Units Definition and 975 Threads

Homework Statement alright so i have to find the density of a clay unit. I am given a specific weight of the clay as 120 b/ft^3, the gravity constant as 32.17 ft/s^2. i need to find the density of the clay, i have no problem arranging the equation below to solve for density but I am not used...

Ok so I have done around 1.5 years of maths, science and engineering classes (12 subjects) and realized I didnt enjoy engineering (my major), so I have now changed from a bachelor of electrical engineering to a bachelor of science. Now I am want to include a maths major in the degree however I...

I'm having some trouble with a few problems that I'd really appreciate some help with. 1.) The velocity of a space shuttle is 8 x 10^3 meters/seconds I have to convert this to kilometers/hours. I know there are 1000 meters in a kilometer, and 3600 seconds in an hour. Next I have to...

Homework Statement I always have problems when changing units form Joule form to Megaelectron Volts and vice versa...whats the easiest way to find them? Homework Equations The Attempt at a Solution I always get confused at the conversion part.

Homework Statement A man was standing on a cliff when he dropped a stone. One second later, he dropped another stone. How long before the distance between the two stone is 10 meters? (Show solutions with special attention to deriving the units.) Use g=10 m/s^2.Homework Equations Let d_1 =...

Homework Statement bernouliis equaton P + 1/2 Rho v^2 + Rho g h = constant find the units of the three terms on the left hand side & show they are the same and then the units of the constant on the right The Attempt at a Solution all i can think to do here is check the SI units...

Hi all, I would like to know if any of you know about anything the equivalence of SI units for differential equations? For example, for the equation E=mc2 SI units for RHS must equal LHS. I am wondering if this would apply to differential equations? I recently came across a journal paper with...

What are the dimensions of a scalar field \phi ? The Lagrangian density is: \mathcal L= \partial_\mu \phi \partial^\mu \phi - m^2 \phi \phi So in order to make all the terms have the same units, you can try either: \mathcal L=\frac{\hbar^2}{c^2} \partial_\mu \phi \partial^\mu \phi -...

This is hubbles constant from my source 74.2 ± 3.6 (km/s)/Mpc What does the ± mean?

Hi, I've come across a number density expressed in units of Mpc^-3 dex^-1; I understand the Mpc^-3 but not the dex^-1. I know dex is some kind of log scale with n dex = 10^n but I'm not sure what dex^-1 means and was wondering if anyone could help. Thanks!

Homework Statement A chemical plant produces pesticide that contains a molecule potentially harmful to people if the concentration is too high. The plant flushes out the tanks containing the pesticide once a week, and the discharge flows into the river. The molecule breaks down gradually in...

the unit of cosmic ray flux is expressed as flux /(m^2.sr.s.GeV), so what does sr stand for? Thanks.

Hi there, So I have a multi year time series of of heights in meters that I am working on. If I compute the FFT on the data and then calculate the amplitude as: abs(FFT)/N where N is the number of samples what units do I end up with for the amplitude? Is it still in meters? Cheers

Hi, I have been viewing some publications related to space weather and have noticed that in many graphs and in the articles, the units AMeV appear very often. I am wondering what the A is for? My best guess is that means atomic, ie relating energies of ions rather than single electrons...

Multiple Choice Question: What are the units of the spring constant K? I. N/m^2 II. kg/s^2 III. J/m^2 Choices: A. I only B. II only C. III only D. I and II E. II and III I cannot find it in my textbook for some reason...

Where is it proven that the unit of area in Euclidean geometry must be a square with side=1? Or is it an axiom? Why not triangles or circles to represent area?

hello everyone. a little question...(or mybe two...)... why does vickers and brinell hardness test have the units of stress ? and why does rockwell test has no units at all ? thanks to all !

I was just studying the Bhor theory and found that if we assume energy is quantised in (nh/2pi) then we can say that the angular momentum of electron is mvr=(nh/2pi) , but the units of (nh/2pi) is joules(Kg m2/s2) as it is energy and of mvr is Kg m2/s so how is it possible to equate them?

