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

learn more… | top users | synonyms

0
votes
1answer
17 views

How could the BOE (barrel of oil equivalent) be measured?

The barrel of oil equivalent was given as an example of gigajoule scale energy. "The barrel of oil equivalent (BOE) is a unit of energy based on the approximate energy released by burning one barrel ...
-3
votes
2answers
30 views

Why can't we use Boltzmann's ideal gas law using temperature in Celsius (intuition)? [closed]

Mathematically, i can see why we won't get the same results when inserting a temperature in Celsius rather than Kelvin(because K=C+273.15), but i can't understand how can a law not "work" for any man ...
0
votes
1answer
34 views

Proving that Planck's Law is dimensionally homogeneous [closed]

I would like to know whether it is possible to show that Planck's Law is dimensionally homogeneous, as well as the steps taken to prove it. $$B_\lambda(\lambda, T) =\frac{2 hc^2}{\lambda^5}\frac{1}{ ...
1
vote
4answers
51 views

Same equation, different meanings

I went into a physics classroom today and saw this equation written on the board: $$ E = \frac \sigma \epsilon $$ At first I thought it referred to the electric field $ E $ between 2 parallel plates ...
-1
votes
2answers
55 views

Why is the mass of neutrino expressed in electronvolts?

The definition of electronvolt (eV) from wiki is In physics, the electronvolt (symbol eV; also written electron volt) is a unit of energy equal to approximately 160 zeptojoules (symbol zJ) or ...
1
vote
2answers
113 views

Is there an equivalent of the Planck length for time?

Is there an equivalent of the Planck length for time? I'd just like a term I may use (high-level) for a similar "unit of time"? I am not looking for a debate on how discrete time might be, but if ...
1
vote
2answers
63 views

Why are these equations valid despite seemingly inconsistent units?

I am having quite a difficult time in trying to understand what units are used in this paper and how to convert things to SI. For example, look at equation (1): $$T_M \approx 1500 \rho^{1/3}\ ...
7
votes
2answers
659 views

Can a half life be given in electron volts?

I'm using this link to search for particular energies in which gammas may be emitted (for nuclide identification on a gamma spectrum). If on the above link you go down to the "γ condition #1" line, ...
1
vote
0answers
96 views

Newton's Second Law of Motion

Newton originally wrote his second law as: "The rate of change of momentum of a body is directly proportional to the resultant force applied to the body, and is in the same direction as the force." ...
3
votes
3answers
74 views

Why are significant figure rules in Multiplication/Division different than in Addition/Subtraction?

I've never understood specifically why this is. Here's what I mean. In Addition/Subtraction, what matters are the digits after the decimal point. So for example: 1.689 + 4.3 = ...
0
votes
6answers
141 views

Dimension of an angle [closed]

Usually angles are described as dimensionless, justifying this by saying that they can be viewed as length divided by length. As a student of mathematics I'm asking myself wether this is a convention ...
0
votes
2answers
64 views

How are the SI units “generalised”?

How exactly are the SI units generalised from their definitions? E.g. the kilogram is a weight of an object of cylindrical form, with diameter and height of about 39 mm, and is made of an alloy of ...
1
vote
1answer
40 views

With radian as a unit, should action and angular momentum have the different units?

If one accepts radian as a fundamental unit, does it make sense that action and angular momentum have units differing in radian to the power of one? The same question applies for energy and torque. ...
4
votes
3answers
185 views

Why is the action dimensionless in natural units?

As I understand it, a natural system of units is one in which the numerical values of $c$ and $\hbar$ are unity, i.e. $c=\hbar =1$. What I find confusing is that they are still dimensionful, i.e. ...
1
vote
1answer
47 views

Pressure at ground level and at sea level

1atm = 101325pa 1bar = 100000 pa 1atm = 1.013 bar 1bar = 0.987atm From wiki: The bar is a metric (but not SI) unit of pressure exactly equal to 100000 Pa.[1] It is about equal to the atmospheric ...
3
votes
0answers
59 views

Why isn't $G=1$ as common as $c=\hbar=1$? [closed]

It is standard practice in theoretical physics to use a system of units in which $c=\hbar=1$. However, even though you could also set $G=1$, most physicists prefer not to. For example, in my cosmology ...
2
votes
3answers
87 views

What is the purpose of taking coefficients as 1 in numerical solutions?

