Disk Definition and 819 Threads

Hello. The following situation I thought out confuses me so I am wondering where my mistake lies. A uniform disk of mass M and radius R sits on its edge. A string is attached to the highest point and pulled with a Force F in the x direction. The moment of inertia of the disk is MR^2/2 making...

The unit closed disk minus the point ##(0,0)## ##\mathbb{D}^1 \setminus (0,0): \bigg[(x,y) \in \mathbb{R}^2 | 0 < x^2 + y^2 \leq 1 \bigg]## is homeomorphic to the unit circle ##\mathbb{S}^1: \bigg[(x,y) \in \mathbb{R}^2 | x^2 + y^2 = 1 \bigg]## Since ##\mathbb{D}^1 = \big(\mathbb{D}^1 \setminus...

Okay, I will give a quick run down of what I am trying to do here. What I want to do is build a tesla turbine from old hard drive disks. Being that they're already rated for high RPM, it seems like a viable option. Now these disks are probably going to be aluminum and I am probably going to buy...

hi I'm an astronomy student and i was studying the standard accretion disk model and I've got some questions related to it.! why do we consider the accretion disk to be stationary in standard accretion disk model? and what are the limitations of standard disk model? and i just read somewhere...

I was reading about the Ehrenfest Paradox and it got me thinking about something (that I think is) similar: Suppose we take a large, flat, and rigid disk, and we attach to various parts of it a number of clocks (some very close to the center of the disk, some along the edge, others in between)...

Let some point P on the y-axis and let the disk of radius "a" to lie on the z-x plane perpendicular to y axis. All charge elements in a thin ring shaped segement of the disk lie at same distance from P. If s denotes the radius of such a annular segment and ds is its width, then the area is...

Homework Statement [/B]Hello, I have derived the equation for the gravitational force for a disk to be 2Ggm/a^2(1-x/sqrt(a^2 - x^2) when an object is added on top of the system. My question is would the force still be somewhat similar if the disk now had a small hollow of radius c...

Homework Statement A uniform disk of mass M = 3 kg and radius r = .22 meters is mounted on a motor through its center. The motor accelerates the disk uniformly from rest by exerting a constant torque of 1 n * m What is the time required for the disk to reach an angular speed of 800 rpm...

Homework Statement A small disc, radius r and mass m = 7.9 g, rolls on its edge. The friction with the track is enough to prevent slipping. When released, it rolls down the track (sketch) and reaches a circular section with radius R = 5.1 cm, which is very much greater than r. The initial...

Homework Statement The figure shows an overhead view of a 2.50-kg plastic rod of length 1.20 m on a table. One end of the rod is attached to the table, and the rod is free to pivot about this point without friction. A disk of mass 39.0 g slides toward the opposite end of the rod with an initial...

<Mentor's note: Moved from a technical forum and thus no template.> A ring's kinetic energy is integral of 0.5v2 dm. Distance X is rΘ, and Θ is defined as distance traveled/radius, so X is r*distance traveled / r. Velocity V is X divided by time, so V is r*distance traveled / rt, and I define...

Hi, I'd like to build a homopolar generator. Since generating magnetic fields of uniform density of any useful size is very tricky to do with off the shelf permanent magnets (I've tried!) I had the idea to use DC solenoids instead. But with a rotating helical plate in place of the cylindrical...

[Mentor's note : No template as this thread was moved from the technical forums] Hi all! I am working on finding the Lagrangian for the situation stated in the title. This is actually a Wolfram Mathematica demonstration as well in which they give you the Lagrangian. I am working on re-deriving...

When we rotate a disk, can this process be fully explained by looking worldlines of the particles the rotating disk is composed of, hence their x,y,z,t position "as time passes", or do particles have some kind of "facing direction", hence also spin(not the quantum mechanical notion of spin)...

A 2.5 inch diameter disk plate has 6 plates , 512 bytes per sector , 256 sectors , 5268 tracks per surface. What is the capacity of the disk in terms of Giga bytes ? In the solution of my book ..written: 6 plates = 6x2-2 = 10 recording surfaces // I don't understand this part. Could you...

Homework Statement Homework EquationsThe Attempt at a Solution This is the problem in Goldstein's classical mechanics exercise 1.11 I wonder why the solution doesn't consider rotational kinetic energy (1/2 I w^2) So, L= T = 1/2mx^2 + 1/2 I w^2 .

