Questions tagged [units]

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

Filter by
Sorted by
Tagged with
-1
votes
1answer
18 views

Error Analysis - Units and Dimensions [closed]

I have a question regarding error analysis in Units and dimensions chapter in physics. It is regarding finding equivalent resistance in parallel I have a attached 2 images of the same question solved ...
-2
votes
1answer
40 views

If a model car is made of 9.35 kg iron, what is the mass of gold required to recast the car using gold? [closed]

The detailed question is An automobile company displays a die-cast model of its first car, made from 9.35 kg of iron. To celebrate its hundredth year in business, a worker will recast the model in ...
0
votes
0answers
17 views

Cgs to Si with Force

So i just have a Problem with the transition from Cgs to SI. I want to Calculate the Force of the Plates of a Capacitor. The Formula is the following:(k=1,2,3 and Einstein Notation is used and T is ...
0
votes
1answer
35 views

Making the distinction between position and time in a gravitational system

Say we have a large spherical shell of thickness $R$ floating in space. The shell has a hole of negligible radius punched into one side that allows for a ball of mass $m$ to pass through. Say now that ...
1
vote
1answer
40 views

Why do we need to convert revolutions into radians before we multiply with meters?

When we are calculating tangential acceleration, I notice that we have to convert the $\alpha$ that was in unit of rev/min^2 into the unit of rad/min^2 before we are able to multiply this value with a ...
1
vote
4answers
80 views

Basic Question About Canceling Units

This is a very basic question but, here it is. In a given equation, where I have a term such as 4 m/s and I multiply this by the variable t, which is time, why is it incorrect for me to cancel out t ...
0
votes
1answer
51 views

Boltzmann constant in atomic units

I was just wondering what value the Boltzmann constant $k_B$ takes when we are using Hartree atomic units (i.e $\hbar=e=a_0=m_e=1$) where the unit of energy is 1 hartree. Should we we convert $1.38 \...
0
votes
1answer
25 views

Subatomic natural units

In High Energy Physics it seems to be common use to measure everything in terms of eV powers, by assuming $\hbar = c = 1$ (dimensionless). Often times this system of units is referred as Planck units, ...
-1
votes
1answer
35 views

Converting light-year to $m\cdot y/s$

For the solution to question $a$ of this problem, I'm confused with what that $3.0\times 10^8 m/s$ conversion factor is. I thought that light year is a measurement of distance, so why are we ...
2
votes
1answer
54 views

SVD of $2\times 2$ matrix where entries have different units

I have the following matrix: $$ M = \begin{pmatrix} 1 + xy & y \\ x & 1 \end{pmatrix} $$ where $x$ has the unit $m^{-1}$ (per meter) and $y$ has the unit $m$ (meter). This matrix acts on real ...
-3
votes
2answers
96 views

Negative Celsius Temperature [closed]

If the Celsius scale is from 0 (freezing point) to a 100 (boiling point) then how is it that we can have negative numbers like -3 degrees Celsius? And can we also have temperatures like 120 degrees ...
2
votes
1answer
53 views

Units of Dirac delta potential constant

Suppose we have a Dirac delta potential correction of the form $$ V(x)=V_0\delta(x-x_0)$$ What would be the units of $V_0$ ? I think it should be units of energy as calculating first order ...
1
vote
1answer
54 views

Why plane and solid angles have units?

I have learnt that the dimensionless quantities have no unit. Such as the refractive index have no unit. But plane angles and solid angles have their radian and steradian units, although they are ...
0
votes
0answers
29 views

Natural units in Monte Carlo simulations

I'm wondering how, if one sets the Boltzmann constant $k_B=1$ in an MCMC simulation used to sample the Boltzmann distribution $P(x,p) \propto \exp\left(- \frac{\frac{p^2}{2m}+\frac{1}{2}m\omega^2 x^2}{...
0
votes
0answers
24 views

Notation of physical quantity with applied operator

I'm writing my Bachelor's degree at the moment. I have one equation expressing the force generated by a rotor depending on the angular velocity $\omega_m$. At the moment it is written as $$ F_m(\...
0
votes
1answer
82 views

Does $E=mc^2$ have a constant? If not why? [duplicate]

When I Google the units for $E=mc^2$ it says m is mass in kg speed of light is in m/s and energy is in joules. Why does there not need to be some sort of constant? Why does the total energy in joules ...
0
votes
1answer
68 views

If gram isn't part of the SI system, then how is it that SI recognizes its symbol?

