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

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Why is metre defined in terms of distance covered by light in 1 second? [duplicate]

Why is the unit of length defined with the help of unit of time? (1m=x covered by time in 1/3*10^8 s) Isn't length a fundamental unit too, why is it defined in terms of an other unit?
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What is the significance of Planck force?

I have been curious to find what could be the significance of Planck force? It is calculated by the formula $c^4/G = 1.21031359\times 10^{44} \, \mathrm{N}$, where $c$ is the speed of light and $G$ is ...
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What would be the standard for the unit of pressure Pa or MPa?

Me and my friend are doing a project and in our result we shall provide a plot, and on our axes we are going to write out the units. My friend wrote "xx MPa", claiming it was standard in reports to ...
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How can geometrized units have more than one constant equal to 1?

I can understand how you could manipulate units to make a certain constant equal to $1$, like $c$ or $G$, et cetera. But how can you make it so two constants (in this case $c$ and $G$) are equal to ...
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When can the constant of proportionality in an eq be set equal to 1 and when not? [duplicate]

In $F=kma$, $k=1$ but in $F=kx$, $k$ is not equal to 1?So what are the conditions for the constant of proportionality to be set 1?
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What is the dimensional formula of angular velocity?

I have problem to determine the dimensional formula of angular velocity. My friend said that the dimensional formula of angular velocity is $T^{-1}$. It's come from rad/s, rad is dimensionless, the ...
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Unit of gradient/slope?

So I have a graph: The value of the gradient/slope is $1.6±0.4$ and the value of the intercept is $0.9±0.4$. But what are the units of the graph? Is the unit of the gradient $v^2M^{-1}$? What about ...
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Differences in notation of momentum 4 vector

I have noticed three ways to write the 4 momentum vectors: $P = (E/c, \vec{p})$ $P = (E, \vec{p})$ $P = (E, c\vec{p})$ I know how to derive equation 1, and as far as I know, one can use the ...
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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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13answers
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Are units of angle really dimensionless?

I know mathematically the answer to this question is yes, and it's very obvious to see that the dimensions of a ratio cancel out, leaving behind a mathematically dimensionless quantity. However, I've ...
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In this energy conservation problem, why are the answers different with different units? [closed]

Really basic question, but basically I'm given a change in height in centimeters (that's how I measured it). From that, I'm supposed to find the initial kinetic energy. $KE_i = PE_f$ After doing ...
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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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How do Calories (kcal) relate to watts?

In thinking about exercise and "burning calories" it occurred to me that there should be some fairly intuitive correlation between the biological energy conversion going on in a person's body with the ...
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1answer
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Is there a software to convert units for quantities and equations? [closed]

For example, Often I end up with a complicated equation that uses non-standard units. In these equations, Temperature is in eV and Magnetic field is in Gauss. I need to convert my equation to another ...
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The Kelvin-Celsius problem

Let's suppose we have temperatures 30°C and 35°C. Converting them to Kelvin we have 303.15K and 308.15K. In the second case, the temperature difference is 5K. While in first case, temperature ...
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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 = ...
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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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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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1answer
47 views

Fine structure constant and unit conversion [closed]

In a paper I'm reading, the author writes down the following formula: $$\Gamma=\dfrac{\alpha^2}{576\pi^3}\dfrac{\left(4+z\right)^2}{z}\dfrac{m^5}{m^2_\pi f_\pi^2}$$ $\Gamma$ is a function of $m$ (in ...
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What are the units pm/K?

I can only think of picometres, but it doesn't seem to make sense. Here is the context, from the paper 'Towards Reproducible Ring Resonator Based Temperature Sensors', Klimov et al., Sensors & ...
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Do all equations have identical units on the left- and right-hand sides?

Do all equations have $$\text{left hand side unit} = \text{right hand side unit}$$ for example, $$\text{velocity (m/s)} = \text{distance (m) / time (s)},$$ or is there an equation that has different ...
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Arguing on dimensions of logarithms and exponentials [duplicate]

Suppose you have some physical quantity $x$ of dimension $l$. We all know that the dimension of $x^2$, for example, will be $l^2$, and that of $\dfrac{1}{x}$ is $l^{-1}$. However, what will be the ...
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129 views

Difference between theoretical equations and empirical equations

Some equations are theoretical in the sense that they are derived from an underlying theory. Other equations are empirical in the sense that they were selected only because they fit experimental data ...
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how do we actually count the number of magnetic field lines and what does the gap between those lines describe?

on the internet,(http://nuclearpowertraining.tpub.com/h1011v1/css/h1011v1_53.htm), there is a statment which says that 1 Wb is $1\times 10^{8}$ magnetic field lines. My question is, How do we count ...
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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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Why do we need constants? [closed]

This question is driving me crazy because I cannot find a straightforward answer. I want to know what a physical constant exactly is. I know that it’s a value that doesn’t change, but what is it? Why ...
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1answer
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How to read this length interval in imperial units?

