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

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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 ...
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58 views

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 ...
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36 views

Why does the angular speed formula end up in radians per second?

So, in my homework I am given the radius and also the tangential speed $v$, the measurement for radius is meters; the measurement for $v$ is $m/s$. I don't understand how by after calculating the RPM ...
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33 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) ...
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110 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 ...
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73 views

Convert cubic feet per sec to feet per sec

Is there a way to convert cubic feet per sec to feet per sec. Or in general volumetric flow to velocity? I want to know the time taken by water to travel from point A to point B. I have the distance ...
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95 views

Is meters per second equivalent to seconds per meter?

I know this question is probably ridiculous, but bear with me for a moment. This thought emerged while I was converting between nm and wave numbers ($\rm cm^{-1}$). In order to prove this conversion, ...
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327 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, ...
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102 views

Experimentally finding units of physical quantity?

Say you had a new physical quantity you wanted to determine the units for. How do you go about this? For the strength of an electromagnet for example, you could carry out a simple experiment like the ...
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58 views

What is the difference between emu and esu?

Ok...so this is the statement given in my book: a) In C.G.S System the unit of charge is electrostatic unit of charge (E.S.U). It is also called Stat Coulomb (StatC). b) In C.G.S system, the unit ...
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67 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 ...
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25 views

why this formula has answer in micrometer

Formula e=0.8+0.06(m+0.25√d) e=pitch error in microns m=module in mm d= pitch circle diameter in mm From school we have learned that if we put value of terms like m and d (terms from above example) ...
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48 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. ...
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29 views

Can I describe resistance without using an Ohm?

Can resistance be described with units $\rm cm^2/sec$? If so, how would this (resistance) relate to permeability?
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27 views

Recalculating lux from EV

I have to calculate amount of light from IR emmiter. The only equipement, that I can use is Sekonic Light Meter like this one: http://www.ebay.com/bhp/sekonic-l-358 The problem is that i need to have ...
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107 views

Is there a way to convert CFM (rate of air moved) to kilograms of lift generated?

Is there a way to convert CFM as in a rate of volume of air moved to kilograms of lift generated?
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85 views

Using the boltzmann equation to find neutrino decoupling temperature

I'm an undergraduate student currently following a particle astrophysics lecture. I was reading some stuff about the neutrinos decoupling before the $e^+ e^-$ annihilations. It's possible to quickly ...
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50 views

Units and missing constants in quintessence expressions?

In cosmology, quintessence is an alternative to the cosmological constant. In this approach (described here), we consider a scalar field $\phi$ and its self-interacting potential $V\left(\phi\right)$ ...
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What is the constant appearing in the low energy action?

Usually one finds this expression for the low energy action $$S = \frac{1}{2\kappa_0^2}\int d^D X\; \sqrt{-G}\; \mathrm{e}^{-2\Phi}\,(R-\frac{1}{12}H_{\mu\nu\lambda}H^{\mu\nu\lambda}+4 ...
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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." ...
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59 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 ...
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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} ...
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77 views

Black Hole Entropy Calculation

I was watching "Leonard Susskind on The World As Hologram" ( youtube ). At one point he describes the way Bekenstein calculates the entropy of a black hole. Paraphrasing: Take a minimally sized black ...
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Which physical entities equal “distance times time”?

Are there useful physical quantities with dimensions of distance-time? The background for this question is a differential equation which I try to make sense of: ...
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How to understand/derive Eq 5.5 in Geiner's Quantum Mechanics - An Introduction?

Geiner's Quantum Mechanics - An Introduction has an unnumbered equation above Eq. 6 in section 2.4 discussing density -- not sure if it is energy density -- of radiation: ... $$dE/dV = E/V =a ...
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Do doomsday arguments influence doomsday hypotheses?

The doomsday argument supposes that in the absence of any other knowledge, if we know the age of something now, we may assume that we are seeing it in the middle of its lifetime and then calculate our ...
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209 views

Scale-invariant differential operator

For example, the differential operator Laplacian is $$\nabla^2 = \frac{\partial^2}{\partial x^2}+\frac{\partial^2}{\partial y^2}.$$ My questions are: Is it scale-invariant? what is ...
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37 views

Photon Propagator in QFT

Please forgive my temporary split-brain, but I'm a little thrown off by something when considering units at the moment. In QED (depending on the guage), the photon propogator is written as ...
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39 views

Is there a 3D analogue of angle?

A one-dimensional angle is a wedge, almost like a slice of pizza. A two-dimensional angle is an angle squared, like the cone of light produced by a flashlight. This is called a solid angle. Is ...
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50 views

What kind of unit is $m^2s^{-4}$ in terms of gyro/accel?

Background While working on something in the field of avionics, I have discovered the following unit as part of an inertial-physics equation... $$m^2s^{-4}$$ I am trying to figure out the formal ...
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37 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 ...
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87 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, ...
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65 views

Terminology: Gauge stress?

When a material is loaded with a force, the stress at some location in the material is defined as the applied force per unit of cross-sectional area. If I have a material submerged in pressurized ...
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47 views

Heavyside Lorentz units and Gaussian units

What is the relation between Heavyside Lorentz units and Gaussian units? From this Wikipedia article, I noticed there are $4\pi$ difference between them, but my TA wants more. Is there other ...
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103 views

What is the meaning of $G/cm^2$?

I'll prefix this question by stating that I am not a physicist, I am a programmer. I am working on updating a (very old) program that calculates the performance of a magnet. This whole program is in ...
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134 views

cgs Gauss' system of units

I had never seen this system until today, and I'm really confused. I've read the wikipedia article about it but I still don't know how to change between this and the international system. For example, ...
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369 views

I'm having trouble understanding the dimensions of this falling body problem

I'm working with this: A 50 kg mass is shot from a cannon straight up with an initial velocity of 10m/s off a bridge that is 100 meters above the ground. If air resistance is given by 5v ...