Units Definition and 975 Threads

Hi everyone I have the following problem: Homework Statement Give is the following potential for a molecule: E_s(R)=E_s(\infty)-\frac {1}{R}+A*exp(-cR) whereas E_s(infinity)=1.49 eV. A and c are constants which I want to calculate. R(equilibrium) is given as 2.36 Angström and the...

Hi Everyone, I hope this is the best place to put this topic if not I do apologize! I'm currently pursuing an IT degree in software development and plan on studying a few related mathematical units that I believe would be beneficial to me. In this regards, Discrete maths, Calculus and Linear...

In case I'm wrong, the formula for energy of a photon is E=hf. Or E=hc/λ, because f=c/λ. Basically the second formula is just in case you don't know frequency so it crams the equation for that into the equation for energy. When I use E=hc/λ the units I get are... kg*m2/s3 What I did was... A...

Reading in Russian sources I see they use ballistic coefficients such as these: BC = 3.0 kg/m^2 or alternatively BC = 3.0 m^2/kg That's quite different than the usual G1, G7, etc. Given a certain muzzle velocity, how do I use that to calculate velocity at some point downrange?

So in a spacecraft with regular air at 1 atm pressure, a hole gets punched in it (depressurizing it). I'm looking for the Exit Velocity of the air at t=0. Using Units: Internal Pressure: Pi = 1 atm = 101300 [kg / m*s2] Air Density: \rho = 1.2 [kg / m3] And Equation: Pi = 0.5 * \rho * (Ve2)...

While I do understand the use for the displacement vector D = (e0)E + P, I don't quite understand why they label it as "flux density". The units for the displacement vector are C/m^2. The units for electric flux are Vm, so wouldn't electric flux density become Vm/m^2 = V/m which is just equal to...

If two units have the same dimensions are they always inequivalent? I was thinking, would doing dimensional analysis on units prove they are equivalent or could they have the same units but not be equivalent.

Does anyone know of a dimensional formula for the Coulomb in SI that does not involve amperes as in A*s? I am looking at some equations and the dimensional analysis is leaving me with C (Coulomb unit charge) and left over m, kg, s to various powers. Just curious if anyone has come across some...

Homework Statement Calculate various fuel quantities for Flight 143. The plane already had 7682 L of fuel ob board prior to flight and tanks were to be filled so that a total of 22300 kg were present at takeoff (a) Using the incorrect conversion factor of 1.77 kg/L calculate in kg the...

I don't get this. Everywhere I look, the units of transmittance of light are dimensionless. I get that it's a ratio of incident to transmitted radiation, t(f) = I(f)/T(f), and these two have the same units. However, light intensity is always properly defined as the power per metre squared...

Hey guys, I'm currently working on a chemistry setup and we're building some protocols. We decided that every communication on the protocol between two devices will be in SI units. However, for a data descriptor I plan to use 4 bits per standard SI unit. This means that units for variables can...

Homework Statement The 8 lb uniform rod AB shown in the figure rotates in the vertical plane about a pin at C. The spring attached to the rod at D has a spring constant of 1.25 lb/in., and its unstretched length is 24in. If the rod is released from rest in the position shown, determine its...

All, please help me refine, restate, explain, understand, expand, add, remove, answer the below statements/ questions. Thanks in advance. 1.) Voltage is considered a scalar quantity. (J/C in SI Derived Units) which is a magnitude of energy per coulomb...no direction with this example. Some...

In my lectures the equation for current density was given as: J=n*q*vd where: n = the number of electrons per unit area q = electron charge vd = drift velocity of electrons If you rewrite this equation as: J=\frac{N}{A}*q*\frac{dr}{dt} where: \frac{N}{A} is the number of electrons per unit...

I read that a C12 atom has an atomic mass unit of 12 amu's. A C12 atom has 6 protons, 6 neutrons, and 6 electrons. If the mass of a proton is 1.00728 amu, the mass of a neutron is 1.00867 amu, and the mass of an electron is .000549, how can it's total amu be 12...

Homework Statement The potential difference between two points is 140mV. If 280μJ of work are required to move a charge Q from one point to the other, what is Q? Homework Equations Q = W/VThe Attempt at a Solution http://imgur.com/FDaQfb9

Homework Statement A sample of aluminum oxide, Al2O3(s), contains 8.29*10^25 total atoms. Calculate the amount in moles of aluminum oxide in the sample. Hint: This is a two-step problem. Calculate the number of formula units first.Homework Equations N=N × N_{A} The Attempt at a Solution...

