Units Definition and 975 Threads

Homework Statement Is mA/mV the same as A/V? Suppose I have 6.42mA/26mV the milli's cancel out and give A/V? This is in regards to transconductance parameters for transistors, but it's just a question of units.

Homework Statement A jetliner touches down at 270 km/h. The plane then decelerates (i.e., undergoes acceleration directed opposite its velocity) at 4.5 m/s2. What’s the minimum runway length on which this aircraft can land? Homework Equations v2fx = v2ix + 2axΔx The Attempt at a Solution i...

Homework Statement (T-T envir)/(T int - T envir) = exp (-(2h/pcL)t) T = temp (°C) h = heat transfer p = density (kg/m^3) c = specific heat (J/Kg * K) L = plate thickness (m) t = Time (s) What are the appropriate units for h? Show all steps... (equation is homogenous in units) The Attempt at...

So, I'm trying to brush up on my undergrad physics, and I'm sure this is a bone-headed question, so please bear with me. Homework Statement A heavy object, when placed on a rubber pad that is to be used as a shock absorber, compresses the pad by 1cm. If the object is given a vertical tap, it...

So, I'm trying to brush up on my undergrad physics, and I'm sure this is a bone-headed question, so please bear with me. Homework Statement A heavy object, when placed on a rubber pad that is to be used as a shock absorber, compresses the pad by 1cm. If the object is given a vertical tap, it...

Hey there, I'm in a math class and we're covering some applications to physics and although I completely understand the math behind it and am getting the correct answers, I'm a little iffy on how some of the units work. Would anyone be kind enough to tell me whether or not my thought process...

Hi All and sorry if this is too easy a question but here goes... Sines, Cosines and the rest of the trig functions are the ratio of two lengths and thus are dimensionless quantities. That is if I plug in a value for t in sin(ωt) there are no units. For example the solution of x'' +...

In a lab we conducted in class we graphed angular acceleration vs torque, and found a positive linear correlation-easy enough. However I am getting rather stuck in simplifying the units of slope in terms of Kg, m, and s... I am fairly sure this will give me that angular acceleration equals...

Homework Statement Represent the following combination of units in the correct SI form using the appropriate prefix km*mN Homework Equations k = 10^3 m = 10^-3 The Attempt at a Solution km * mN = (10^3)m * (10^-3)N = m*N = Nm Have I done this correctly?

Hi all, I'm having trouble with the power required formula for steady level flight. Here's the formula: Preq = 4/3*W*sqrt(W/S*2/ρ*sqrt(3*CD0/(π*ε*A))) I'm using this for a small indoor RC fixed wing. The values I'm using are as follows: Weight, W = 0.3924N Wing Area, S = 0.073 m^2 Density, ρ...

I will just paste the link, cause its faster this way: http://scienceworld.wolfram.com/physics/PlanckLaw.html The last equation for spectral energy density if you look at the units you get eVs/m^3 or Js/m^3, yet energy density is supposed to be J/m^3. What am I missing here?

I donated blood at the Red Cross yesterday, and now I'm wondering about some of the claims they make, and whether it's really worth my time to donate. They say that you save a life every time you donate blood, and that all units donated are used. I don't see how this is possible. Surely...

The base units are meters kg and seconds, right? So are some equations meant to use a different set, like cm kg minutes or something. And is it always assumed to be si unless told otherwise?

I guess this is a question about what units to use in any equation. Which ones pair together. If you use 300,000,000 m/s and 1 gram in e=mc^2, you will get 300,000,000, but what unit? Joules? How do you know which to use and which ones pair together?

Homework Statement Show that the force on a moving charged particle F = qv × B from a magnetic field pointing perpendicular to the velocity produces a centripetal force and that this is equivalent to the equation pc = ABρ, where B is the magnetic field strength (in Tesla) and ρ is the radius of...

I always get my foot-lbs and inch lbs confused and don't know if I am applying the correct unit. If I wanted to know how much linear force I can create from a given amount of torque I apply to a thread, I know that I need to find the mechanical advantage of the thread and the torque applied. I...

