2d Definition and 1000 Threads

Hi, I have problems with the following: Number of modes for a 2d crystal with one atom per primittive unit cell. 1. Number of discrete vibrational modes? Should there be 2N of them? That is what I come up with if I think of one transverse and one longitudinal mode for each k. But I am...

I am looking at an object that diffuses randomly inside a circular plane. What is the easiest way to find the expectation value for how long would it take on average to reach the wall if it was initially placed at a random position? If it is easier: what if the initial position were the...

Vector, by definition, have 2 or 3 scalar components (generally), but the curl of a vector field f(x,y) in 2D have only one scalar component: \left ( \frac{\partial f_y}{\partial x} -\frac{\partial f_x}{\partial y} \right )dxdy So, the Curl of a vector field in 2D is a vector or a scalar?

Football Player 1 (mass m1 = 72 kg) has just caught a pass at the 50 yard line when he is tackled by Football Player 2 (of mass m2). Each player was initially moving at an angle of theta with respect to the 50 yard line at 8.0m/s. the tackle is a perfectly inelastic collision and the players...

Well when I watch movies I see space time as 2d. But how do we see the space time from Earth to a region lower than earth.

A simple question about elasticity theory/finite element method: Suppose I have a tetragonal 2D piece of a linear isotropic elastic material, that has Young's modulus ##E## and Poisson's ratio ##\nu##. The vertices of the tetragon are at positions ##\textbf{x}_{1}##, ##\textbf{x}_{2}##...

Please excuse me for my less knowledge. I always tried to physically visualise mathematics facts. My first question is " Is 1D space of physics a subspace of 2D space of physics and so on... So in this way our 3D space is a subspace of 4 D space(spacetime). Can I imagine applying all properties...

I was trying to deduce the 2D Rotation Matrix and I got frustrated. So, I found this article: Ampliación del Sólido Rígido/ (in Spanish). I don't understand the second line. How does he separate the matrix in two different parts? Thanks for your time.

Projectile Motion 2D -- Spring Launched There is this ball launched from a slingshot. Given the mass is 0.9 kg at the angle 60° to the horizontal, with k=750 N/m and is stretched by length l = 0.6 m. The ball is shot 1 m above the ground. (g=10 m/s2). The questions are to derive the equation...

Homework Statement Mortar crew is near the top of a steep hill. They have a mortar. They angle this mortar at an angle of \theta = 65° . The crew fires a shell at a muzzle velocity of 228 ft/sec (69.5 m/s). How far down the hill does the shell strike if the hill subtends an angle of \phi =...

Hello Guys, This is my first post here. I need help on my homework that I have been working on all evening. Basically I am given video data. 10 trials of a plastic ball in projectile motion. I have to use Logger Pro. Four things I need to find out for each trial: x-velocity y-velocity...

1. Homework Statement Two particles of mass m are connected by a light inextensible string of length l. One of the particles moves on a smooth horizontal table in which there is a small hole. The string passes through the hole so that the second particle hangs vertically below the hole...

2D Kinematics -- 2 rocks off a bridge Homework Statement Heather and Jerry are standing on a bridge 60m above a river. Heather throws a rock straight down with a speed of 14m/s . Jerry, at exactly the same instant of time, throws a rock straight up with the same speed. Ignore air...

Homework Statement A basketball, thrown off a cliff with a velocity of (30.0, 25.0) m/s, lands on the ground 8.00 s later. In the absence of air resistance, what is the distance the projectile lands from the base of the cliff?Homework Equations...

These are the papers it's based off of.. http://mredwards.net/Files/Problem%20D%20Horizontal%20Projectiles.pdf http://www.mredwards.net/Files/Problem%20E%20Projectiles%20from%20an%20angle.pdf My class uses g for gravity and delta x, vx etc...

Hello i wasn't sure if to ask this in here or in homework! I stumbled upon an assignment to build the model of photon gas in 2D space. in the answer it was stated that the light have 2 polarization states in 2D model, how come? the field have only one way to propagate regarding the wave...

Homework Statement http://postimg.org/image/bh4tzmd4l/ Can someone explain to me what "acceleration of the truck relative to the crate means"? What should I do first in trying to solve this?