I am from Europe and I do some research for my thesis. I found this picture, which is very usefull for me, but unfortunately the lengths are in imperial units (for lenght they are using something like ...
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156 views

Why did Einstein took speed of light unit or constant in his equation of relativity?

We can find that no object can have speed more than light from Einstein's equation of relativity because if anything have speed more than light then we get -ve value within square root. But why did ...
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Classification of plane angle as fundamental or derived

I recently started with my high school studies and the chapter I am stuck at is units and measurements. I was told about two types of physical quantities and my teacher gave me the following ...
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How to interpret the units of the dot or cross product of two vectors?

Suppose I have two vectors $a=\left(1,2,3\right)$ and $b=\left(4,5,6\right)$, both in meters. If I take their dot product with the algebraic definition, I get this: $$a \cdot b = 1\mathrm m \cdot ...
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Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?

In classical physics we often cast an analogy between translational and rotational systems Force < > Torque Energy < > Rotational Energy Momentum < > Angular Momentum and considering SI ...
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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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How does the Fourier Transform invert units?

I don't really understand how units work under operations like derivation and integration. In particular, I am interested in understanding how the Fourier transform gives inverse units (i.e. time ...
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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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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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How units were defined?

I was wondering how we humans can be sure that one meter is one meter and that one second is one second. Nowadays, except for the Kilogram, all other units are well defined using highly accurate ...
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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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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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What in nature causes Newton's gravitation constant to have its given value?

Does the value of Newton's universal gravitational constant $G$ remain a mystery? Why does it have the value that it has?
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Units don't match in the torsional spring energy!

According to Wikipedia's description of torsion springs and according to my understanding of physics the energy of a torsional spring can be written as $$U=\frac{1}{2}k \varphi^2$$ where $k$ is a ...
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Does the imperial system have any advantages (besides its wide acceptance in the US)? [closed]

The United States (and one other country, somewhere in Africa I think) uses the imperial system (feet, pounds, etc.), while pretty much everyone else uses the metric system (meters, kilograms). The ...
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What is the fundamental units for coulomb? [closed]

Everything I saw suggests coulomb has no fundamental units. So then how is Newton/Coulomb equivalent to Volt/meter?
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Definition of atmosphere unit and relation to temperature and gravity

I've seem sometimes the atmosphere unit for pressure be defined so that $1\ \mathrm{atm}$ would be the mean atmospheric pressure at sea level. I've seem on the other hand the following definition: ...
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What does the $k_e$ in Coulomb's law and $G$ in Newton's Universal Gravitation Law mean?

I very well understand the proportionality relation that was used to derive these laws like $F$ is proportional to product of masses and inversely to radius squared and hence its proportional to the ...
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Which was the first Coulomb's constant value? [closed]

Which was the first Coulomb's constant value? I didn't found any info in the Internet. I need the first value of K to compare it with my experiment. Could you please help me?
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What is “unity constant form” and why is it useful?

I read the following in a tutorial: The standard transfer function of a first order system is: $$G(s) = \frac{k}{s + a}$$ Arranging this into unity constant form gives: $$G(s) = ...
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Torque wrench units

My torque wrench has these markings on it: (da. Nm.) and on the line below M. KGS. I can tell from comparing the scale to poundf-foot on the other side that the scale units are kilograms-meter ...
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Dimensions of physical quantities in quantum mechanics

In most introductory quantum mechanics classes, we are introduced to the Dirac notation, concept of the 'state' of the system being represented as an abstract vector in the Hilbert space associated ...
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69 views

Is the unit symbol written twice when using the +\- symbol?

When notating error using the $\pm$ symbol, are the units only ever included at the end? For example: 10.2 $\pm$ 3.2 m rather than 10.2 m $\pm$ 3.2 m This seems to be correct though I ...
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Square bracket notation for dimensions and units: usage and conventions

One of the most useful tools in dimensional analysis is the use of square brackets around some physical quantity $q$ to denote its dimension as $$[q].$$ However, the precise meaning of this symbol ...