Please bare with me, I'm not sure how to put in the maths on a forum like this. Ok so i was asked to combine two equations to get a third, this I have done. The equation is M = v squared x r and then the producet of those divided by G. M is the mass of a black hole v squared is the...

The numerical answer is easy to find, but I'm wondering which units are in the answer and how those units are determined. Thanks in advance. (6.63E-34 J×s)(7.09E14 s) - 2.17E-19 J =

Do the units of a wave function vary? i have heard that it just joules. What do you think?

A few years ago, I was reading about a contest open to everyone. The question was something like : if you were on a desert island, with unlimited natural resources, and access to a book with the most accurate values of properties for various natural things (i.e. gravitational acceleration on...

So I understand that converting between CGS and SI units is no easy task when you look at the general form of each equation in electromagnetism, as you can't simply relate the two systems given they have different ways of looking at what is a derived unit and what is fundamental. But once you've...

Hi! I'm doing my master thesis about designing a offshore wind turbine tower for subarctic conditions and I have a major problem with units I'm not much familiarised with Ansys, so I use Ansa as preprocessor and launch the solve in Ansys The problem I have is in units. I'm using Ansys...

So I've been looking at magnetic sensor datasheets and I see the sensitivity is usually listed in units of mV/V/gauss. What does this mean? Let's say I need to sense changes in a magnetic field that usually ranges from about 10 gauss ( 1 mT ) to about 130 gauss ( 13 mT ). And I need to be able...

I have been trying to figure out which formula for the relationship between oscillator strength and transition dipole moment is correct. Wiki had the following formula: http://photonicswiki.org/index.php?title=Transition_Dipole_Moment f = 4.703 \times 10^{29} \bar{v} \mu^{2}_{ge}\,\...

I am talking about length area and volume. As I reason it out in my own mind area (and volume) is based on length and involves 2 random measurements of length that are combined (with multiplication as the device of convention - could any other function be used to work as well and as...

Is kM3/d 1000 m^3 a day or a kilometre^3 a day? I know it should be little m but this is what is written on our gas measuring instrument Are the units kM3/day 1000 cubic metres per day, or a kilometre cubed per day eg 1000x1000x1000 m^3 = 1e9 Thanks

Homework Statement A fan blade is rotating with a constant angular acceleration of +12.0 rad/s2. At what point on the blade, as measured from the axis of rotation, does the magnitude of the tangential acceleration equal that of the acceleration due to gravity? Homework Equations...

Given that heat capacity is a ratio of change of energy over change of temperature, while entropy is a change of energy over absolute temperature... I was wondering if there is any basis for the idea that energy will tend to flow from media having low heat capacity to media having high heat...

I just found a manufacturer that makes a hybrid condensing unit that is roughly the same size as a 5-ton air-cooled one for residential and small building purposes, but it claims to be able to facilitate a 30-ton system. The manufacturer says that it really beats the efficiency of an...

One thing that always puzzled me on the Nerst equation is that you may mix the units of concentration and pressure. This, however, seems to be rather arbitrary. How can using the units of mol/L and atm in the same equation result in accurate results? It seems to be rather arbitrary...

Homework Statement It is estimated that a particular diffuse hydrogen cloud has a particle density of 3e7 cm^-3, and the temperature is 150 K. Calculate Jeans mass. Homework Equations Jeans mass is given by: (5kT/GmewM(H))^(3/2) . (3/4∏p)^(1/2) where k = boltzmanns constant =...

Hi everyone, It's been years since I solved a physics problem for school. Now that I'm back at it I could use some help on this problem: Question "The astonomical unit (AU) is defined as the mean centre to centre distance from Earth to the Sun, namely 1.496 x 10^11 m. The parsec is...

Hi. I'm asked to convert 2 year into the SI Unit seconds: Known: 1 Hr = 3600 s 1 Day = 86400 s So using a calculator... 1 yr = 365*86,400 = 31,536,000 I want to express the answer in scientific notation: Because the lesser number on has 3 significant digits, the scientific...

How can I convert an equation in units where hbar = c = 1 into an equation with hbar and c in SI units? I searched around a bit and wasn't able to find anything (I'm probably not asking the right question). Is there some general way to do it rather than just intuition from having seen the...

