Scale Definition and 721 Threads

Let me start by saying my understanding of logarithms is relatively limited, with that out of the way on to my question. The question I have is in a situation where you have 2 items that are inversely related and both have a starting point of 100%. How would you calculate the point where...

I'm having trouble understanding the part in the Friedman equation where a'/a. I can't figure out why it's the derivative of a over a itself. If someone could give me some sort of analogy to something I already understand that would help. I'm pretty sure a is the rate at which the universe...

the link is worth having a look at to illustrate the scale of our universe http://www.htwins.net/scale2/

Hi all, I have a rather naive question about the fine structure constant and the relationship between its value and the energy scale involved. I understand the idea of the a charge being 'screened' by vacuum polarization (i.e., electron-position pairs popping in and out of existence), and...

Hello physicists! I'm hoping you can help me with a question I'm pondering for a book. At what acceleration could a 4 km^2 solar sail move a 1 metric megaton starship? Assume we're using the solar radiation from the Sol system as our force and that the solar sail in questions is as low mass...

Hi, how can i change x and y-axis scale to make sure that x and y-axis are on the same scale in matlab? my x-axis is from 0 80 but the y-axis is from -3 to 5, so in plot the axis are not the same but i want to have same scale on both axis. Thank you.

I'm looking to put motors into a scale model plane and was just wondering whether the motors I've picked will be ok and what sort of supply voltage I would need. I'm going to use 4 of these.7 Specs: Operating Voltage: 3.7V Diameter: 7.0mm Length: 25.5mm Output Shaft Diameter...

Assuming there is a mass on a scale, and they move with the same velocity. I know mass increases for a moving object, but the scale's mass will also increase. So would the scale read any more than if they were both at rest?

Homework Statement A man with a mass of 100kg stands on a scale with a sack of potatoes weighing 20kg. He throws the sack straight up. At the instant before he releases the sack, what does the scale read, in kg?Homework Equations n/a The Attempt at a Solution I assumed that because the sack...

If we know that the temperature of photons was apprx. 3000 K at recombination and the temperature of the CMB is apprx. 2.725 K today, how can we extrapolate the value of the scale factor at recombination? I know that recombination happens at a matter-dominated era, such that the density goes...

Lets take that magical number 1 with 100 zeroes at the end known as google and see what we can put it into. My challenge/ curiosity for the ones who love calculations is this: Not counting for gravity, and using any temperature you choose, how large would a cube of pure lead have to be to...

I will get right to the point, a grower of super hot peppers in Florida has almost 10,000 plants of twenty eight varieties in pots, 3 - 10 gallon pots, forced drip irrigated. Many plants are near fully grown, they are staked in their pots to hold them up as needed, and all are under a...

Looking at the Friedmann equation H^2=\left[\frac{\dot{a}}{a}\right]^2=\frac{8\pi G\rho}{3}-\frac{kc^2}{a^2} and considering positive curvature, then for the limit where the second term dominates, we're left with \left[\frac{\dot{a}}{a}\right]^2=-\frac{kc^2}{a^2} This implies a complex...

Hi everybody, I've searched all the internet but I can't find the answer to my question. Which are times of decoherence for different physical realization of a qubit? Like, if I use photons, or spin electron, or nuclei, or ion trap, to encode a qubit, which are times of decoherence for each...

We all know the trick of holding water in a drinking straw by holding your thumb over the top creating a vacuum I know its also to do with air pressure below. I managed this on a bigger scale using a 2inch pipe, a water pump and a valve i could close at the top of the pipe to replicate the...

In the context of Friedmann's time, 1922, how did he know to make the metric scale factor, a, a function of time when Hubble's redshifts were not yet published? I understand that he took the assumption that the universe is homogenous and isotropic, but does that naturally imply that the universe...

I have some experimental data of a simple RC circuit, which I measured in fixed time intervals the current through an microamperimeter, and now I need to make an i(t) × t graph, with the vertical axis on a logarithmic scale (so my points fall into a 'straight' line), and then I need to find the...

Since the Euler-Lagrange equation is homogeneous, the equation of motion of a system of particles or a field is independent of the scale of the Lagrangian. That is, we can multiply the Lagrangian by any constant and arrive at the same equation of motion. But does the scale of Lagrangian or...

Homework Statement hi i have the folowing data i would like to plot in matlab plotERRLW = 0.0466 0.0111 0.0074 0.0046 NX = 50 500 1000 2000 i am using a logarithmic graph to gain a straight line, if i wished to find the gradient of the line...

I often hear something to the extent of, 1) "despite cosmological expansion, small-bound objects do not expand." and further, 2) "things like galaxies will aways remain bound, and will not expand." Pertaining to 1) Because cosmological expansion is a coordinate property, don't small scale...

Say that an object is placed on a scale and it gives a reading. Does that number represent the object's weight (w = mg) or mass (just m)? I'm a bit confused because my physics teacher told me that it is measuring its mass...is this correct? Many thanks.

Homework Statement An object is hung from a spring scale attached to the ceiling of an elevator. The scale reads 65 N when the elevator is standing still. What is the reading of the scale when the elevator is moving upward with a speed of 7.6 m/s and decelerating at 2.4 m/s^2? Homework...

So I've been trying to figure out how to find the surface area Jacobians in spherical coordinates (I know how to use it to find the volume Jacobian). Using the divergence theorem I was able to find these Jacobians top-down, however, I am unsure to how one would derive them in the first place. I...

