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Questions tagged [units]

Units are standards of measurement used for different types of quantities.

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What is the unit for work done?

My textbook's equation for work done is: work done = force * distance So this means that the unit should be Nm. However, when I researched on Google, a lot of people were saying that the unit is J....
74 views

Vector units with different unit in each component

I'm used to encounter units that come from product or division of units, such that $m/s$ or $kg\cdot m\cdot s^{-2}$. However, I have never seen a unit defined as a sum of units, for instance, $m+J$. I ...
57 views

A viscosity unit [closed]

Does the viscosity unit "$\mathrm{ps}$" exist or is it a misprint and refers to poise "$\mathrm{P}$"? Thank you A liquid of $0.014\,\mathrm{ps}$ viscosity and $1.4\,\mathrm{g/cm^3}$ density ...
170 views

Converting GPa and TPa to N/m

I have a problem with converting units, in some papers, ultimate tensile strength has been shown with GPa or TPa, but in some papers, it has been presented with N/m. (not newton per square meter) As ...
85 views

Why doesn't magnetomotive force have units of force?

Why does it have units of Ampere-turns and not Newtons? Is it a current, or turns mean metres?
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Angular Momentum calculation not adding up — Where is my error? [closed]

I'm recreating a calculation from this paper. The authors calculated the angular momentum (L) of a spinning disc with mass = 114.7 grams (0.1147 kg) and radius = 4.75 cm (0.0475 m). The disc spins at ...
93 views

How to check if a thing I have is exactly of 1 kg or not?

The definition of a kilogram is as far I know, Kilogram: The mass of a cylinder made of platinum-iridium alloy kept at International Bureau of Weights and Measures is defined as 1 kg. But it is ...
58 views

How bright is the night sky in $\frac{\mathrm{W}}{\mathrm{m}^2}$?

I'm looking at the Wikipedia page on sky brightness, which gives the answer in "S10" units. I've looked at the definition of S10 and I'm still completely at a loss as to how to convert that to SI ...
185 views

Why does $\frac{1}{4\pi}$ appear in many formulas? [duplicate]

Why do most of the physical equations have $\frac{1}{4\pi}$ as constants? I have seen that many equations have $\frac{1}{4\pi}$ as constants like Coulomb, pendulum problems, etc. Can anyone tell me ...
163 views

Reformulate quantum harmonic oscillator Schrödinger equation using dimensionless quantities

I am trying to rewrite a Schrödinger equation using dimensionless quantities but here, the potential is perturbed by $\lambda x^4$: \begin{equation}V(x) = \frac{m\omega^2}{2}x^2 + \lambda x^4\end{...
461 views

What unit of measurement is GV?

I am reading this paper; at page 12, it saids: Lockwood et al. (1986) found that the recovery time was independent of rigidity in the range ~ 2 to ~ 5 GV what is GV? I thought that rigidity was ...
83 views

How is the Length of a Meter Physically Measured

I have two parts to this question. First, I understand that the meter is defined as the distance light travels in 1/299,792,458 seconds. But how is this distance actually measured? The second is ...
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Give an interpretation of what $c=\frac{1}{\sqrt{\varepsilon_0\mu_0}}$ actually means

From my later school days on, the formula that impresses me the most is $$c=\frac{1}{\sqrt{\varepsilon_0\mu_0}}$$ I know how this can be derived, both from Maxwell Equations and more intuitively. I ...
3k views

What is a “decade” as a unit of measure (ex. a decade of the EM spectrum)?

Reading through papers and online sources about radio galaxies, I kept stumbling across a term--a "decade" of the electromagnetic spectrum. Radio galaxy emission encompasses "11 decades of the EM ...
134 views

The value of $c$ in $E=mc^2$

In Einstein’s formula $E = m c^2$, $c$ is the speed of light. However the speed of light is not a unique number. It can be expressed in kilometres per second or miles per second for example, which ...
797 views

Complete list of fundamental properties [closed]

What are all of the fundamental properties, that is all measurable quantities which are not derived from anything else? Many quantities are derived e.g. area is length squared, velocity is length per ...
84 views

Is energy always measured in units of mass × length$^2$/time$^2$ in physics?

Is it always $M\,L^2/T^2$? Is special relativity different from general relativity regarding the units of energy?
852 views

What unit of measurement is a BeV?

I am studying this paper by Gleeson and Axford from 1968. They often measure the energy of a particle in BeV: does it mean GeV, like a Billion of eV?
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How can distance and temperature be commensurable?

I am sorry to intrude. The discipline I know something about is metaphysics rather than physics itself. And on Stack Exchange I spend my time on English Language and Usage. I am struggling ...
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Dimensionality Dilemma: Dimensional Analysis Invalidates my Mathematical Model

I am trying to derive an equation that describes the rotational motion of an "auto-unravelling system": systems comprised of a material (string, chain, cloth etc.) wound around a cylinder and left to ...
294 views

What's the matter with Planck mass $M_P$ in Einstein-Hilbert action?

The Einstein-Hilbert (EH) action is often written as $$S_{EH}=\frac{c^4}{16\pi G}\int d^4x \sqrt{-g}R\tag{1}$$ and often as $$S_{EH}=\int d^4x \sqrt{-g}M_P^2 R\tag{2}.$$ Comparing (1) and (2), one ...
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Can units be plural? [duplicate]

I was in a conversation with my senior engineer where he kept on insisting that we can use plural when we write down any unit. I argued that it is not the 'common' practice or even throughout my whole ...
126 views

How to convert a quantity in natural units

Suppose I am working with a system of units where $c = G = \hbar = 1$. I can then write e.g. a distance in units of kg by converting with a factor of $$\frac{c^2}{G}$$ Now if I have an energy in ...
255 views

Why is $k$ taken as 1 in the derivation of $F=kma$? [duplicate]

In the derivation of F=ma, when we reach the point F=kma, we take k=1. Why can't we take 'k' as some other value?
87 views

What allows us to treat physical units in algebra?

I have been thinking about this problem: $$Speed = \frac{Distance}{Time}$$ Following this, is makes sense that the units of speed is m/s. However, I do not follow why we are able to divide units to ...
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Scaling atomic units with energy

In Hartree atomic units, $e = m_e = k_e = \hbar = 1$, and \begin{align} 1&\mbox{ a.u. of energy is }E=\frac{m_ee^4}{(4\pi\varepsilon_0 \hbar)^2}=27.21\mbox{ eV.} \\ 1&\mbox{ a.u. of time is }\...
I need get intensity of an LED light source, but I cannot convert lux to $W/M^2$ How does one convert illumination to irradiance? And what is the irradiance formula?