Homework Statement In the diagram attached a bar weighs 500 kg and is a 2D plane rigid body with mass centre at G. At the instant shown, the bar is moving horizontally at but reducing speed, causing horizontal deceleration as shown by vector a=-7i m/s2. At the same time, the bar is being...

Homework Statement A 1.0-kg particle is moving in the +x direction at 4.0m/s when it collides elastically with a 4.0-kg particle moving in the −x direction at 1.0m/s After colliding the 1-kg particle moves off at 130 counterclockwise from the positive x-axis. Find the final speeds of both...

Does a photon, or any particle that travels at c, believe the universe to be 2 dimensional?

Hello Everyone, Happy Thanksgiving. I have physics issues. I went around the entire boundless universe in the last two days, and found out the Schrodinger forgot to develop the math for the momentum expectation value for a 2-D particle in a box. It's nowhere to be found. I am a chemistry major...

Is there anyone out there that knows how to define the p operator for a 2-d box. Please can you give a full answer, and not only a hint. I think that no one on this planet knows what it is. I have looked all over the internet. If there is no answer. Why don't people just say it? I think nobody...

Homework Statement A small block of mass m is sliding around the inside of an L-shaped track of radius r. The bottom of the track is frictionless; the coefficient of kinetic friction and the wall of the track is μk. The block's speed is v0 at t0=0. Find an expression for the block's speed at...

Hi all. I have a grid with 4 points, A, B, C, and D. Each valid move is either going to the right for one block or going down for 1 block. Here is the grid. I need to calculate the following: a) How many different valid routes from A to D? b) How many valid routes from A to D that must avoid...

Hey guys, I'm new to this forum and was hoping to get a clear answer regarding the difference between 1D, 2D and 3D flows in hydraulics (ex. 2D Numerical Model...) ? Thanks a bunch! -A.

Hello, Does anybody know/had experience with software that can turn 2D images to 3D models in CAD program, preferably in an offline environment (not on cloud)? The resulting model has to be accurate enough for aerospace engineering purposes. from looking online, I really didn't find...

Homework Statement A 42.5kg person is going down a hill sloped at 42.0 degrees. The coefficient of kinetic friction between the snow and skis is 0.180. How fast is the skier going 4.56 seconds after starting from rest? Homework Equations Is ffkmax equal to net force? The Attempt...

Homework Statement An object is hanging from three ropes. The first rope is vertical and has a tension of 16N. The second rope leads to the right and makes an angle of 70 degrees with the ceiling and also has a tension of 16N. The third rope leads to the left and makes an angle of 40 degrees...

Hi, I want to find out how thick/big/fat is the object in the image. For example, there is a tree in the image(photograph), I want to use MATLAB to calculate how big the tree trunk is. Problem: Find out the perimeter of trunk as shown in the first picture (named "perimeter.PNG". attached...

Homework Statement Si(001) has the following lattice vectors in a (2x1) reconstruction \vec{a'_1} = \vec{a_1} + \vec{a_2} \vec{a'_2} = -0.5 \vec{a_1} + 0.5 \vec{a_2} Calculate the reciprocal lattice vectors of the reconstructed unit cell, \vec{b'_1} and \vec{b'_2} in terms of...

So consider a 2D system with a circular potential and a spin-orbit interaction: V(r) = V_0 \theta(r_0 - r) + c r_0 V_0 L_z S_z \delta(r-r_0) where θ is step function. So the operators Lz and Sz commute with the Hamiltonian are are therefore conserved quantities. For the same reasons...

Homework Statement Consider a molecule with an electric dipole moment d. The Hamiltonian of a molecule in the external electric field E is: \hat{H} = \frac{\hat{L^2}}{2I} - dE \cos{\theta}, where the polar angle \theta characterises the orientation of the molecule. (We have chosen the field...

Homework Statement Let a and b denote two 2D vectors a = <a1, a2> b=<b1, b2> show directly that a . b ≤ ||a||||b|| Homework Equations The Attempt at a Solution Im looking for a place to start here. Should i start by computing the dot product of a and b and then also finding the magnitude of...