I am reading a paper where the bending power of a dipole magnet is described as 2 Tm. Is that Tesla*meter? Is bending power actually power i.e. Work/Time? Can someone explain this physical quantity to me, please?

The decision has been made to install a wind farm with 2000MWe of generating capacity. The rest of the question gives the average wind speed (m/s) air density (kg/m^2) turbine efficiency (%) blade length (m) all of which are used to calculate the power production of the turbine, in...

|ψ(x,t)|2 is the probability density. Probabilities are dimensionless. What would the SI units of |ψ(x,t)| be, then? Also dimensionless?

Homework Statement Find the units of k1, k2, k3, k4, and k5. Write rate reactions for dA/dt a. A\leftrightarrowB k1 (forward) k2 (backward) b. A + B \rightarrow C k3 (forward) c. A + R \rightarrow 2R k4 (forward) d. A \rightarrow B k5 (forward) Homework Equations...

I just have a question concerning a previous thread about gravitation. The formula is from post 19 at https://www.physicsforums.com/showthread.php?t=635188&page=2 v= dr/dt a = dv/dt multiply by dv/dt by dr/dr: a = (dr dv)/(dt dr) = v dv/dr This gets you to the first step...

What qualifies for being called a fundamental quantity and having its own fundamental unit? For example length is considered fundamental quantity and it has a unit of meter. But Area isn't considered fundamental. Is it because we know area can be CALCULATED by multiplying the length of the two...

Homework Statement Let R be a ring with identity, and a,b are elements in R. If ab is a unit, and neither a nor b is a zero divisor, prove a and b are units. Homework Equations If ab is a unit then (ab)c=1=c(ab) for some c in R. The Attempt at a Solution Assume both a and b are...

Homework Statement Determine the force necessary to accelerate a mass of 20 lbm at a rate of 60 ft/s^2 vertically upward.Homework Equations How do you properly account for weight? What exactly is pound force? How do you go from pound mass (lbm) to pound force (lbf)? The Attempt at a Solution F...

I'm slightly confused about natural units. Take mass as an example: I can measure something in kg's, but then decide to convert to MeV/c^2, for instance. To do that I would multiply the quantity in kg by 3*10^8 squared and divide by 10^6*1.6*1-^(-19) i.e. the SI values of the constants. If I...

Hello, Planck units are defined here http://en.wikipedia.org/wiki/Planck_units Length, mass and time are defined via G, c and \hbar and do not involve kB; But temperature contains all G, c and \hbar and kB; Perhaps this is okay; just seems "uneven" that kB appears with a zero power in...

Homework Statement The reading on a mercury manometer at 25 degrees Celsius (open to the atmosphere at one end) is 25.62 inches. The local acceleration of gravity is 32.243(ft)(s^2) Atmospheric pressure is 29.86 (in Hg). What is the absolute pressure in psia being measured? The density of...

Google Translator.: (Portuguese(Brazil) -> English(U.S.A)) Hello, good morning. I live in Brazil (South America). I'm doing research for the course in production engineering. I found that in Brazil, we use the international system of units...

The formula for magnetic pressure is P_{B} = \frac{B^{2}}{2\mu_{0}} Now, the units on the left hand side are clearly Pascals, but the units on the RHS are T^2 H^-1 m. I've been trying and I can't see how to make the units on the RHS equal the units on the LHS. does anyone have any insight?

Homework Statement find the radius R3=((T2GM/(4∏2))1/3 The Attempt at a Solution simple enough, my only question is when I plug in T (units: sec) G (units: m/s^2) and M (units: kg) there is nothing to cancel out the kg so my R is not in units of meters...the equation is correct because...

The equation of interest is: A=B*V^n where A has units of W/(m^2*K) W=watt, K=kelvin, m=meter V has units of m/s. B and n are parameters to be determined.I have a set of values that I put into excel to generate a plot. From the plot, I fit a power trendline to it and got the equation to be...