I am stuck with Gaussian units. If the field in vacuum is E = \frac{Q}{r^2} Is the field in a dielectric E = \frac{Q}{\epsilon_r r^2} , or is it unchanged?

How can I work out how many units of electricty are consumed in problems such as the following? During one day, a 2.5 kW appliance was used for 8 hours. How many Units of electricity were used? I know that the answer is 20 but I have no idea how that figure is arrived at. Also, in what...

Sorry for asking this dumb question. The units for displacement is m. The units for velocity is m/s. The units for acceleration is m/s^2. When dealing with kinematic problems would it be incorrect to have units such as km, miles, and minutes in the answer? Should they be converted to...

Homework Statement A centripetal-acceleration addict rides in uniform circular motion with period T = 2.3 s and radius r = 2.80 m. At t1 his acceleration is = (6.60 m/s2) + (-2.40 m/s2). At that instant, what are the values of (a)v dot a and (b) r X a ? Homework Equations i know the...

Need to know how to figure out the units on a slope ty.

Homework Statement In an equation of the format y=mx + b, where y=(m1-m2)g and x=acceleration (m/s2) ... what are the units for m and b? (I know that m is the slope and b is the y-intercept, but what do they mean?) Thanks :)

I am studying in Grade XI and have started with physics. Its very different from physics in last grade. So here are my questions about few units my tution teacher challenged everyone about. Homework Statement i)What is the name of the unit [Kg][Meter][Second]^{-3} - We may write it as...

I am studying in Grade XI and have started with physics. Its very different from physics in last grade. So here are my questions about few units my tution teacher challenged everyone about. Homework Statement i)What is the name of the unit [Kg][Meter][Second]^{-3} ii) What is...

Homework Statement I am asked to convert moment of inertia of a spacecraft from slug-ft^2 to N-m^2. Homework Equations The Attempt at a Solution Is this a trick question? Usually moment of inertia is expressed in kg-m^2 not N-m^2. 1 slug = 1 lbf-s^2/ft --> therefore 1...

Are Planck units the same in all frames of reference ? If so, shouldn't the theory of relativity be modified to account for this ? (same as considering the speed of light the same in all reference frames) Because in it's current form, for a large enough velocity, through length contraction we...

1.What are the basic units for a) wavelenght of light b) frequency of light c) speed of light 2. What is the wavelenght, in meter, of radiation that has a frequency of 5.11x10^11 s^-1

I made a mistake I meant km/h to m/s^2. 1. ThrustSSC, the world's first supersonic car, accelerates from rest to 1000km/h in 16 s. What is its acceleration in m/s? 2.a=v/t = v-v0/t-0 3. I'm not sure how to change units (Professor didn't show me.), so can you please now all the work to the...

I was always puzzled by the fact that while almost all Planck units are extreme (very high or very low), Mass and Energy are exception from that rule. Planck mass is in the ‘middle’ of the spectrum, and it divides the mass spectrum into 2 parts: For small masses/energies m << Mplanck we can...

Homework Statement A mouse has an pupil diameter of 2.5 mm. lying 200 meters from the mouse are two stones 30 cm apart. λ = 500 nm a) what angle do the stones subtend? b) what is the MAR (minimum angle of resolution) of the mouse's eye. Homework Equations question a) tanθ = O/A O= 0.3 m A= 200...

Hi all, I'm working on a problem where I have to find the time it takes for a planet to form from a protoplanetary disk, using the equation: t = \frac {3}{A}M^{1/3} Where A= ( \frac {(1+2\beta)\sigma}{P}) (\frac {3\pi^2}{4\rho_m})^{2/3} However, I'm not sure which units the...

Homework Statement I am trying to get the units to match up on both sides. \frac{\partial T}{\partial t} = \frac{\nabla ^{2} T}{k} = \frac{1}{K}(\frac{\partial ^2 T}{\partial x^2} + \frac{\partial ^2 T}{\partial y^2} + \frac{\partial ^2 T}{\partial z^2}}), where k is the thermal resistivity...