How can we recover the real solution after getting a solution by solving with parameters set to 1? For example, on my case to solve the Shrödinger equation via finite difference method, the author ...
1
vote
1answer
61 views

Visualizing Physical Units in Phyiscs

I do best in physics when I can make sense of the units that accompany values, and I do this by visualizing in my mind what is happening. Take for instance, $v=\frac{s}{t}$. When I think of velocity I ...
0
votes
0answers
26 views

Units of Fourier Transform [duplicate]

I am a bit confused about the units of continuous time Fourier transform. Let's say that $x(t)$ is an input signal and has units of volts. Taking the Fourier transform of this yields $X(f)$. I would ...
1
vote
1answer
47 views

is Ù the same as omega as the unit of resistance?

I was making an exercise about DC motors and the resistance was given in Ù. Is this the same unit as Ω? Or is there a relation between these two units?
1
vote
5answers
112 views

What in nature causes Newton's gravitation constant to have it's given value?

Does the value of Newton's universal gravitational constant $G$ remain a mystery? Why does it have the value that it has?
1
vote
3answers
104 views

Power statement is valid for MW Or KiloWatts? [closed]

If I can talk to someone and tell him that a new power plant inaugurated by Prime Minister will produce $60$ megawatts per hour, will it be true to use $\mathrm{MW}$ unit for Power?
-1
votes
3answers
54 views

Why are measurements standardized the way they are?

Using meters as a base length, squaring or cubing lengths smaller than 0.67m makes the square term larger than the cubed term. This fact causes certain properties of physics (how rain needs to form?) ...
1
vote
1answer
37 views

Converting $W/m^2 $ unit [duplicate]

In my equation I have a unit measured in MET found here $1MET=58.2 W/m^2 $. But my other parameter which is metabolic heat generation is measured in $W/m^3$ . I want to convert $W/m^2$ units ...
0
votes
2answers
36 views

unit conversion issue

I have the following equation where $ T_0(x) $ measures the temperature in Celsius at point x. The parameter values are as follows. My question is how to handle the second term $Q_m \over ...
3
votes
1answer
87 views

Why does the vacuum permeability have the value of $\pi$ in it?

The vacuum permeability, or the capability of the vacuum to permit magnetic field lines, contains the value of $\pi$. Why? What does this have to do with the ratio of a circle's circumference to its ...
3
votes
2answers
109 views

Is it a problem that you can write the logarithm of a quantity with units? [duplicate]

While working out something in thermodynamics, I encountered an equation that had a term like $\log(n_1/n_2)$, where, $n_1$ and $n_2$ are the number densities. Now of course the argument of the $\log$ ...
0
votes
2answers
30 views

Dimensional equation for measuring logarithm of volume

I have a measure that uses radiation dose (M.U. $Gray$) and $\log(Volume)$. The measure is $[\frac{Dose}{\log(Volume)}]$ that is $[\frac{D}{\log(l^3)}]$ with $D$ as radiation dose (M.U. unit is Gray) ...
1
vote
0answers
29 views

Energy flux units [closed]

So I was looking at a calculation of energy flux: But the units don't make sense to me - how did the K go into the denominator at the end of the first line of working? Here's my working for the ...
1
vote
2answers
141 views

Can a quantity have two units?

We know that Force has unit of newton and torque has unit of newton meter. Then if you define the energy, which has same magnitude of work then, $W=Fx$ has unit of Joule ( $J$ ) (or $Nm$ ) while ...
0
votes
0answers
35 views

Does unit linear scale lead to linear scale of time?

I'm modeling movement of charged particles on computer using Coulomb's law and Newton's motion laws. As I try to simulate motion of small particles on small distances with small charges, I use my own ...
0
votes
1answer
44 views

Books or other sources for natural units, Planck units, dimensional analysis etc. for someone with only high-school physics knowledge

I'd like to know more about natural units, Planck units, dimensional analysis, etc., and things like how units are "created" by man or by the universe, universal constants and where they come from. ...
0
votes
1answer
49 views

Educational benefit of putting units outside of variables? [closed]

When I studied physics (both in high-school and university), in all of the worked examples, variables would be used to denote physical quantities, and thus include dimensional units. For example, ...
0
votes
1answer
39 views

How do Hubble Units work?

