Physical Definition and 1000 Threads

From the equations of equilibrium "σy+(∂σy/∂y)*(lower case delta y)" is the force acting along y direction. can anybody explain the physical meaning of the second part of the force where we multiply delta and del?

Many people out there today seem to think that we'll soon have computers powerful enough to simulate the physical world well enough that we'll be able to upload ourselves and live in such a simulation. People really seem to think a Matrix situation is possible. Some, like Nick Bostrom, have...

I know the definition of the Poisson bracket and how to derive elementary results from it, but I'm struggling to understand intuitively what they are describing physically? For example, the Poisson bracket between position q_{i} and momentum coordinates p_{j} is given by \lbrace...

Homework Statement A metal rod of length 'L' and mass 'm' is pivoted at one end. A thin disk of mass 'M' and radius 'R' (<L) is attached at its centre to the free end of the rod. Consider two ways the disc is attached : Case A: The disc is not free to rotate about its centre of mass, the...

I was wondering what the physical insight is of integrating a product of two functions. When we do that for a Fourier transform, we decompose a function into its constituent frequencies, and that's because the exponential with an imaginary x in the transform can be seen as a weighting function...

I know this may not be a typical question for the Physics board. I am a MA Design student working on a project to illustrate experiments on speculative/fictional physical events. My final work will consist of strongly simplified staged experiment lab situations and should touch on the imaginary...

Here is one of the KdV form u_t + u_x + uu_x + u_{xxx} = 0 Where u is elevation, x is spatial variable, and t is time variable. The first two terms describe the linear water wave, the third term represent the nonlinear effect, and the last term is the dispersion. From what i understand, the...

Here is one of the KdV form u_t + u_x + uu_x + u_{xxx} = 0 Where u is elevation, x is spatial variable, and t is time variable. The first two terms describe the linear water wave, the third term represent the nonlinear effect, and the last term is the dispersion. From what i understand, the...

I noticed that famous theories have a non physical part in them : Newtonian instantaneous forces Quantum particles going faster than the speed of light in schroedinger mechanics. This contradicts the maybe only physical theory that exists : general relativity. I thought the following...

Whats the circumtances which physics rules collapse and don't work.Theres any explanation it to use mathematics. Here I don't mean singularity things.I know in singularity physics rules collapse I want to talk more generally.

Hi all, I am trying to obtain an empirical equation/model having 2 inputs (frequency and S11) and one output (a physical parameter) I have done various simulations using CST of the System and now I am trying to relate S11 and frequency to a physical parameter. Any suggestions of how I should go...

Homework Statement What is the difference between a dimensional physical constant and dimensionless physical constant? Homework EquationsThe Attempt at a Solution

Hello PF! I have a simple question on energy balances. Suppose you have an isothermal reactor where you want to have an exothermic reaction happening at 450 °C. The simplified energy balance for the reactor is Q = ΔH. Supposing ΔH = -150 kcal, then Q = -150 kcal. Does this mean that, a) in order...

Let me first give a quick sketch of how Noether's theorem was stated in class and then explain what is not very clear to me. Consider for simplicity the Lagrangian of a single coordinate ##L(q,\dot{q},t)##. Now, if there exists a variation of the coordinate ##\delta q## for which at any time...

The Thomas-Fermi wavevector relates to the damping of an electric field caused by build up of carriers around an impurity (screening). But I can't understand it's physical meaning. Wiki states "Thomas–Fermi screening is the limit of the Lindhard formula when the wavevector (the reciprocal of...

I'm having trouble with with understanding what this is, our text, Astronomy: a physical Perspective by Kutner, uses R(t). I understand r(t) is the distance between two objects at a point in time, but what is the scale factor big R(t)?

This is probably pretty basic but I've never actually seen an explanation of how exactly the sine wave relates to the physical waves it is so commonly used to represent. Could it be imagined as like the periodic thumping of a speaker where the peak of the sine graph represents maximum air...