Whenever I see the amplitude for fermion scattering, it comes out dimensionless. However, for scalar scattering, the dimensions are 1/energy^2. For example, for 2 particles scattering into 2 particles in a \phi^3 interaction, there is just one internal line, so the amplitude is proportional to...

Homework Statement A series RLC circuit has a resonance fre- quency of 1360/ Hz. When it is operating at a frequency of ! > !0, XL = 9.7 and XC = 9.3 . Find the value of L. Answer in units of mH. Homework Equations X(L)=w*L The Attempt at a Solution what i did is...

It seems to me that solar power and air conditioning are made for each other. As of now there are several different companies making smaller adsorption/absorption AC units, but they are overpriced compared to their electric driven counterparts giving limited return on investment. Here's what...

Tensors and Units Consistency Where do the unit labels go on tensors? This discussion is continued from this thread https://www.physicsforums.com/showthread.php?t=321298" Greg, I've been trying to make sense of things in mixed units. Taking the dot product as you've done is a good test...

What are the fundamental base units for Force and Volume? I think its cm3 for volume but not completely sure.

I've been reading a bit on vector calculus trying to get a solid grasp on it. I am wondering how it can be stated that given C=AXB (all vectors), that C is equivalent to the area of the rectangle formed by A and B in the A,B plane. How can you equate length and area. One is in say...mm and the...

Homework Statement In the ring Z[\sqrt{-3}] find all units and prove that 2 is irreducible but 7 is not. Homework Equations The Attempt at a Solution Well a unit is a non-zero element of the ring that when multiplied by some other non-zero element of the ring gives the unity of...

This is my first assignment in my Modern (Abstract) Algebra class, just to give an idea where I am with tools that I can use. Homework Statement Describe all units and zero divisors in Z[i] Homework Equations The Attempt at a Solution I already know the answers are units = 1...

I'm searching for an online text on units, units systems, dimensions, dimensional analysis and so forth. A nice overview or summary, or an introduction not geared to the complete beginner. Has anybody a good link? thank you

Homework Statement "A gas storage system contains oxygen at a pressure of 5 atmospheres at 300 K. (Here, you may assume that oxygen behaves as an ideal gas.) The volume of the cylinder is initially 150 L. (State 1.) In a fire the gas is initially heated by 200 K, with a safety system keeping...

Homework Statement Hi, I need to know the correct SI units for Einstein Coefficients (A and B) for stimulated emission (say laser). The equation I'm on about is Homework Equations \frac{A}{B} = \frac{8\pi h\nu^{3}}{c^{3}}The Attempt at a Solution after some scribbling I got to \frac{A}{B}...

Homework Statement A quantity, d, depends on the angular frequency in the following manner: d=ω C √(l/g) sin(ω K √(l/g)) Determine the units of C and K Homework Equations d=m ω= sec-1 l=m g=m/s2 I substituted this into the equation m=s^(-1) C √(m/(m/s^2 )) sin(s^(-1) K √(m/(m/s^2 )) )...

While reading a paper on optics, I came across "the radiance of the projector is 20 mW/cm2, expanding out onto an f/18 cone." What does the "expand out onto an f/18 cone" part mean? I thought that radiance is just in units of power/area/steradians. What does f-number have to do with anything?

Homework Statement The fundamental vibrational frequency of gaseous 14N16O is 1904 cm-1. a. Calculate the force constant, using the simple harmonic oscillator model Homework Equations K=u((2pi)(v))^2 u=reduced mass The Attempt at a Solution u=[(14)(16)/(30)] (1kg/6.02e^26)=...

Not quite sure if this is the correct place to post this, but I am having difficulty converting between AE and SI units. Having grown up using only SI units, the AE units are a little confusing. What is the conversion formula for degrees Fahrenheit to degrees Celsius incorporating a degree...

Homework Statement I need to convert a value in cm^3s^-1 to litres per second. I know that 1 litre=10^-3m^3 Homework Equations The Attempt at a Solution Could someone please help?