In the diagram, I am focusing on the area in the green circle. So this is basically 2 Faraday disk with the magnets opposing and concealed in a copper cylinder. Now if we spin the cylinder a current is generated such as the current following the red arrows. My Confusion: As the current passes...

Iv'e been recently interested in time dilation, but the relative time difference between two observers confuses me (i.e. that a high speed observer, and a stationary observer will each perceive the other's clock to run slow.) I thought of the following experiment to help me understand, but I'm...

Homework Statement Thin uniform disk with radius r, mass m, and moment of inertia 0.5mr2 is suspended from a cable line where one end is attached to a set point via a spring, and the other end is also attached to a spring but is moving in an upwards direction. Solve for the equations of motion...

Homework Statement Find the electric field at a distance z above the center of a flat circular disk of radius R Homework EquationsThe Attempt at a Solution My attempt to solve this was take the line integral from the center of the circle to the edge. Then, knowing the circle is symmetrical...

Hi, I have a disk of diameter r, and the mass of the disk is 1kg. I'm going to rotate the disk at its center. my question is: 1. let's say I put a load of m kg on top of the disk, does the moment inertia of the system is as simple as (m + 1kg)r2/2? 2. does the shape of the load put on top of...

Homework Statement A washer made of nonconducting material lies in the x − y plane, with the center at the coordinate origin. The washer has an inner radius a and an outer radius b (so it looks like a disk of radius b with a concentric circular cut-out of radius a). The surface of the washer is...

Homework Statement May I ask you something about a task from the last years test at faculty of mathematics and physics, University of Ljubljana, Slovenia ... There is a disk at the end of a pole. We cause some F dt tangentally on the disk, which causes the change of momentum. I need to...

Homework Statement Two 2.4-cm-diameter disks face each other, 1.9 mm apart. They are charged to ± 12 nC . What is the electric field strength at the midpoint between the centers of the disks? Homework Equations The Attempt at a Solution Q=12*10^-9 A= Pi * r^2 = pi*(.012)^2 Q/A=...

Homework Statement There is a disk with mass 50 grams put on a slippy surface (no friction!). Its radius is 5 cm. Mass of the weight is 20 grams. At the beginning there is no motion. How far does the center of mass of the disk move in 10 seconds? (answer: 91 m) How many turns does the disk in...

I had a drive that every few minutes makes a buzzing sound. Here's what SMART is telling me. ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 1 Raw_Read_Error_Rate 0x000b 071 071 016 Pre-fail Always - 61213753 2...

If trying to find a branch of ##(z^2-1)^{1/2}##, it can be shown that one acceptable answer is: ## i e^{0.5 Log(1-z^2)}## But I just want to clarify, is not the following an acceptable answer, too: ## iz e^{0.5 Log (\frac{1}{z^2} -1)}## It appears the argument of Log in both cases is always...

There is a solenoid on top of a disk with charges attached to it. and there is a clockwise current through the solenoid. So by disconnecting the battery, the current will lower, and hence the flux of the magnetic field though the disk will lower, and according to faraday's law, there will be...

Homework Statement Let's have a disk of mass ##m## and radius ##a## and massless rope tangled in it. One end of rope is tied to the ceiling and the disk is falling freely down. System has one degree of freedom. As a coordinate we can choose angle ## \phi## which says an angle of rotation from...

Homework Statement It's a Blackbody radiation problem: A beam of wavelength λ, in the state of right circular polarization, leads to an absorbent disk.The mass of the disk is m, it's specific heat is C, and its moment of inertia is I .The disk is initially at rest, but after a lapse of time...

Homework Statement We are given a disk with negligible thickness, a radius of 1m, and a surface charge density of σ(x,y) = 1 + cos(π√x2+y2). The disk is centered at the origin of the xy plane. We are also given the location of a point charge in Cartesian coordinates, for example [0.5,0.5,2]. We...

Homework Statement String is wrapped around two identical disks of mass m and radius R. One disk is fixed to the ceiling but is free to rotate. The other is free to fall, unwinding the string as it falls. Find the acceleration of the falling disk by finding the lagrangian and lagrange's...

for a disck rolling on a horizontal plane the kinetic energy should be the kinetic energy of the CM of the disk with respect to the origin plus the kinetic energy due to the rotation of the disc about his CM so T= 1/2 (M V^2) +1/2(I ω^2) where M is the mass of the disk and V is the velocity of...

