Zero Definition and 1000 Threads

I'm looking at a velocity chart of the Coma Cluster: And the question occurred to me: why are there so many galaxies that have a zero velocity (relative to the core of the Coma Cluster which is roughly 7,000 km s-1)? At a distance of a Mpc or two you would expect to find galaxies at the peak...

I have a quick question about when we can define the initial velocity to be zero. For example, in projectile motion problems, even though we know that projectile is originally at rest in a cannon, we assign the initial velocity to be some number that we can work with. However, for problems...

why do electric field is zero out side of depletion region?

If $h: \Omega\to \mathbb{R}$ is continuous and $\displaystyle \int\limits_{B(x_0,r)}h(x)\, dx=0$, for all $B(x_0,r)\subseteq \Omega$, then $h(x)=0, \, \forall x\in \Omega.$Hello MHB, is an problem that I don't solve :(. Help me please or any hints :). Thanks.

I saw a video by a physics writer who said that the beginning of the universe was like digging a hole: the hole and the pile of dirt cancel each other out. This of course means that the ground, so to speak, before the digging was zero. But where is the "hole" once the universe began? I asked...

1) While running with a constant velocity ; how do we consume energy? : Only due to vertical movement of our bodies, right? 2) When driving a car in a constant velocity; how this car could consume energy? It does not move upright-downright (in a very straight road).

What is the effect in quantum if Planck constant is zero? Here are some points that I could think of: if Planck constant is zero, the Heisenberg Uncertainty Principles will become zero, therefore either momentum or position of a particle can be known exactly. if Planck constant is zero, both...

Can someone correct my understanding on electromagnetic waves please; I've clearly got the wrong end of a stick somewhere, but can't figure out where my misunderstanding is! Thanks. If I draw a classic EM wave with the electric field on the up and down axis and the magnetic field at right...

I've just started self-studying measure theory by reading Pugh's Mathematical Analysis. I'm trying to understand his argument for why the exclusion of a zero set does not change the outer measure: $m^*(E\setminus Z)=m^*(E)$: (Pugh's arugment): Let $Z$ be a zero set, $E\subseteq\mathbb{R}$, and...

Homework Statement I'm trying to show that ##\Sigma_j(\vec a_j \cdot \vec B)=\vec B\cdot\Sigma_j(\vec a_j)## (I need this to be true to derive some angular momentum properties.) 2. The attempt at a solution Let's say that in some coordinate system we can express the vectors as ##\vec...

Suppose you have a free election and you make a measurement of its position r_0 at time t = 0. You then wait some time t required for the wave function to evolve out of its collapsed eigenstate. The electron now supposedly has a wave function expanding to infinity in all directions, albeit with...

Homework Statement Hi, with regards to the negative zero error , do we read the vernier scale from the left or from the right? In this case, should it be -0.04cm or -0.06cm? Thank you !

Assuming that the expectation that all matter and energy are quantized is correct, I'm making a further assumption that "random" means something like, "hypothetically predictable, but only by means at least possibly impractical on any permanent or general basis whatsoever, such as enumeration...

Homework Statement why the object will fall of when the normal reaction force is less than zero ? P/s : the normal reaction force is in downward direction... How if if the normal reaction force is less than zero ? the normal reaction is in upward direction ? Homework EquationsThe Attempt at a...

Hi, What is the physical meaning of zero probability of finding a particle in the square of the Quantum SHO wave function? the particle is supposed to oscillate about the equilibrium position, how would it go from an end point to the other end point without passing by certain points? Could the...

Hello I have a quarter wave plate for 550 nm but i can't determine which it is a zero quarter wave plate or multiple. How can I find m in this formula : delta phase =m*2 Pi +Pi/2 ? Thank you.

Greetings , Is the zero potential level ( not the ground state) considered as an excited state ? and why the ground state isn't an excited state ?

I have read that the elementary particles of the Standard Model have dimensions 0. Is this the case or not? I have read on this site relevant answers to similar questions, but have not found them to be very clear. If it is the case, surely much of quantum weirdness is thereby explained: after...

Hi, For SU(2) I can have that all Noether charges commute with one of the charges as one of the generators of the Lie algebra is the identity. Can somebody explain me how this is related to the properties of SU(2)? Charges can be considered to be generators of the transformation. So if this...

Homework Statement Homework Equations Dirac equation: $$(\gamma ^{\mu}\rho_{\mu}-mc)\psi=0$$ The Attempt at a Solution If we multiply out the Dirac equation by inserting all it's components we get: which if I've multiplied it correctly gives $$ \begin{bmatrix} \frac{E}{c}-mc\\ 0 \\...

I have some questions related to how a discrete control system is designed. One method is to design the controller in the continuous time domain, arriving at a transfer function (in the s-domain). After that, a transfer function for the ADC system must be taken into consideration. I will suppose...

Say we are talking about an ideal gas. According to ideal gas law (PV=nRT), assuming the gas is now at absolute zero, if we further decrease the pressure of the environment, while keeping the container volume constant, will the gas goes under absolute zero? I wasn't an expert in Physics so...

Is it possible to achieve absolute zero?

When is the rate of change of momentum equals zero ?

Homework Statement A Michelson interferometer is illuminated with a laser with a wavelength of 514.5nm. A Haidinger fringe pattern is photographed with a lens of focal length 55mm. The diameter of the two adjacent circular fringes in the image are 1.53mm and 2.62mm. How far would the mirror...

Is zero discrete?

I've been dealing with the concept of moment this whole year, in statics/dynamics but I've never really completely understood it, just rather memorized it. What I think moment is: If some point on a body has moment, then this means it wants to rotate. So moment is essentially what causes...

