# What is Rotating disk: Definition and 87 Discussions

The Rotating disk viscometer, or "Mooney Machine" as it is sometimes referred to in the rubber industry, is the standard viscometer for measuring material viscosity and scorch time for rubber before vulcanization. It was developed in the 1930s by Melvin Mooney. For a specific temperature, scorch time describes how long it will take the material to vulcanize. For example, a scorch time at ambient temperature indicates the rubber will be able to remain unvulcanized at room temperature for an extended period of time.

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1. ### A Forces on rotating disk object

Forces on rotating disk object Hi. Is it convenient to ask following question. Suppose we have solid circular object and 5 different moments like in the picture:In moment 1 we apply force (downwars direction) so as to start rotating the object around center of the mass (green dot) , Only...
2. ### Circular Motion: A coin on a rotating disk

I believe I've solved this problem, however, I got through it pretty quickly and since it's the last problem on the assignment, I feel that I may have had an oversight. For part a, I got: fs=md(α^2)(t^2) and for part b, I got: ω=Sqrt((µs*g)/d) Could someone confirm my answers? I've attached a...
3. ### B Time Dilation on Rotating Disk: Clocks on Disk Perspective

Obviously, a third observer who is at rest with respect to the disk will see that the clock on the outside has a much faster velocity than a clock on the interior of the disk, so clearly the outside clock will show that it has measured less time. But that's one question. What about looking at...
4. ### A Mass dropped onto rotating disk

Picture a flat disk of radius r with a radial vane. The disk is rotating at angular velocity w. Assume the vane is straight, starts at the center and ends at the perimeter of the disk. A very small round mass ( of m grams) is dropped onto the disk very near the center. The vane contacts it and...
5. ### I Clock synchronization for ring-riding observers on rotating disk

Hello, reading the wiki entry for Langevin observers on rotating disk - Born_coordinates I'm struggling with the following quoted sentence: But as we see from Fig. 1, ideal clocks carried by these ring-riding observers cannot be synchronized. I do not grasp why, starting from the figure...
6. ### Masses Moving Radially on a Rotating Disk

m = 60kg, ω0 = 2.094 rad/s, I of disk = 130 kgm^2 , outer position ro = 1.5m, inner position ri = 0.3m ∴Fifth object : Ffriction = m.ac μ.m.g = m. v^2 / R => vmax = √ 3. (1.5m) . (9.81 m/s^2 ) = 6.64 m/s => ωmax = 4.43 rad/s so when the fifth object move with greater speed than vmax...
7. ### Dipole moment of a rotating disk

I could do the first part of the question with ease but second part I am not sure how to proceed. Should we calculate the magnetic field at d(where the loop is) and infer something from that for it's motion?? Plz help me out Thanks in advance
8. ### Magnetic field of a rotating disk with a non-uniform volume charge

-------------------------------------------------------------------------------------------------------------------------------------------------- This was a problem introduced during my classical electrodynamics course. I am not 100% sure, but I think I've solved up to problems (a) and (b) as...
9. ### I A cold, massive, rotating disk galaxy 1.5 billion years after the BB

Neeleman, M., Prochaska, J.X., Kanekar, N. et al. A cold, massive, rotating disk galaxy 1.5 billion years after the Big Bang. Nature 581, 269–272 (2020). https://doi.org/10.1038/s41586-020-2276-y Abstract Massive disk galaxies like the Milky Way are expected to form at late times in traditional...
10. ### Releasing a hollow cylinder on a rotating disk

There is no net external torque since the cylinder is slipping (no friction), so the angular momentum should be conserved. $$L_f=\frac 12MR^2\omega_i=\frac 12\times3.8\times0.52^2\times50\times\frac{2\pi\times0.52}{60}$$
11. ### Rotating Disk and Hanging Mass Calcululations

I used the above equations to solve for tension, torque, inertia, and angular acceleration. Are the formulas I used correct for the given system? How can I calculate Inertia from the trendline equation, I'm drawing a blank.
12. ### Conservation of Energy and Angular Momentum in a Rotating Train-Disk System

Homework Statement [/B] A train stands in the middle of a rotating disk with an initial angular velocity of $\omega_i$. The mass of the train is m and the moment of inertia of the train-disk is I. At one point the train departs on a straight track to a distance R from the disk's centre. (R...
13. ### Determining the Speed of a Rotating Disk with a Constant Force