I'm reading through a document - Briel et al (1992) (pdf) - and I've come across Hubble units with which I'm not familiar. How do you interpret something like $$h^{1/2}_{50} \:\mathrm{cm}^{-3}$$ or ...
0
votes
1answer
47 views

Units of Velocity Components and Metric Tensor Components

I was watching a GR lecture on youtube, and the speaker explains that the units of the components of velocity are $[v^{\alpha}]=\frac{1}{T}$, the metric tensor has units $[g_{\alpha\beta}]=L^2$, and ...
0
votes
1answer
45 views

Definition of unit of force [closed]

As we know $1\ \mathrm{N}$ is the force which can accelerate $1\ \mathrm{kg}$ mass with $1\ \mathrm{m/s^2}$ acceleration. But for which surface is this definition given? I mean a $1\ \mathrm{kg}$ ...
-1
votes
2answers
81 views

cm^-1 and ns^-1 relationship

In my last Phys.SE question Emilio Pisanty mentioned this relationship $1 cm^{-1} = 10^n c^{-1} ns^{-1}$. I was wondering where this relationship came from. Does anybody know? Second of all, I am not ...
-4
votes
0answers
50 views

How to compare dimension of this with velocity [closed]

Prove that the dimensions of $\large \sqrt{\frac{1}{με}}$ are that of the velocity?
1
vote
2answers
76 views

System of Units where Coulomb's constant $k_e = 1$?

I am reading (and trying to replicate the results of) a paper in the field of condensed matter physics. The system consists of a spatially separated electron and hole whose Coulomb interaction is the ...
2
votes
2answers
50 views

Why does physical quantity misinterpretation result in near-identical torque results?

I am going to use an equation $$\text{torque} = \frac{\text{power}\times 5252}{\text{RPM}}$$ derived on Wikipedia. Suppose that $\text{power} = 100\ \mathrm{hp}$ and $\text{RPM} = 5252\ \mathrm{rpm}$ ...
0
votes
2answers
82 views

How the standard units for length force and time are defined in US Customary Units as standard units are defined in SI?

I'm much confused about US customary units so I want to ask a lot more questions under single question.First how standard units ,in US customary Units,of force time and length are defined as second or ...
1
vote
2answers
65 views

Units of the derivative of a function

I have a function $\phi(\mu, \sigma)$. $\mu$ and $\sigma$ are voltages (in mV in my case), so $\phi$ is a function of two voltages. $\phi$ itself, however, is in units of time (ms in my case). ...
0
votes
0answers
60 views

How do I convert pressure and flow from Imperial to metric units?

I'm not a physicist or have much experience in engineering. However, for a programming task, I need to change code that calculates "pressure, head, feet of fluid, gauge" into "meters of head, ...
0
votes
2answers
61 views

What defines a unit system and how many constants can we set to 1?

Is it possible to have a system of units in which both $\frac{1}{4\pi\epsilon_0}$ and $c$ equal 1?
4
votes
4answers
2k views

What happens to the units when squaring a variable?

What happens to the units of a squared variable? For example, if I squared velocity, would the units, metres per second (${\rm m}/{\rm s}$), change as well?
1
vote
0answers
44 views

Units of angular power spectrum

I am not sure whether this question might be better suited for crossvalidated or stackoverflow, but I will give it a try here: I have a map of the full sky in in the healpix format, units are $\rm ...
3
votes
1answer
79 views

Definition of Sievert (Sv) unit - is it whole body mass?

I'm wondering about the definition of the Sievert (Sv) unit. It is J/Kg but is that Kg the mass of the whole body or just of the exposed body part? For instance, when a table says that an x-ray of a ...
1
vote
1answer
223 views

conversion of units

I have a quantity that I need to convert to different units. First, I need to note that the value is in the natural units system. The quantity is in cm^-1 (or, to be accurate, $cm^{-1}\hbar c /k$, ...
1
vote
0answers
68 views

What unit system puts a bunch of powers of ten in Maxwell's equations?

In what unit system can we get the Maxwell equation in the following form (section 1.2 from Lewin's book Advanced Theory of Waveguide) $$\nabla\times \vec E = -10^8\mu \frac{\partial \vec H} ...
3
votes
0answers
218 views

When can two quantities be added together?

Whenever two things are to be added together, one typically needs to check whether this actually makes sense, and an addition is said to make sense, in principle, when the units match up. Yet, ...