Hey everyone. I'm sorry if I'm posting something irrelevant here. I really don't know where to ask this question but this hit me while learning Computing Principles (It's my first day in college). I'm one who is interested in physics too. Hence, I got a little confused about the term...

For a physical singularity I think it is sufficient that anyone scalar quantity blows up, Why is it not a necessary condition that all blow up? For a curvature singularity am I correct in thinking that it is a sufficient condition to find a coordinate system in which the metric coefficient no...

I study in high school, but I know a fair amount of math (differential, integral, and vector calc., differential equations, linear algebra, etc.) Would you recommend this book if I want to pursue higher levels of math such as PDE's and Tensors and so on? Does this book explain things clearly...

I apologize if this seems ignorant, but I am at a loss and I need some assistance. I recently built a small vacuum PVD system (Ion source, argon, target material, substrate cradle, etc.) and was showing it to a colleague when it was noticed that my system was unbiased. It actually didn't occur...

Homework Statement I am just a little bit confused. I have a question that is asking me to explain what the physical significance of volumetric flux is. Homework Equations I am not sure that this problem requires any equations! The Attempt at a Solution I know that the flux corresponds to...

I am interested in how phonon softening would lead to changes in a crystals elastic properties but I don't understand what actually is the consequence of this. What would be affected by a reduction in energy to phonons in a crystal? My best guess would be a reduction in energy to phonons causes...

Homework Statement A weather balloon is filled with Helium gas and released from the ground. It goes up 18km and achieves a diameter of 15m. Determine if the following values are greater than zero, less than zero, or equal to zero: ΔV, ΔP, ΔT, ΔU, ΔH, Ssys, surr, Stot Homework Equations ΔU =...

Hi I was wondering if there any observations that have only been described using the Riemann Zeta function? What would it mean in physics to assign a divergent series a finite value? Thank you Edit Sorry I overlooked a thread just posted that asked about this so this might need to be deleted.

Homework Statement A rectangular 4 x 8 foot sheet of plywood is fixed to a sled which moves on a track. The face of the plywood is perpendicular to the direction of the track. The sled is pushed a distance of 3 inches. What is the volume of air swept out during this motion. Homework Equations...

Hopefully I can word this correctly. Consider viewing S11 of a short on a smith chart. It starts at the left and moves clockwise around the edge. If you then add a small length of line between the reference plane and the short, the phase angle wraps further around the outside in the clockwise...

Hi dear forum members, I'm an undergrad. physics student(freshmen),i've learned that Galilei found g.t^2=s formula(a free falling object's position function with respect to time)without using physical foundations,by using him blood impulses for count time not utilizing acceleration etc,i've...

Homework Statement For example particle performs a motion in x-y plane. In y there are walls from both side so particle can go in y direction from zero to h. I need to plot trajectory. If I got trajectory y=x^4-x^2 then \lim_{x\to \infty}y(x)=\infty[/B]Homework EquationsThe Attempt at a...

I had a discussion with someone who studies psychology recently and she was referring to mental stress as of what I thought being called physical stress. Namely while she was talking about mental stress she mentioned stressors and hormones. So my problem: Stress = tension Physical =...

How Can I Prove this Physically Homework Statement [/B] So I need to do a project where I prove centripetal acceleration. All the cases I've seen of where it's proved is using formulas, though I need an actual project. By an actual project I mean something like...

My question is how we describe a harmonic oscillate. Wikipedia says, "a harmonic oscillator is a system that, when displaced from its equilibrium position, experiences a restoring force, F, proportional to the displacement, x." My question is, how is the harmonic oscillator a "system"? I thought...

I am working on a PDE problem like this: Consider the wave equation with homogeneous Neumann-Dirichlet boundary conditions: ##\begin{align} u_{tt} &= c^2U_{xx}, &&0<x<\mathscr l, t > 0\\ u_x(0, t) &=u(\mathscr l, t) = 0, &&t > 0\\ u(x, 0) &=f(x), &&0<x< \mathscr l\\ u_t(x, 0) &=g(x), &&0<x<...