Homework Statement A stone is thrown horizontally from a height h above the ground (h > 0). The stone hits the ground after having traveled a horizontal distance x (x > 0). What is the expression for the initial speed v of the stone? Neglect air resistance. (please use the variables x and h...

1. Problem The kicker stands 50 m from the goalpost that is 3 m high. She kicks with an initial velocity of 24.5 m/s. She just makes the goal height-wise, but did the ball travel far enough? She kicked at an angle of 35.28 degrees. 2. Homework Equations S = (1/2)at^2 + V0t + S0 S =V0xt...

Homework Statement A block of ice starts from rest on an apartment building’s roof, which slopes at 41° below the horizontal. The block slides down the icy frictionless roof for 5.0 m and then leaves the edge, which is 12 m above the ground. a. How far from the building does the block strike...

Homework Statement http://imageshack.us/a/img812/8836/5tfn.jpg Uploaded with ImageShack.us Find F such that the moment around A will not exceed 1000N*m for any value of θ. Homework Equations M = fdThe Attempt at a Solution I got the right answer, I found the distance of a -> b AB= √( (2^2)...

Im sorry I just realized this is in the wrong subforum... Homework Statement Hello Everyone! I am new here and am having trouble with this webassign question. I was able to work out the answer to the first two but the last two are giving me trouble. I am not sure if this is right subforum to...

Hi! I am trying to compute the natural frequency of a system and I also need to add the added mass term to my equation. The object I have is a torus and is basically in heaving motion. I found a good paper, which gives a formula for 3d added mass and 2d added mass. I would figure that I...

Considering d=2 or d=3, the Ising model exhibits a second order phase transition at the critical temperature T_c, where the system goes from an ordered phase (spins preferably aligned in a certain direction) to a disordered one. This is reflected by the behaviour of the susceptibility, similar...

Hello, I hope this is the right section to post this question. While analysing the asymptotic value of a ratio of a bessel and a hankel function, I reduced it to something of the form [(1 + β/n)^ n * (1 + n/β)^ β] / 2^(n+β) ; n and β are integers and greater than 1 how do I show that...

Hi all, I would like to know if there exists any method to represent multidimensional vectors on a 2D plot so using extracting any unique features of those vectors. Can eigen values be used for such purposes like dimensional reduction. If so how ? I would like to know more about these...

I am a little confused about the Mermin-Wagner theorem, and the assumptions it makes, and I would like to better understand the 'exceptions' to the rule that occur in practical (non-ideal) scenarios. As is my understanding, The Mermin-Wagner theorem states that there cannot be spontaneous...

I think no matter what are the mass of two objects, there must be a fix angle between the angle of two direction. Is that using the center mass reference to calculate? I say that because we can prove that when the two objects with same mass collide, then the angle between the direction of the...

while it has been extensively proven that any 2D map can be colored with at most 4 colors, has any hypothesized why that is (outside the computer programmed brute force method)?

Hi. Me and my dad (math teacher) are having some trouble finding the answer to a seemingly fairly easy problem. It is somewhat similar to projectile trajectory math but with the difference that the projectile have an initial velocity and there's no gravity, only acceleration. Imagine the...

Homework Statement A ball rolling with an initial velocity of 40m/s[W] undergoes an acceleration of 5.0m/s2[N] for a period of 6.0 seconds. What is the displacement of the ball in the 6.0 seconds? The Attempt at a Solution Apparently the answer is 260m[W21°N] Please help!

Hi which 2D animation software would be good for adding simple animations in science class and for youtube presentations?. Eksamples would be: how galvanic cells work, simple biology drawings of cells, DNA etc. I’d like a program that’s quite straight forward but also gives me a lot of...

Hi, as I read in one of Hawking books, he predicted that a 2D life-form with an alimentary canal can not exist because it would fall apart. I was wondering about that, because I thought of an easy solution for this: with two movable chainings its still possible. I have made a graphic and...

Hi everyone, Is there a general method for finding out the moment of inertia of an irregular convex 2D polygon given the coordinates of its vertices? I have thought of one possible method: Split the polygon into multiple triangles and find the moment of inertia of each triangle around the...