Scale Definition and 743 Threads

As a teacher, I am trying to help students understand the scale of the universe. Using the analogy of sand as stars, and based on the average size of sand as .5mm across, I worked out... 1. The number of stars is greater than the grains of sand on all the beaches of the world (allowing...

I have two questions that I think are analogous (tell me if they are not). 1. If I have a spring scale and apply 50 pounds of force to one side and 40 pounds to the other, what would it read and why? (I think it will read 45 pounds because that is what the tension would be if it were a rope)...

I have a psychological testing instrument that produces an ordinal measure (0, 1, 2, 3, 4, 5). I want to change this to a ratio scale with range 0 to 5. The instrument is designed so the first 5 questions are very easy (Level 1), the next 5 questions are harder (Level 2), the next set is...

why the topological term in gauge theory, ε_{\mu\nu ρσ}F^{\mu \nu} F^{ρσ} ,is scale-independent?

I know this is a very common question but I've been seaching in forums all the time and couldn't find a clear answer. So quantum physics say that we can't actually "touch" anything because of our atoms( we're all made of atoms and they repel each other). correct me if I am wrong,please.. atoms...

Hi, the following two views appear inconsistent to me: In the infinite perfectly homogeneous universe: a) the net force of gravity is zero everywhere, so no energy is being exchanged and no particle is pulled in any direction whatsoever. b) the net force of gravity within a spherical...

I am Post Graduate in Physics and working as a researcher in Non Destructive testing. I have heard about multi-scale simulations and its applications to material modelling. Iam intersted in learning mutiscale simulations for materials modelling. can anyone provide me links that would let me...

For the past week or so, me and a buddie have been trying to figure out how to make a mini-hoverboard kind of this, now it doesn't even have to look like a hoverboard we just want it to be able to get off the ground with 2 fans. What we were going to order was all this stuff...

A homogeneous and isotropic Universe is described by the FLRW metric: ds^2 = c^2dt^2 + a^2(t)\ d\Sigma^2, where ##a(t)## is the scale factor and ##d\Sigma## is an interval of uniformly curved co-ordinate 3-space which is independent of cosmic time ##t##. If we set ##dt=0## then we find that...

Can anyone recommend some usufull links,pdf,... for information on large scale structure? I want to fully understand how in the cold dark matter model the the hierarchical formation of matter occurs and the role of the initial perturbations in the evolution of the universe. Thank you.

I remember hearing this, but not sure if it's true.

I have a floor plan where 1/8 inch = 1 ft. The architect labeled the square footage in each room, but not the measurements from wall to wall, so I measured with a ruler and now I'm having a difficult time converting from inches to feet. I'll use one rectangular room as an example. My...

Hello All, In Carroll's there is a brief introduction to a dynamical dark energy in which the equation of motion for slowly rolling scalar field is discussed. Then to give an idea about the mass scale of this field it is compared to the Hubble constant, saying that it has an energy of...

Hi there, I think this is in the right section if not please inform me and move my thread. I want to design and build a UAV in a copter format whether it be quad, hexa, octa, ect. I want to make a modeling software so that I can design the most efficient blade/motor for my specific needs. I am a...

I wrote it in another thread but it got lost in the middle of the other comments. So, here goes my doubt: In some places I am reading things like the following: For example here: http://motls.blogspot.com.ar/2014/03/bicep2-primordial-gravitational-waves.html#more Where in the whole...

Hi there, I am trying to solve a structural mechanics problem. I am doing so by two methods. On one hand, I am using a F.E.A software (ANSYS) to get me the solutions. At the same time I am solving the problem analytically. The issue is that ANSYS is solving the problem using a diferent theory...

what is the physical meaning -and nature- of heat in the molecular scale? how can molecules emit heat in forms other than EM radiation? i used to think of thermal energy of matter as the vibrational (kinetic) energy of the atoms/molecules that make up the matter. yesterday i was reading about...

Hello, I am looking for a physics/engineering project that is doable over a couple of weeks and has a bit of wow factor. Building a trebuchet would be a good example but I would like to do something else. Any ideas? Thanks.

Hi, I'm a Mech. Eng., so forgive my ignorance to power electronics, but I'm hoping someone can explain this to me. Considering the scenario where a small gas turbine (< 500 kW) drives a generator to provide power to the power grid. The power output of the turbine will not be constant...

hello all. here are link lengths Link 1=177.8, Link 2=228.6, Link 3=76.2, Link 4= 203.2 . I don't know how I can choose a convenient scale for these links.Do you have any idea? For example is it a good approch to choose 1 cm for 50 mm.to what centimeters can I roll the numbers. Link ratios to...

I'm trying to make a fixture measure how much force it takes to deform various items. However, digital force gauges costs upwards from while simple scales don't cost much at all. What's the difference between using a fancy force gauge and placing a digital scale underneath an item that's...

Greetings PFers, I'm working on a project where I need to focus powdered that is being blown through a tube. I would like to discuss the option of using acoustic focusing to guide the particles to the axis of the tube to prevent the particles from contacting the tube inside diameter. There...

Homework Statement At an outdoor market, a bunch of bananas is set on a spring scale to measure the weight. The spring sets the full bunch of bananas into vertical oscillatory motion, which is harmonic with an amplitude 0.14 m. The maximum speed of the bananas is observed to be 2 m/s. What is...

Homework Statement A mass of 2kg is sitting on a dial scale balance on the floor of a lift. What is the reading on the balance when the lift is moving downward with acceleration of 3 m/s2 Homework Equations F = ma F = mg where g = 10 m/s2 in this question. The Attempt at a...