A is invertible... How give me the proper explanation...

Basic question, I think, but I'm not sure. It is a step in a demonstration, so it would be nice if it were true. True or false? Why? If A is a real, symmetric, nonsingular matrix, then xTAx≠0 for x≠0.

Hi, my question is the title, if Ricci tensor equals zero implies flat space? Thanks for your help

Homework Statement Demonstrate that the expectation value of momentum (p) for the wave function: ψ(x)∝e^(-γx) when x>0, ψ(x)=0 when x<0. Hint: Pay special attention to the discontinuity at x=0.[/B] Homework Equations <p>=<ψ|p|ψ>=∫dxψ*(x)[-iħ∂/∂x]ψ(x) from -∞ to ∞. [/B]The Attempt at a...

I have an inclined pulley with inclination 30°. There is mass A on top of it equals 2 kg. And over a frictionless pulley there is a mass B with weight 0,83 kg. The text says that the coefficient of friction is 0,18 between mass A and the incline. I need to know the acceleration. and I also have...

I am designing a Pan and tilt drive for with stepper motor as prime mover. We need a zero backlash worm drive to transmit 70 Nm. motor torque is 1 Nm. What are the options.. position accuracy is 0.1 deg. thanks

Can anyone explain why sum of Ft has been set to be = 0? The slope is smooth so no frictional forces act but by setting it to 0 they are neglecting the component of the weight along the slope? Having said that, this is a curved slope and not a straight one so does the component of the weight...

Hello, Let ##g_{jk}## be a metric tensor; is it possible for some ##i## that ##g_{ii}=0##, i.e. one or more diagonal elements are equal to zero? What would be the geometrical/ topological meaning of this?

Hello, I am analysing hydrology data and curve fitting to check the best probability distribution among 8 candidate distribution. (2 and 3 parameter distributions) The selection is based on the lowest AIC value. While doing my calculation in excel, how is it suggested to treat very low (approx...

Homework Statement Please see the attached file if my inline insertion does not work. Homework Equations ##det(A)=det(A^T)##[/B]The Attempt at a Solution Since a matrix has a determinant of zero only when it's columns are linearly dependent, we look for a set of points [x1 x2] such that...

The hint I found in http://math.stackexchange.com/questions/448207/how-to-prove-that-lim-limits-x-to0-frac-tan-xx-1#answer-448210 limx→0(tan(x) / x)= limx→0( (tan(x)−0) / (x−0)) = limx→0 ( (tan(x)−tan(0) ) / (x−0) )=⋯ Then, I don't know how to continue it.. What identity is used ? I don't see...

In the plot command below x=1:5:100 plot(x,y,x,0) one plot is noncontinuous zero plot. How can I plot a continuous zero one?

The Standard Model formula for the cross-section of ##e^+e^-\rightarrow\mu^+\mu^-## is made up of 3 components: QED interactions, weak interactions, and electroweak interference. I understand the behaviour of the QED part, and the resonance that occurs in the weak part at ##\sqrt{s}=M_Z##, but...

Hi! At the moment I'm studying rigid body motion, more specifically, the gyrocompass. As you can see in the attached picture (Introduction to Mechanics -Kleppner-Kolenkow-Chap.7), the gyrocompass rotates about the z axis and the spin angular momentum is reoriented towards the z axis, creating a...

Homework Statement I am making an old exam of a particle physics course, and i know how to calculate the cross section for example for bhabha or moller scattering. now one of the questions on the old exam is: Explain why e-+ e+ -> γ is zero, but i am not sure why this is, can someone explain...

Thanks!

Homework Statement Integral of ∫1/x^2 (or ∫x^-2) between 1 and 0.The Attempt at a Solution I can integrate it no problem to give me -1/x or x^-1, but when I put it between the limits of 1 and 0 I get ∞-1 which is just ∞. Is this right or do I need to use L'Hopital's rule. If so, how? I'm...

Homework Statement I have the circuit in the picture below, and using KCL and KVL I found that the voltage over the 80k resistor is 0. However, I don't understand why this is correct. Can someone explain why there is no current through it? Homework Equations None The Attempt at a Solution I...

This is example 27.2 in my textbook. I have the answer, but it doesn't make sense to me. I understand that if electric field is tangent to the surface at all points than flux is zero. Why, though, does my textbook assume that the ends of the cylinder don't have field lines extending upwards and...

Suppose we wish to represent ##f(x)## as a power series: $$f(x) = \sum_{k=0}^{∞} a_k x^k = a_0 x^0 + a_1 x + a_2 x^2 + ...$$ How is it that ##f(0) = a_0## if ##x^0 = 1## only for nonzero ##x##?

I have a bit of problem with zero eigenvectors and zero eigenvalues. On one hand, there seems to be nothing in the definition that forbids them, and they even seem necessary to allow because an eigenvalue can serve as a measurement and zero can be a measurement, and if there is a zero eigenvalue...

Homework Statement A -10.0 nC point charge and a +20.0 nC point charge are 15.0 cm apart on the x-axis. a. What is the electric potential at the point on the x-axis where the electric field is zero? b. What is the magnitude of the electric field at the point on the x-axis, between the charges...

In one dimension, the acceleration of a particle can be expressed as: $$a = \frac{dv}{dt} = \frac{dx}{dt} \frac{dv}{dx} = v \frac{dv}{dx}$$ Does this equation imply that if ##v = 0## then ##a = 0##? EDIT: I think I figured out the source of my confusion. This equation is a differential equation...