Units Definition and 975 Threads

Homework Statement Exercise Find the pressure at a depth of 10 m below the surface of a lake if the pressure at the surface is 1 atm. (Answer: With P0 = 1atm = 101kPa, ρ=103kg/m^{3}, and g= 9.81 N/kg, we have P = P0 + ρgh = 1.97 atm. The pressure at a depth of 10 m is nearly twice that at...

I've been looking at the various Planck units, and I'm wondering how they are constructed from the constants involved. Like is there any physical reasoning behind those equations? I've looked all over the place for derivations of the equations or what the actual physical meaning of the units...

Time and time again I always hear people say that Planck Lengths are the smallest units of meaningful distance. But I don't think this implies nothing can be smaller than this or that spacetime is discrete, correct? It just means talking about anything smaller than this would be like talking...

Hello, Just wondered what the correct way is to display physical units on chart axes. Let's say for example thermal resistance of a heatsink extrusion is plotted as a function of length, and so the units for the y-axis are K.W-1 My 'A' Level physics teacher always insisted on (in order...

There are different types of CCB units. Hydraulically powered, pneumatic, electromagnetic and of course mechanical. But, can anyone give me the proper advantages and disadvantages of electromagnetic CCB over other variants. Googled it. But invain. Regards.

I've been reading about calculating dissolved gas concentrations in water at varying temperature and salinities using an equation of the form: ln(β)=exp(A1 + A2*(T/100) + A3*ln(T/100) + A4*(T/100) + S*(B1 + B2*(T/100) + B3*(T/100)^2 where β is in units of mL/L, and A# and B# are...

What is the meaning of a frame of reference where $c=1$ ? Are these the so called natural units?? And which is the purpose of this??

1. An electric train initially moving at 25km/h accelerates to 35km/h in 20s. Find its average acceleration in m/s^2. G: v1 = 25km/h v2 = 35km/h Delta t = 20s R: Aav 2. Aav=(v2-v1)/delta t 3. = (35km/h-25km/h)-20s The problem is that the velocities are in km per...

Homework Statement Hi I'm having trouble solving this physics problem if anyone can help it would be greatly appreciated ! Static pressure problem: A bathtub contains water to a depth of 20 inches. Determine the pressure at the bottom of the bathtub in both [psia] and [psig] (a being...

Homework Statement Hi I'm having trouble solving this physics problem if anyone can help it would be greatly appreciated ! Static pressure problem: A bathtub contains water to a depth of 20 inches. Determine the pressure at the bottom of the bathtub in both [psia] and [psig] (a being...

Homework Statement A x cm long wire has a diameter of y mm and a resistivity of 4.0x10-7 ohm-cm. Calculate its resistance. Homework Equations R = p*L/A The Attempt at a Solution First, I convert the given information into SI units: Length = x*10^-2 m Diameter = y*10^-3 m...

In class, we're learning about recursive functions. One example given was figuring out 1 + 2 + 3+ 4 + 5 + 6 + 7 + 8 + 9 + 10. My professor stated to address this, we start with 10 in the function and decrement for the next recursive call, so 10 + f(9). He said going the other way would be...

After the discovery of the speed of light, it may have made a bit of sense to redefine the meter as \frac{1}{300,000,000} the distance light travels in a second. I understand that larger units like the light year may have been distorted a bit, and that conversions would be required for such...

Homework Statement An Earth satellite is observed to have a height of perigee of 100 n mi and a height of apogee of 600 n mi. Find the period of the orbit. Homework Equations (1) Period = (2*pi/sqrt(mu)) * A^(2/3) (2) rp+ra = 2A Where: Mu is the Standard Gravitational Parameter...

Homework Statement Consider a submarine cruising 32 ft below the free surface of seawater whose density is 64 lbm / (ft^3). What is the increase in the pressure in psi exerted on the submarine when it dives to a depth of 172 ft below the free surface? Assume that the acceleration due to...

Homework Statement #5 and #6 of the attached pdf on page 5 (graph on page 4 relates to said problems) Note: The professor did not cover how to do a problem like this, and the book does not have a similar problem, nor any other handouts. This definitely was a unique question. I'm unsure if I...

