck acceleration, e = elementary charge
This derivation would ...
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Website/code for finding base SI for a quantity [closed]
I often find myself wanting to know the dimensions of large-ish expressions. Something like $\frac{e^2}{4\pi m \omega^2 \epsilon_0}$ say. I know I can evaluate this by hand, but I'd really enjoy some ...
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Very elementary question - would this work as a primitve definition of mass?
I have recently been thinking a lot about foundational quantities in physics and chemistry (I study chemistry as an undergraduate), and how to define them.
It seems quite easy to define at least time ...
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CGS unit of charge in dimensional analysis
For converting a $\text{Newton}$ into a $\text{Dyne}$, we can simply use $nu = \text{constant}$ where $n$ is the magnitude and $u$ is the unit.
A similiar method can be used to convert all SI units ...
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Why are there no universal constants associated with candela?
I'll start by saying that I'm more oriented towards the math community and I hope to write a good question.
Context
I'm taking a quantum mechanics course where the professor is using a convention ...
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What are the units of mass flux?
I see 'mass flux' and 'mass flow rate' both used for the same system (ex: Mass flux across a volume).
From various sources it seems like 'mass flux' should have SI units $\mathrm{kg \times s^{-1}\...
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Why is the permeability of free space $\mu_0$ equal to $4\pi*10^{-7}\mathrm{\frac{N}{A^2}}$?
I understand why we might expect to see a $4\pi$ in $\mu_0$, given that we see relationships between geometry and natural phenomena, like with Gauss's law giving us $k_e = \frac{1}{4\pi\varepsilon_0}$ ...
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$\beta$ and $T$ in thermal field theory
I've learned in statistical mechanics that $\beta = \frac{1}{kT}$, which, in natural units, simplifies to $\beta = \frac{1}{T}$. When I started studying thermal field theory, it seemed that this ...
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Why is acceleration's formula's denominator squared?
If I accelerate by 10 meters per second, that means that I am accelerating by 20 meters per 2 seconds.
Plug this into the currently accepted formula:
20 meters / 2 seconds squared. So that means I am ...
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A question about units conversion
I’m somehow confused about the units conversion for some quantity, so any help is much appreciated. Suppose:
$
\rho = k^2 H^2 t^2,
$
where $k^2 $ and $t^2 $ are variables, $k$ is in unit Hz and $t$ is ...
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Question about both sides of the Einstein field equations
If both sides of the Einstein field equations need to have the same measurement units, how can the coefficient of the energy momentum tensor convert all of the units of the energy momentum tensor (...
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