Hello, Could someone help me finish this train of thought? This is how we think in SI units: First, just because we like the value of 1 Ampere as it is now, we choose the force between two parallel conductors to be exactly 2×10^{-7}N= const ×\frac{1A×1A}{1m} Then, purely as choice, we decide...

Hello, I was reading about a comparison betw. Gaussian and SI units and the author states "The main advantage of Gaussian units is that they make fundamental physical issues and theoretical relations involving electromagnetic phenomena more clear." Would someone know - is the advantage...

Pascal-seconds is a unit of viscosity. Why? I know that viscosity represents the thickness of a fluid, or its ease of flow, but I don't understand why that is represented by these parameters.

How is (density)(gravity)(height) supposed to equal pressure? density = kg/m^3 gravity = m/s^2 height = m (kg/m^3)(m/s^2)(m) = (kg/m*s^2)

Homework Statement A proton has a diameter of about 1fm. Estimate the minimum momentum in units of MeV/C of a quark confined in a proton. Homework Equations The Attempt at a Solution I used the uncertainty relation \DeltaP\DeltaX ~ \frac{\hbar}{2} \DeltaP ~ \frac{\hbar}{2 x...

Hello, I need some help with this question, it is not very clear and I find it hard to translate from text to math... Some company has found that x units of it's product can be sold for p$ a unit when x=1000-p. The cost of producing x units in a day is C(X)=3000+20x. A. Found the income...

Homework Statement I have a misunderstanding of when I can safely use eV units in a formula. For example in the formula p = \sqrt{\frac{E^{2} - m^{2}c^{4}}{c^{2}}} I can put the energy and mass in terms of MeV and get an answer with units MeV/C, which makes sense. But then there was this...

I am working on a project about pollution emission, but I am not a chemist. I am seeing the units ppmC, ppmC3 and ppmC6 almost everyday, and I have trouble understanding what they stand for. The only definition I get is "Parts per million hydrocarbon concentration expressed as methane (for...

Please can anyone help me?I'm confused here. If I'm following unit of force as Newton, and length as mm; and stress as MPa,then for a consistent system of units (see link below); http://www.dynasupport.com/howtos/general/consistent-units/ what should be the unit for: 1)density 2) rotation

Mole is just a number. It doesn't really measure anything so why is it a fundamental unit? And with kelvin - it represents the average energy of the atoms/molecules in a compound. Why is it a fundamental unit? Temperature can easily be represented in joules.

Folks, I am trying to understand the balance of units for this eqn ## \displaystyle \frac{d^2}{dx^2}(E(x)I(x) \frac{d^2 w(x)}{dx^2})+c_f(x)w(x)=q(x)## where ##E## is the modulus of Elasticity, ##I## is the second moment of area, ##c_f## is the elastic foundation modulus, ##w## is...

Hi, Suppose we have f(x) = x3. Integrating this function using the definite integral with the upper boundary being 3 and the lower boundary being 1 would result in 20. Does 20 have any units or is it unitless? Seeing how it is the area underneath a curve, I would imagine that it has square...

Is there a reason why e doesn't have units attached? I've kind of just accepted it but was wondering the reason behind it.

Hello everybody! Once again, someone searched elsewhere in September a project topic for her software class, and I suggested one in November , so this topic as well must be available to other people... A piece of software could check that the units of an equation fit together, like: a...

Homework Statement In what units is energy density measured? 1. Watts 2. Watts per cubic meter 3. Newtons per meter 4. Joules per cubic meter Homework Equations E = cB (as derived by Maxwell) The Attempt at a Solution This question is so basic yet I'm confused. I thought...

Hello. I have a problem with the statement that specific values, like the speed of light, have no meaning because we can change these values by a change of units. For measures attached with units the value(number) has no meaning "per se", I'm ok with that. (Unlike pure numbers like ratios...

Homework Statement Venturi effect nozzle.. Starts off at 100cm and goes down to 40cm. The flow rate of the gas is 2.23 m3/s. What is the average velocity at the beginning and end of the nozzle. Homework Equations Continuity Formula, Bernelli = Q = A1V1=A2V2 The Attempt at a...

Homework Statement In a physics lab we were finding slope on semi-log graph paper, with the y (up) axis representing tension in Newtons, and the x (sideways) axis representing θ in radians. Sadly, the prof introduced the new concept of natural logs to me - I'd never heard of these until this...