I know even molecules can be used and the result still emerges. What is the density of [pick a type] of atoms or molecules when the experiment stops working? Also, as you increase the density of whatever you're using, does the result get less and less like what you get when you use photons...

Weight on a Scale Down an Incline vs. True Weight Homework Statement Judy fastened a set of bathroom spring scales to a wedge shaped skate board as shown and coasted freely down a 30 degree slope. The wheels were well oiled and the platform supporting the scales was horizontal. What...

Hey guys, I am thinking about world at small scale and world at larger scale. Why world is more chaos at smaller scale and why it is more smooth and uniform in larger scale?

Hi I am reading about the force of a coherent EM-beam acting upon an atom, and I have a question in this regard. It is regarding the explanation on page 150 of this book, starting from "The geometric approximation of atom optics is valid when"...

Why aren't we still able to create/alter organisms for energy and food production, since we can easily sequence and cut and paste DNA?

Hello I am newto this and maybe it is an easy answer. Here is my question. When I travel in my car at 60 mph. I travel as a whole with the car at 60 mph. But at an atomic size and scale don't the atoms that make up everything really travel faster? Because at that scale wouldn't it be much farther?

Not sure if this is old, but it's an interesting little animation! http://scaleofuniverse.com/

Hello everyone, I have a bit of an issue regarding scaling of an expression. So, the scenario is as follows. I have a confidence value that can be associated with the solution given by an optimization routine and it is as follows: C = exp(-A)/(exp(-A) + exp(-B)) where A, B and C are...

This is a zoom-in, zoom-out animation that explores various objects from the very small (plank length) to the very large (Sloan Great Wall). Judging from the descriptions, I think it's intended for children. http://images.4channel.org/f/src/589217_scale_of_universe_enhanced.swf I lold...

Dear all, I am looking for literature describing the application of large scale sonication. Something like sending ultrasound through the ground. I know it has been done, but I was unable to find anything about it. Can anybody provide some suggestion? Many thanks

An absolutely amazing animation: http://images.4channel.org/f/src/589217_scale_of_universe_enhanced.swf Link broken[/color] http://www.newgrounds.com/portal/view/589217

One of the foundations of General Relativity is diffeomorphism invariance - the fact that the laws of physics are invariant under smooth coordinate transformations, and thus the laws must involve tensors. My question is, why doesn't this imply scale invariance; after all, isn't a change of...

A rectangular park has an area of five hectares (1 hectare = 10,000 meter square) The dimensions of the park on a map are 5 cm * 4 cm What is the scale of the map?

can many world interpretation be valid for large scale collapses that brings out a single reality?

My teachers in school use to say. "the dumbest question is the one not asked", but I might just break that rule with this one. :smile: Here goes... I've been reading a lot of articles today on light travel, the Higgs field, and other fascinating stuff. Lastly, I was just reading an article...

Homework Statement Add each set of vectors by using the scale diagram C=28km 20 degrees north of east; D=34 km 30 degrees west of north Homework Equations The Attempt at a Solution Attempted to create a triangle with a right angle; then Pythagorean

Hello, I've been toying with the idea of making a cheap dynomometer for small electric motors, but one of the obstacles I'm encountering is finding a cheap load cell. The best I've done so far is a $75 sensor from Omega, which still requires conditioning. Then it occurred to me that you can...

How can relativistic length contraction be measured at the quantum scale? Since a Planck length by definition cannot be divided, how can something that is 1 Planck length, traveling near the speed of light, contract with respect to an observer? In other words, how can an observer possibly...

I sent a paper in for peer review to the journal "General Relativity and Gravitation" 30/10 2011. On 12/11 2011 they sent it out for peer review. Then 5/12 2011 they sent it out for peer review again, obviously one of the referees could not make up his mind or something so they sent it to a...

I've read in several places that MOSFETs scale, while BJTs and JFETs do not. I'm curious how a MOSFET scales better, and what is meant by "better", as in do they lose frequency response, power capability, etc. more so than MOSFETs when scaled? Obviously to me a clue is that both a BJT and...

What is the current value of the scale factor(R₀)? a= R(t)/R₀ Give me the number.

Quantum Gravity only becomes a problem when we probe below the Planck scale. This is because we don't know what occurs inside a singularity in a Black Hole or in the initial condition of the Big Bang when the universe was supposed to be in Planck density. The Planck scale is also the origin of...

Homework Statement A trailer carrying a boat is supported by a scale which initially reads 48kg. The boat is moved 0.15m further back on the trailer. The scale now reads 37kg. What is the mass of the boat? Homework Equations torque = F(perpendicular) * d For...

Homework Statement Hi, I'm asking the usual "what formula gives me these results" question, but with a twist; I'm attempting to make a "virtual" analogue multimeter that replicates a physical piece of equipment, for training purposes. The idea is that a random MegaOhm value will be generated...

Hi I am new to this site and I really need help I missed this class and of course my book doesn't have this formula so if anyone could tell me it that would be great. The temperature of the universe is now 2.725 K, and its scale size is 100 Mly. How hot was the universe when its length...

What are the reasons for scientists believing the Planck scale is the smallest unit of length? I have been hearing a lot of this length scale recently and i know we can't even do expiremental research at these small of levels. I'm wondering where they got the idea that strings [from string...

Hello, I am reading this paper about quantum gravity, trying and failing to follow along in the derivation of this, eq (204) p. 72, expression for the scale factor: a(t) = a_1 \left( 1 + \frac 3 2 ( 1 + \omega ) H_1 (t - t_1) \right)^{\frac 2 {3(1+\omega)}} (I'm not sure what the...