This is maddening and i cannot find a concise explanation anywhere despite the simplicity of this question. I keep coming across faradays law expressed as \text{curl}\left(\mathbf{E}\right) = -\frac{1}{C^2} \frac{\partial\mathbf{B}}{\partial t} Im only used to working in SI units so all i...

Homework Statement Given that gcd(n,m)=1, prove that \mathbb Z_{nm}^\times = \mathbb Z_n^\times \oplus \mathbb Z_m^\times. Homework Equations / The Attempt at a Solution I can prove both groups have the same amount of elements (using Euler's totient function), but I can't figure out...

Generally, I see Avogadro's constant being given with units mol-1. Now to me that doesn't seem very... descriptive. But as they say there's more than one way to skin the cat, so I was wondering if these other ways of thinking of it are correct: The conversion factor from grams to amu. The...

Homework Statement I need to infer the observed star formation efficiency of the Kennicutt Schimdt law starting from a volumetric SF law. The KS law is a relationship between gas and stellar surface density that we can approximate as: \frac{d\Sigma_*}{dt}=A\Sigma_{gas}^{1.5} Where A...

if using hbar=c=1 and ev for mass/energy what are appropriate distance units? Wikipedia talks about inverse energy without really explaining them

Homework Statement During a short interval of time, the velocity v in m/s of an automobile is given by v=at^2 + bt^3 where the time is t in seconds. The units of a and b are... Homework Equations The Attempt at a Solution Alright, here's the thing. A friend gave me some old...

Homework Statement "Power is the rate at which work is performed. Power is signified by W for watts. Power is also the amount of energy transmitted in a unit of time (s). Energy is measured in joules. Joules have the units of Newton∙meters. A Newton is a unit of force. It...

Here is a link to page in a book which contains an example problem: http://imgur.com/OPrlw.jpg" In the book, they work out the natural frequency of a hydraulic cylinder and come out with an answer in rad/sec. This number is then inverted to get a time constant, and the resultant unit is...

Homework Statement Two charges, q1 = 4.9 e C and q2 = -3.6 e C are located 105nm apart, what is the size of the force between the two charges?Homework Equations F=kqq/r^2 The Attempt at a Solution I did it according to the formula and I got the answer wrong, so I checked it using an online...

1. Find the number of pairs (m, n) such that 2m - 2n = 63 in which m and n are nonnegative integers. 2. What is the units digit of 625 - 324 ? 3. How many perfect squares divide the number 4!*5!*6! ? 4. What is the last digit of the sum 1! + 2! + 3! + ... + 2010! + 2011! ? Thanks!

Homework Statement I just now came to the realization that I don't know the standard for representing units. When do I include "." after the abbreviation and when do I not? Thanks. For example mi. or mi m or m. yr. or yr What's the rule? I'm sure there's got to be some general...

It only seems to have been mentioned a couple of times in passing, but Alan Eliasen's Frink calculator and programming language (https://frinklang.org/) makes unit conversions simple (converting to SI internally then back to any desired target units. User-defined units may be added, too.) Very...

i have a basic question about the natural frequency of a system. for a mass (M), spring (k constant) undamped system the natural frequerncy is: w_n=sqrt(k/M) the units of w_n according to a lot of resources i found on the internet & textbooks are [rad/sec], my question is why? if i use...

Homework Statement If a 2000 lb car with a velocity of 88 ft/s has by my calculations a kinetic energy of 240 kJ. But for a 909kg car with a velocity of 26.73 m/s I calculate 324.7 kJ. Same velocity, same mass, different energy calculation. Homework Equations English units: Kinetic...

how to convert length units to inverse cm.For example arngstroms,nanometers to cm^-1.Thanks

I have a somewhat mundane question that I hope somebody can help me with. I am working with several standards for performing leak testing on hermetically sealed electronics packages using helium bombing. The question I have is about the engineering units used in the leak test specifications...

Fukushima - Unit 2, what happened different to Units 1 and 3? There are recent discussions about this topic going on, so I think it deserves its own thread. According to attachement IV-2, Unit 2 is responsible for more than 90% of the overall emissions. So there's one big question: What was...