Homework Statement A solid uniform disk of mass 21.0 kg and radius 85.0 cm is at rest flat on a frictionless surface A string is wrapped around the rim of the disk and a constant force of 35.0 N is applied to the string. The string does not slip on the rim. 1- When the disk has moved a...
14. ### Rotating disk and its dynamical parameters

Hey all, I have a question that I am trying to figure out. It is more qualitative than anything, but I am concerned with the concepts that are involved in a scenario like this. Suppose we have a rotating disk with the plane of the disk perpendicular to the z-axis. Now we send a particle upward...
15. ### Braking Force from Eddy Currents on a Rotating Disk

Hello! I'm currently working on a project that will utilize the phenomena of eddy currents to apply a braking force to a rotating disk. Some background on this project: My team was tasked to create a physical therapy training device to train patients in wheelchair propulsion at resistances lower...
16. M

17. ### Pendulum on the end of a rotating disk

Homework Statement There's a pendulum with mass m and longitude L strapped to a disk with radius R that rotates with an angular velocity ω. Calculate the angle that the pendulum is shifted (Φ) depending on ω. You are given m, L, R, ω, g. Calculate Φ depending on ω. Little drawing (with my...
18. B

### Ball in Rotating Disk: Kinetic Energy, Work, and Power

Homework Statement A disk of radius ##R## has a cylindrical hollow that goes through it crossing its center ##O##. The disk rotates around its central axis with constant angular speed ##\vec{\omega}##. A little ball of mass ##m## and with the same radius of the hollow, is at a distance ##R_0##...
19. ### Moment of Inertia of a Rotating Disk

Homework Statement Given a non magnetic rectangular plate with dimensions: L & B. The plate is of uniform density and thickness.There are 2 points equidistant from the center of the rectangular plate along the line at B/2. Both of these pivot points have 2 disks of radius R and mass M that are...
20. A

### Finding tangential acceleration of a rotating disk

Homework Statement Attached. Homework Equations Tangenital acceleration=r*alpha 3. The Attempt at a Solution I thought it was just simply r*alpha=2*20=40 (choice A), but the answer key says choice B. I'm not really sure where I could have went wrong or its possible that there is a mistake...
21. ### I Clocks ON a rotating disk: What happens?

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)...
22. ### B Rotating Disks: Particle Movement & Spin

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)...
23. ### I Time dilation of a rotating disk

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...
24. ### Find the temperature increase of a rotating disk

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...
25. ### Rotating disk find the radial and transverse velocity

Homework Statement Homework Equations rXF ?? The Attempt at a Solution T= 6 N (r =1) T = 12 N (r=2)
26. ### Trajectory of pendulum in frame of rotating disk under it

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...
27. ### Two Rotating Disks Contacting Along Edge

Homework Statement Two disks, rotating in the opposite direction of the other, are held together on their rotating ends, acting as toothless gears. The bottom disk is slightly skewed in one direction, and therefore causes a frictional force on the top disk, and thus an equal and opposite force...
28. ### Rubber on a rotating disk (angular velocity, forces)

Homework Statement We place a rubber on the edge of a rotating disk. What forces act on the rubber? At what angular velocity, why and in what direction will the rubber fly off the disk? Homework Equations http://images.tutorvista.com/cms/formulaimages/83/angular-speed-formula111.PNG The...
29. ### Gyroscope on rotating disk

Homework Statement Describe the motion of a gyroscope with center of mass fixed on a rotating disk in coordinates of an observer which is at rest on the disk in the absence of gravity. Homework Equations The hint given was to somehow use Fermi transport, so I'm guessing: \mathbb F_u X=\nabla_u...
30. ### Rotating Disk in Magnetic Field

Hi I am having a difficulty understanding how to write the circuit equation inside a disk which rotates in magnetic field. the disk is made of conductor material. the resistance of the disk is: r the answer is: ir=emf+v(a)-v(b) if someone could explain it would be great! and how do i know where...
31. ### Rotating Disk and two students?

Homework Statement Homework Equations Read below The Attempt at a Solution A) D. As the mass of the students gets further away from the axis of rotation, the rate slows down (remember the skater with arms out). B) T. No explanation currently... C) ? D) T. The students exert a force on...
32. ### Relative Motion Analysis: Acceleration of rotating disk

Homework Statement A slotted link AC is is driven by the peg P connected to a rotating disk. Point A is fixed. Determine the link's angular velocity, \omega_{ac} and acceleration, \alpha_{ac} when the angular velocity and acceleration are \omega and \alpha , respectively. \omega = 6...
33. ### Help with torque calculation of underwater rotating disk?