Hello there, there have been a lot of conflicts between my physics teachers and university lecturers about the the units for intertia. Some say there aren't any units for inertia, and others say that it's in n/s. However, I don't know who to believe anymore... that's why I'm here :smile...

Homework Statement Assuming that Pressure (P) of a particle is given by P = b - t^2 / ax where t = time, x = position Find the dimension of b/a. Homework Equations The Attempt at a Solution Using dimensional homogenity, I know that b represents time interval.

I have to find the units in $\mathbb{Z}[\sqrt{-7}]$ so take $x,y\in\mathbb{Z}[\sqrt{-7}]$ then x has the form $a+b\sqrt{-7}$ and y has the form $c+d\sqrt{-7}$ for arbitrary x and y. If $(a+b\sqrt{-7})(c+d\sqrt{-7})=1$ then $(a-b\sqrt{-7})(c-d\sqrt{-7})=1$ and so...

Homework Statement Deoxyribonucleic acid (DNA) is thought to be the chemical compound responsible for the process of heredity. A sample of DNA was found to have density 1.10 g/cm3 and its molecular weight was estimated to be 3.04 × 108 g. What is the average volume occupied by one DNA...

I have to find all the units in the ring $F[x]$ where $F$ is a field. Clearly all polynomials of degree 0 are units as they are in the field F. Now suppose $\alpha(x)\beta(x)=1$ which gives $\mbox{deg}(\alpha(x))=-\mbox{deg}(\beta(x))$ which gives $\mbox{deg}(\beta(x)=\mbox{deg}(\alpha(x)=0$...

I have figured out most i needed from my earlier entropy questions but now I'm faced with a different problem... dS=δQ/T that's the formula for the equation. I just did 60 grams of water at 273 K and a room at 298 K so the system is 273 K and the surroundings are 298K Using the forumula for...

When one considers (proper time) ΔΤ2 = Δt2 - Δx2 - Δy2 - Δz2, with c = 1, if t is in seconds, are the units of x,y and z necessarily 3x108 meters?

Homework Statement I'm reading a worked problem in my "Fundamentals-of-Physics" textbook, and it states Homework Equations The Attempt at a Solution I was wondering what are the molecular diameter units which I have emboldened? What does pm stand for? Thank you

Homework Statement Determine the density of fictional planet in SI units from the information Homework Equations Planets mass 1.28x10^22 Kg divided by radius 1.12x10^3Km = 1.14x10^25 Kg/m3 The Attempt at a Solution My answer seems all wrong, the SI unit should be in Kg/m cubed. Is...

Homework Statement I'm currently doing some thermodynamic analysis. I don't know where to put this question, but here goes: I have a system that has two streams entering a condenser, and one leaving. I don't know mostly anything about two of the streams. One stream I have fully defined...

I'm having some difficulty resolving the units (unit conversions will be my great un-doing) for calculation of the Coulomb energy between nuclei. Given that \Delta E = \frac{3e^{2}}{5r} (2Z-1) with the value for r in fermis (~10^-13cm), the elementary charge e in coulombs, and Z is...

Why do astronomers and cosmologists prefer to use the Distance Modulus instead of -- rather than in addition to -- Bly (billion light-years) or Mpc (mega parsecs)? Being a LOG10 it distorts relative distances. You can find Bly plotted on a graph (but not specified), and even in studies comparing...

Do Planck units apply inside of black holes? Are they modified? Or are they irrelevant? If some Planck units remain unchanged and applicable in black holes, which ones would those be?

Firstly, I have a question (irrevelant to the second one) which is: let x,y be in a ring such that xy is a unit. Does this imply that both x and y are units? I know that if one is a unit and the other is a non unit, then the product is a non unit but I was wondering if I could extend that...

Hello, I would like to know, how can I change units showed in axis. I would like to change those relative units (20000, 40000...) to μm. The conversional relation is 50 = 1μm, so instead 20000, 40000 i would like to have 400μm, 800μm. I enclose picture where it should be more clear what I am...

Conduction - Heat Equation - Units Don't Add Up! Hi there I have what I think/hope is a simple question: I've been working on heat inputs and outputs in inertia friction welds and have managed to produce a net power term (W) as a function of time. I now want to use that in the heat...