Hi there... I have a differential equation with to terms: \frac{d[Ca2+]}{dt}=f\Big(\frac{3I_{Ca}}{z 4 \pi r^3 F}-k_{Ca}[Ca2+]\Big) I think that the first term converts the Ca2+ (density of?) current to mol units. But, where does it comes from? z is the valence; in this case of the...

Hi, I was curious as to what webers and teslas measure. As I read up on them I was able to speculate that teslas measured a magnetic fields dimensions and webers measured a magnetic fields strength; obviously though, this is a mere speculation: so please correct me if I am mistaken. Thank you

Hello. I have just read a mean free path (a distance) written in units g/cm^2. How do you interpret this unit in terms of the usual idea of the mean free path as a distance?

Hi everybody! Would someone please advise on the following matter. I'm making up a table of railcar operating loads. One of the column includes abbreviated units of measurement such as kN, MN, N/mm2, etc. The question is: How should I title the column? I was thinking about titling it...

I was browsing another topic, and I suddenly remembered that I've never quite figured out what units matlab's fft returns. I've used the fft before and found where I had signal noise by taking the power density of the Fourier coefficients, which is all I really wanted to use the fft for in the...

First post; I am starting to read the official problem description of the http://www.claymath.org/millennium/Navier-Stokes_Equations/navierstokes.pdf" and am having trouble understanding the units involved in the first equation :rolleyes: The equation, verbatim, is \begin{equation}...

The thermal conductivity of wood is 1 BTU per hour, per square foot, for a temperature gradient of 1 F° per inch. Convert this to units of W/mK, knowing 1 F° = 5/9 C° 1 inch = 0.0254 m 1 foot = 0.3048 m 1 lb = 0.453593 kg 1 kcal = 4184 JI know there are conversions between BTU and...

How do you find an infinite number of units of \mathbb{Q}(\sqrt{21}) using the \sqrt(21)? I saw one example using continued fractions but do not know how to apply it in this case. I do have the periodic form of the continued fraction of \sqrt(21).

Hi, I am simulating vibrations in simulink and processing my results in matlab. I am trying plot the PSD for my acceleration results using pwlech method. When I plot the PSD plots from the methods below (NOTE:I have a sampling rate of 0.006 so that means I am using a sample frequency of...

Homework Statement Describe all the units (if any) in each given ring: 2Z X Z with addition and multiplication by components; and Z X Q X Z with addition and multiplication by components Homework Equations The Attempt at a Solution I do not know how to begin, I am not sure how...

We've always been using mm^4, but I see in my answer book (answer written below) that one solution says R^4. Is it the same thing, just that R^4 is used for a circle? The measurement in my exercise are in mm. I did get the answer, I just wasn't aware I was supposed to write it in terms of R^4.

Can someone please explain how kg x kg-2 (in superscript) can equal kg? I hope it does or my calc is wrong! Anywhere I can revise this kind of thing? Mick

Hi, I am trying to find a counterexample to disprove this statement, but can't find any: If S is a subring of a commutative ring R, then U(S) = U(R) \cap S Note that U(X) denotes the set of all the units of a ring X, where x is a unit if x has an inverse in X, such that x times its inverse...

I'm going in circles on units (or perhaps more accurately different unit systems). The two my professor has chosen to work in are Gaussian units and MKSA units. My problem is one of lack of understanding; are the units of measure for electric and magnetic fields in these systems: Gaussian: E...

Hi i have done all the work for this problem calculating viscosity and i come to the last part where i need to manipulate and cancel out units to come to a final solution. The equation works out as viscosity = 0.0042m^2 x 9.8m/s/s x 11,401.4kg/m^3 all divided by 1.034466m/s viscosity is...

Homework Statement Let's consider the a piece of a meteor falling to earth. The gravitational acceleration is experiences if GM/r^2. If I integrate acceleration as a function of r, i should get velocity as a function of r, right? \int \frac{GM}{r^2}dr=GM\int...

M(t) = M0 + n (t - t0) where M(t) = the Mean Anomaly at time t; M0 = the Mean Anomaly at the Epoch time; n = (G*(Me+Msat)/a^2)^.5 = the satellite orbit's Mean Motion; t = the chosen prediction time; and t0 = the Epoch time. My question is...