Hubble Sees Infant Galaxies at the Edge of the Universe http://www.slate.com/blogs/bad_astronomy/2014/01/09/distant_galaxies_hubble_image_of_galaxies_at_the_universe_s_edge.html

I have a classroom full of Ohaus cent-o-gram model 311. Most work fine, but a few I can't calibrate to 0. I've used the calibration screw, but even maxed out it isn't enough. I could always place a couple of pennies under the tray, but there's got to be some way to do a course adjustment...

I recently came across this paper http://arxiv.org/abs/physics/0504110v2 by Oas that is a semi-rant about how pedagogically evil relativistic mass is. He gives the following sample question: From the context, it appears that the students are expected to have little or no background in...

The generic FLRW metric is dS^2 = a^2.(dx^2 + dy^2) - (c.dt)^2. Is it equivalent to the metric dS^2 = (dx^2 + dy^2) - (c.dt/a)^2 with the scale factor in the denominator of the time dimension? (I suppressed one dimension just for simplicity). Thanks for the help.

Hi everyone, long time lurker, first time poster. I've just begun a phd which involves nanoribbons (a small strip of a 2D material connected at either end to a larger 'bulk' section of the same 2D material). A question has occurred to me. These nanoribbons look a lot like a piece of string...

Homework Statement I just have a general question regarding scales and forces. I came across a question that when a boy jumps on his scale, the weight shown is actually greater than his actual weight. I have a hard time picturing this because when he jumps, he isn't actually on the scale...

if thermo couple ammeter full scale deflection is 10 Amp, for 1/5 th scale what is the Reading?

Hi I have been reading that we "believe" that new physics must be O(~1 TeV) and not higher and I am trying unsuccessfully to find some ref for this. What I do understand is that if we we assume the Standard Model is valid for scales Q<Λ , where Λ∼O(1TeV).At one-loop level, we get large...

Hello, I'm in the process of calibrating a thermometer/datalogger (Omega DP470) that uses a thermocouple type T (-200-350 deg. C range), and I need a DC voltage source that can feed a steady voltage of 39.000 mV. I believe at this point I can either purchase a precision voltage source that...

I want to kindly ask about opinion what will be if : a) rocket's speed < gravitation b) rocket's speed > gravitation ************************************************************ Earth ----- Rocket[W]m >>> constant V [W]- scale can measure kg [m]- person mass Scale is showing Qearth +...

http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/weighing-buoyancy/So I was wondering if both the scales would show the same weight value? (the scales are marked black in the picture) The object on the left is a pyramid and the object on the right is a cube. They are both...

Hopefully this is in the right sub-forum. Anyway, we all know the Planck length placed a limit on how small something can be and still make physical sense. Is there a macro version of this? Is it possible that the universe/multiverse, or some other macro object, can only be so big before it...

In Morse & Feshbach (P512 - 514) they show how 10 different orthogonal coordinate systems (mentioned on this page) are derivable from the confocal ellipsoidal coordinate system $(\eta,\mu,\nu)$ by trivial little substitutions, derivable in the sense that we can get explicit expressions for our...

Homework Statement On a Temperature scale, the ice point is 25.6°I and the steam point is 155°I. If the temperature reads 66.6°I what is the equivalent in °C? The Attempt at a Solution 25.6°I = 0°C 155°I = 100°C 1°I = 5/647 of the interval between boiling and freezing. 1C° =...

I have performed a small experiment to obtain the VI characteristics of a semiconductor diode using ANALOG DISCOVERY circuit design kit. I have connected the arbitrary waveform generator (function generator) to a series combination of a 1N4007 diode and a 1 kilo ohm resistor. To obtain the...

Hi, Are Einstein's field equations without the cosmological constant scale invariant? If so does the addition of the cosmological constant break the scale invariance? John

Homework Statement Hello all, I saw a picture today of a physics problem which is really a head scratcher in my opinion. See the attached photo. You have two columns of water on a scale. In the left column, you have a ping pong ball, attached by a string to the bottom of the container...

I'm struggling to understand the implications and origins of the 2nd law. Entropy is such a slippery subject. Wikipedia has many many definitions of entropy. I've been studying Professor Susskind physics lectures, so I'm most interested in his favorite definition: that information is...

This is the first time I post anything here, so, if I am doing anything wrong about the rules (it is possible that I didn't correctly understand a topic or two), please let me know. This one is a somewhat classic problem of damping, and I can't understand the basic concepts, so I tried to do my...

Iron ball hanging from a scale and suspended... 1. Iron ball hanging from a scale and suspended in a glass of water filled to the rim, what happens to the reading of the scale, volume of water, and weight of the glass of water? 2. FB = weight of removed water by the ball 3. there's a FB...

Iron ball hanging from a scale and suspended... Iron ball hanging from a scale and suspended in a glass of water filled to the rim, what happens to the reading of the scale, volume of water, and weight of the glass of water? The attempt at a solution: there's an FB that's equal to the...

http://scaleofuniverse.com/ Have a play with it, you can mute the sound in the top right. It's such a cool app.

Hello everybody, I have a short question about the renormalization scale. For dimensional regularization we introduce a scale μ with mass dimension to preserve the correct mass-dimension for the coupling and so on so that it is independent of the value of d = 4-2ε. But why can that μ have any...

So, I was wondering if a conducting loop was placed in orbit around the Earth would it be able to generate a current?

Homework Statement If we multiply all of the design dimensions by a scaling factor f, it's volume and mass will be multiplied by f^3. (a) By what factor will its moment of inertia be multiplied? (b) And if a 1/48 scale model has a rotational kinetic energy of 2.5J, what will be the kinetic...

I have always understood Planck time as being the the smallest amount of time that has any physical significance and the Planck scale as being the region where space and time collapse on each other and all of our mathematics fail. Why are these seemingly magic numbers the end all be all of...