I've recently read in this article http://www.en.uni-muenchen.de/news/newsarchiv/2013/f-m-77-13.html that "In the world of classical mechanics, the state of a physical system and its future evolution is fully determined by the instantaneous locations and velocities of its constituent particles"...

I'm a QM noob/newb trying to understand the physical implication of a wave packet, in my mind it is something like this: On the x-axis there is displacement (vibration), probability on the y. I Imagine stretching and compressing the wave packet. When I stretch it out, the amplitude must...

Hi everyone , i was wondering for a while to get a satisfactory proof of the equation : e^i*pi = -1 yes , i know it can be derived from euler's formula ... which is e^i*x = cosx + isinx ( which can be proved using differential calculus ) so, e^i*pi = cos(pi) + isin(pi) ( which leads to the...

It seems to me, at least when it comes to quantum mechanics, "information" has become the most basic unit. Like, quantum entanglement works to the point that information is extracted, and one can even revert certain things by making sure the information is destroyed. Same with the discussion...

Homework Statement I am given the following coupled differential equations: \begin{align} (r^2+1)\ddot{θ}+2r\dot{r}\dot{θ} &= u1\\ \ddot{r}-r\dot{θ}^2&=u2 \end{align} together with the following expression for the kinetic energy: \begin{align} T &= 0.5(r^2+1)\dot{θ}^2+0.5\dot{r}^2...

We can mathematically derive the equation of wave, \frac{\partial^2 y}{\partial t^2} = v^2 \frac{\partial^2 y}{\partial x^2}, where v is the velocity of wave propagation. Can we prove this equation physically (not just taking derivatives of the equation of wave, but making physical meaning in...

This is a repost because i realized i put it on the wrong forum section. After getting Kleppner and Kolenkow's second edition textbook I began my exploration of physics. I'm a sophomore in high school and VERY ignorant in regards to physics so if this question make no sense set me straight. I...

How can we sure that physical laws are always the same in all the universe?

Hi! I have a simple question regarding the realization of systems. In my university course books, it's mentioned multiple times that a system with a transfer function G(s) is realizable, if the denominator's degree is at least that of the numerator's degree. I found the same statement on the...

Are physical waves, like sound waves, or water waves, real physical objects like matter?

I majored in neuroscience and applied math in college and want to do computational neuroscience research long term. Being at the crossroads of biology and physical sciences, I think a lot about how the two "worlds" view each other. The lab I'm currently in has some people directly from the...

What i basically mean by this is that at this point in time we have classical and quantum physics, both need a different set of rules to describe their phenomenon due to the size of their appropriate systems why is this and does that mean we could also say the same for immensely large systems...

Is the wave function ( ex. electron wave function) just a mathmatical equation or a real physical object? I know that it's widely known that it's just an equation however some researchers say that they have proof that it's real. Here is the link...

I'd like to know the physical mechanism of oleum "fuming" on its surface. Dissolved SO3 reacts very exothermically with some air humidity. Why does the mist occur instead of dissolving created H2SO4 in the solution?

Hello everyone, I'd like to know if my understanding of local and integral quantities is clear. An integral quantity refers to the entire physical system, it is not defined point by point. A local one is defined point by point, for example ρ(x,y,z). Can I consider the charge dq as a local...

I cannot picture the physical meaning of the maximum proper distance at time of emisson. In the benchmark comological model the plot of (H/c) * (Proper distance at time of emission) versus z (the redshift) shows a maximum at z=1.6 for a proper distance of emission = 1800 Mpc (mega parsecs). I...

17:47 - dlbeeson: Is there any benefit of setting capacitance of an LC tank to resonate an inductor at its natural physical resonance frequency, like a tuning fork frequency? Like a brass pipe hanging on a string in a wind chime, the inductor must also have some physical resonating frequency...