Homework Statement Homework Equations rXF ?? The Attempt at a Solution T= 6 N (r =1) T = 12 N (r=2)

Hello, My DVD drive won't accept disks, mechanically. I can't put any disc in. The problem is this: out of the central circle came three parts which make the radius of the central circle larger, so disc won't fit in. How can one solve this? I send a picture to explain the problem. The large...

Homework Statement A child is at a playground, and chooses to try the spinning disc (see figure). The radius of the disc is 2.00 m, and the coefficient of static friction between child-surface and disc-surface is μs = 0.350. In the following questions, you must provide algebraic equations as...

I am working on a linear algebra problem like this: > Consider the set of all points $(x,y) \in \mathbb R^2$ as defined by $x^2 + y^2 \leq 25$. Prove that $x^2 + y^2 \leq 25$ is convex. Here is what I have made out so far: (1) $x^2 + y^2 \leq 25$ is a disk with center at the origin of...

So I am trying to find the volume of a solid with this information given to me: 𝑥=0 𝑦=0 𝑦=−2𝑥+2 However, when I go to enter this information into a disk method calculator, I don't have enough information to enter into the calculator, such as the lower function and limits. My question is...

Let's say I have a disk magnet that is a centimeter thick and 1 meter in diameter. Now let's apply an external field confined to a cylinder of arbitrary position, angle, and length. Let's say it has a diameter of << 1 meter, so very, very narrow. Let's presume that the external field lines are...

I know that the accretion disk of a black hole gets hot enough for powerful emission of x-rays, but does that disk get hot enough for certain elements to fuse?

Homework Statement Let's have a disk and massless rope tangled in it. One end of rope is tied to the ceiling and the disk is falling freely down. System has one degree of freedom. As a coordinate we can choose angle ##\phi## which says an angle of rotation from the start position. Find from the...

Homework Statement A uniform disk of mass m and radius R lies in a vertical plane and is pivoted about a point a distance ℓcm from its center of mass in (Figure 1) . When given a small rotational displacement about the pivot, the disk undergoes simple harmonic motion. Determine the period of...

Homework Statement Consider the pendulum depicted in the adjacent figure: a mass m is attached to non stretching chord of length `. Directly below the pendulum is a circular disc rotating with constant angular velocity w. We attach to the disk a frame whose x-axis is in the plane of the...

Homework Statement A dart of inertia md is fired such that it strikes with speed vd, embedding its tip in the rim of a target that is a uniform disk of inertia mt and radius Rt. The target is initially rotating clockwise in the view shown in (Figure 1) , with rotational speed ω about an axis...

Homework Statement You connect a light string to a point on the edge of a uniform vertical disk with radius R and mass M. The disk is free to rotate without friction about a stationary horizontal axis through its center. Initially, the disk is at rest with the string connection at the highest...

Hi, I'm just starting to use oommf. I wish to see the evolution of the magnetization of a dot, which has uniaxial anisotropy. Command lines I use are #Geometry proc Disco {x y z} { global Diametro Ms set rx [expr {2*$x-1}] set ry [expr {2*$y-1}] if...

Homework Statement The moment of inertia of the disk-clay system about the central axis of the disk is I = 1.5 kg m2 Disk's mass = M The clay's mass = 0.12 kg Calculate the mass of the disk? Homework Equations I = m r^2 The Attempt at a Solution I thought that the moment of inertia may just...

Hi all. I'm trying to figure out how is the normal (direction) applied by two disks on a rod which connects the two disks, in order to build the second law of dynamics. See figure. Hope you could help Thanks

Homework Statement Calculate the electric field at point P (refer to visual): Homework Equations I follow everything - except how the limits of integration for the u-integral ( ) are arrived at? The Attempt at a Solution u=x2 is the smallest value u can have, and u=x2+R2 is the greatest...

Ive got the following disk I am attempting to find the torque required to turn it 1/4 turn in 1/4 second. Am I correct when I am considering I(D)=1/2mr^2 as its a disk, and I(d)=mr^2? and The final moment of inertia to be I(D)+I(d)? Here is the disk I am speaking of...