If gram is of the CGS system of measurement (which is a variant of the metric system, which is still used), then how does SI recognize its symbol? When it is not part of SI. What does this statement ...
2
votes
0answers
102 views

What does it mean for $2\pi = 1$ in a “private system of units”?

I saw the following image of an excerpt from Robert Mill's Tutorial on Infinities in QED, floating about the internet: The book is available here, however I don't think I have access to it, unless ...
0
votes
1answer
16 views

How does an accuracy specified in vol% translates to ppm?

I need to setup some CO2 concentration measurement. The datasheet of the sensor is: Range: 0 to 25 vol% Accuracy < 0.5 vol% + 3% of measured value vol% is the percentage by volume. So the range ...
-1
votes
1answer
77 views

Convert metres to the 1.25 to metres [closed]

I have been given a constant, of value $\beta=3$ x $10^{-30} Jm^{1.25}$. I need to use it in an equation that gives a value in SI units (metres). How can I convert the value of the constant $\beta$ to ...
1
vote
2answers
30 views

Problem calculating the ground state radius of Toponium using strong force potential for short ranges

If it were true that the top quark were stable we could, in theory, have a hydrogen-like bound state consisting of toponium $T \bar{T}$. Looking at the strong force, for small ranges it takes the form ...
0
votes
1answer
41 views

Why is the decimal system a more convenient system? [closed]

Can you give reasons as to why decimal system is a more convenient system? I got this in the chapter Units and Dimensions.
1
vote
2answers
119 views

Why don't we take the universal gravitational constant $G$ to be equal to 1 in $F= \frac{Gm_{1}m_{2}}{r^2}$?

In the derivation of Newton's Second Law, we get to an equation $F=kma$. Since this equation is essentially defining force, Newton could have taken the value of $k$ to be anything. For the sake of ...
0
votes
3answers
67 views

When and why are units measured in degree?

I was always under the impression that a unit is measured in degree if it is a relative unit. While this is true for temperatures and angles, I cannot find any reference to this definition or any ...
0
votes
1answer
42 views

Symbol of quintal

Depending on the source, I have come across the symbol of quintal as 'q', 'qt'and 'qtl'. Is there a standard symbol for quintal. If yes what is it?
2
votes
1answer
47 views

Why do the sensitivities of magnetometers and gravimiters have such strange units?

It looks like the sensitivities of magnetometers and gravimeters are usually reported with the units of $\text{Tesla}/\sqrt{\text{Hz}}$ and $\text{Gal}/\sqrt{\text{Hz}}$, respectively (where "Gal&...
0
votes
0answers
26 views

Ambiguities regarding dimensions of Planck length

There is a couple of posts circulating around about how to express higher dimensional (Newtons) gravitational constants in terms of each other. In these discussions, summarized below, there is one ...
1
vote
3answers
66 views

Are absolute and relative temperatures really the same quantity?

Different units for the same quantity usually only differ by a multiplicative constant, such as inch and meter, but °F and K differ by both a multiplicative constant and an additive one. Does that ...
2
votes
0answers
33 views

Going from 4d Planck mass to 3d Planck mass

I have an expression where I have converted all units such that the answer is expressed in 4d Planck mass, $m_p^{(4d)}$. In David Tong's lecture notes, Newtons gravitational constant in 4d is given by ...
2
votes
6answers
3k views

What is the definition of unit vector?

In many physics textbooks it is given the following definition of unit vector: "A unit vector is every vector whose magnitude is 1 unit". I don't like this definition. On one hand, it is ...
4
votes
4answers
5k views

Do units have to make sense in Physics?

For a lack of a better title and phrasing of my question, I am asking: do units have to make sense in physics? Let me give an example of what I mean. Let's say that I have some arbitrary units (for ...
3
votes
2answers
88 views

Why do we set the number of degrees of freedom of an electron in a gas to 2 rather than 3?

I was reading up on basic properties of plasmas and came across this description in the Wikipedia on how to convert between eV and Kelvin units to describe the amount of energy of the electrons: The ...
0
votes
1answer
33 views

How do exponents of a unit of physical quantity affect converting between different prefixes of the same unit?

Lets say I have some 'quantity' in units (kg)^-1/2, I now want to express the quantity in g^-1/2. Do I simply multiply the quantity by k^-1/2 which is approximately 0.0316? The way I am going about ...
0
votes
3answers
79 views

Degrees vs radians [duplicate]

I’ve been messed over on a test (at least one that I can clearly remember, probably at least a few more) (and it was only a few points, but still very frustrating) because I forgot to switch my ...
0
votes
1answer
96 views

What does 'seconds squared per meter' mean?

