# Questions tagged [units]

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

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### Do the units of $G/c^4$ make intuitive sense?

In classical Newtonian mechanics, gravity is explained by: $$F=G \frac {Mm} {r^2}$$ Where $F$ is the force due to gravitation, $M$ and $m$ are the masses of the two bodies in question, $r$ is the ...
6answers
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### Why is it “bad taste” to have a dimensional quantity in the argument of a logarithm or exponential function?

I've been told it is never seen in physics, and "bad taste" to have it in cases of being the argument of a logarithmic function or the function raised to $e$. I can't seem to understand why, although ...
1answer
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4answers
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### How many Newtons are in a kg exactly?

I understand that it is supposed to equal the gravity coefficient, which is defined as exactly 9.80665. But when i search google i saw one result saying 9.80665002864, and at first i thought it may ...
2answers
546 views

### Gravity acceleration - why is it inverse time squared?

I've looked up and understand the reason behind the number of the acceleration of gravity $(9.8)$. But whenever people describe it they say it's $9.8 \text{m/s}^2$. I don't understand why it's ...
1answer
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### Units of a vision [closed]

I have a basic question about physical units. Say I have the following value: a= $\frac{m1}{m2·g}$ m1,m2 being masses and g being gravitational acceleration. What would the units of this value be? ...
1answer
857 views

### What's the conversion between apparent magnitude and lux?

I know the apparent magnitude of the sun, but I'd like the units in lux. Please also direct me to a reliable source if possible.
0answers
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### Metre Definition from speed of light [duplicate]

Why is 1 metre defined as the distance travelled by light in 1/299792458 seconds rather than 1/300000000 seconds?
4answers
216 views

### Representing dimensions in Dirac delta function results

The Dirac delta function can be defined as $$\delta(x)=\frac{1}{2\pi}\int_{-\infty}^\infty e^{itx}dt$$ From this we see that the dirac function has units of $x^{-1}$. How do we represent the units ...
1answer
385 views

### How to understand the units of Dispersion Measure?

In astrophysics and pulsar astronomy, a typical quantity is the dispersion measure or DM, which is the integral of the electron number density along the line of sight, $$DM = \int_0^d n \, dl$$ up ...
1answer
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### Can Amps be used as a unit of measure for the amplitude of an EM wave?

As far as I know the definition for the amplitude of a wave is the distance between the line $y=0$ and the peak of the wave which in most cases is going to be a unit of length. I also understand that ...
1answer
68 views

### Why does this paper report potential energy in kHz, and what does it mean?

I am interested in studying theoretically the double well system shown in the figure below, which shows an experimental demonstration of an atomtronic battery. Caption: Figure 1. (a) ...
4answers
662 views

### How to express an energy in natural units

If I have some angular frequency e.g. $\omega [\text{rad } \text{s}^{-1}]$, I can easily express this as an energy as $E = \hbar \omega [\text{ J}]$. Now suppose I am working in Natural (Planck) ...
1answer
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### Dimensions of charge in natural units

The natural units $$G = c = \hbar = k_{B} = 1$$ set fundamental constants of gravity, relativity, quantum physics, and statistical physics to simple numbers. However, surprisingly, the natural ...
2answers
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### Optimization problem and measurements

This is more of math problem, but my doubt is about the measurement units of the final answer so I figured I'd post it here. Problem: A lighthouse is located on a small island 3 km away from a ...
1answer
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### d'Alembertian inconsistency

I'm reading The Feynman Lectures on Physics, Volume II, Chapter 25. I'm confused as to why the d'Alembertian is defined in there as follows (Page 25-7, Eq 25.20):  \Box^2 = \frac{\partial^2}{\...
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### Dimensional analysis problem

I am asking this question here because i think this is fundamentally linked to physics as it revolves around around dimensional analysis and physical quantities. Background: Amount of substance is a ...
1answer
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### Imperial to Metric lenght [closed]

I'm from Metric based country and have an unusual for me imperial notation. Google didn't clear that up for me so I'm asking it here: I have a wall with measures: 10'7-1/4'' What's 7 ? is it tenth of ...
1answer
660 views

### Calculating the unified atomic mass unit [duplicate]

The masses of electron, proton and neutron (in SI units) are (approx.): \begin{equation} m_e=\text{electron mass}=9.109\times 10^{-31}\ \text{kg} \end{equation} \begin{equation} m_p=\text{proton mass}...