I was wondering about the meaning of seconds^2 / meters (more specifically, period^2 / length - of a pendulum, after the square root graph of period vs length is linearized). I know that acceleration ...
1
vote
0answers
26 views

What is the value of the universal gas constant in atomic units? [closed]

On Wikipedia the value of the universal gas constant is given for various units but not for atomic units. It should be easy to figure it out but I keep getting it wrong.
0
votes
1answer
35 views

Can I safely replace the speed of light by 0.5 in equations?

In natural unit we set (for example in QCD) c->1, hbar->1, k->1. All quantities can be expressed in terms of MeV. After the calculation, one can simply add c=3*10^8 properly. However, if I ...
17
votes
9answers
3k views

How are physics theorems so accurate, relative to fixed measurement systems? [duplicate]

I admit this sounds like a dumb question. I know very little about physics, but I've always wondered that given the fact that: A unit of measurement is a very specific constant value. Then how can a ...
-1
votes
1answer
37 views

Transform lbm.in/min² into Newton [closed]

The units of physical quantities are important for the transformation of units, achieving coherence. So I need to transfom 10000 lbm.in/min² into ...
0
votes
1answer
36 views

Dimensional analysis physics [closed]

In a certain system, the units of length, mass and time are chosen to be 1 cm, 100 g and 10 s. The unit of kinetic energy according to above sys- tem of unit, will be N erg. Find the value of N. I did ...
0
votes
2answers
81 views

What does a.u. mean as unit (not astronomical unit) in graphs in physics publications?

For example, in this paper (also arXiv), it uses a.u. as the unit in multiple graphs for the quantiy $\frac{dI}{dV}$, for example in Figure 3. I am suspecting a.u. means "appropriate unit," ...
5
votes
0answers
63 views

Are there any units of measurement (other than the ohm) that are represented by non-latin characters? [closed]

We have the prefix μ and the unit Ω, but other than that we seem to not use any other greek letters (or any non-latin symbols for that matter) for specifying units. All other units – meters, seconds, ...
0
votes
1answer
64 views

How to define “unit spatial length” in general relativity?

Suppose I have a metric with time-independent $g_{\mu\nu}$. Suppose I have a small measuring rod at some spatial position and I define it to be of unit length. Will it still have unit length when it ...
0
votes
2answers
85 views

How does a proper motion displacement of $x$ arcseconds/year mean a star is moving at $x$ AU/year?

I trying to understand the author's answer to this question: I don't understand the part underlined red. How does 3.6pc mean 3.6AU? It says a "distance of 3.6AU", but doesn't say what is ...
0
votes
0answers
7 views

Is it possible to extract real physical values from multiphase LBM simulation with Shan-Chen force?

Is it possible to extract real physical values from multiphase Lattice Boltzmann method simulation with Shan-Chen force? SC force is of the form $$\vec{F^{SC}} = -\psi(\vec{x}) G \sum_i w_i \psi(\vec{...
0
votes
0answers
23 views

Derived units described with multiple 'per's

In a dimensional analysis problem, a rate was given textually as so many "Milliliters per Kilograms per Day". This seems ambiguous, as one could either interpret it as A:: Ml / (Kg / Day) = ...
0
votes
1answer
34 views

Meaning of a product of two physical units [duplicate]

I am having a hard time to understand the meaning of measurements that involve a product of physical units, like $10\, \rm N\cdot m$ ($10$ Newton-meters), $3.33\, \rm J\cdot s$ ($3.33$ Joules-second),...
1
vote
0answers
55 views

Why did the scientific community stop using hydrogen as the main measure for the atomic mass unit?

The only thing I could find is that the community switched form one hydrogen atom to 1/16 of Oxygen-16 (which they thought to be the only isotope that exists at time because they had no concept of ...
0
votes
1answer
59 views

Understanding the meaning of the integral of energy of an $\rm H$ atom

This is probably very basic but my notes are confusing and not clearly written so I would appreciate some help in trying to clarify the following points: If we consider the expression $$\left\langle \...
0
votes
1answer
41 views

How to express the force of a GPU in Pound-hours?

I am training a neural network on a small cluster of GPU-equipped computers. Out of curiosity, I would like to express the force of the running GPU's in terms of the force required for a car to remain ...

1
2 3 4 5
20