Hello Guys, I have a disk of diameter of 150mm and thickness of 10mm which is rotating at the constant speed of 100rpm. The disk is inside water which is approximately 4-5 cm below the surface. Disk is horizontal (parallel to the water surface). Disk is attached with the shaft of the motor. At...
34. ### Viscous damping acting on rotating disk

I am looking for a way to calculate the torque, hence the viscous damping coefficient per T = c*w, acting on a rotating metal disk in an oil sump. How can I go about it? Thanks! PS. I am not a ME so please forgive my ignorance.
35. ### Rotating Disk and Time Dilation

My question is about comparing the time dilation of a clock on a spinning disk versus a clock in the vicinity of a massive object. It seems there should be a connection between the two, because of the equivalence principle, but I'm missing something because I don't quite get the answer I would...
36. ### Calculating Torque & Power of a Rotating Disk

Homework Statement So I am calculating torque and power for a disk of radius 0.5 m that is subjected to a force of 50 N at its periphery and is rotating at angular velocity of 100 rad/s. Find torque and power.[/B]Homework Equations Torque= radius x Force = 0.5m *50N = 25Nm Power= dW/dt=...
37. ### Calculating Torque for Rotating Disk: Specs, Friction, and Weight Considerations

Hi all, I am trying to calculate the torque required by the motor to rotate a disk at a constant speed. Specs are as follows: 1. Disk radius =80mm 2. Disk Thickness =2 mm 3. Disk Weight =50gm 4. Constant speed= 3000rpm(CONSTANT) 5. Motor friction torque= 1mNm 6. Disk position parallel...
38. ### What Is the Minimum Velocity for a Sphere to Traverse a Grooved Disk?

Homework Statement We have a disk of mass M and radius R placed on a horizontal plane. A cylindrical groove of radius r is made on a diameter.Now a sphere of mass m and radius r is placed in the groove at the circumference of the disk. At t=0 the whole system is rotated with an angular...
39. ### Find radial imprint on rotating disk

This problem came up after drawing a line on the spinning rotor of a food processor. I was idly musing about relativity (parallel motion and perpendicular motion). Maybe some ancient mathematician found the solution while working clay on their potting wheel! Here it is: A flat disk rotates...
40. ### A Spider on a rotating disk conservation of momentum

Homework Statement A 45 rpm record in the shape of a solid disk 25 cm in diameter and mass 0.1 kg rotates about a vertical axle through its center. A 15 g spider rides along the edge of the record. Calculate the final angular speed of the record if the spider drops off without exerting a...
41. ### Kinematics problem -- Cat chasing a mouse on a rotating disk

Homework Statement A mouse starts running on a circular path of Radius = 28m with constant speed u = 4m/s. A cat starts from the center of the path to catch the mouse. The cat always remains on the radius connecting the center of the circle and the mouse and it maintains magnitude of its...
42. ### Expansion tensor on rotating disk

Hi Everyone, Suppose that we have cylindrical coordinates on flat spacetime (in units where c=1): ##ds^2 = -dt^2 + dr^2 + r^2 d\theta^2 + dz^2## I would like to explicitly calculate the expansion tensor for a disk of constant radius R<1 and non-constant angular velocity ##\omega(t)<1##. I...
43. ### How much sand is needed to slow the rotation of a disk?

Homework Statement a disk of radius 40 cm is rotating about an axis through its centre. the moment the inertia of the disk is 0.015 kg m^2 and it is turning at 3 rev/s. sand falls on the disk at a distance of 20 cm from the axis and builds a 20 cm radius sand ring on the disc. How much sand...
44. ### Rotation: Speed of an object as it slips off a rotating disk

Homework Statement A 75g mass sits 75cm from the center of a rotating platform undergoing a uniform angular acceleration of 0.125rad/s . The coefficient of static friction between the mass and the platform is 0.250. What is the speed of the mass when is slides off? A. 0.889 m/s B. 1.26...
45. ### The rotating disk of Albert Einstein

Hello To demonstrate that we can deduce from special relativity the existence of an observer who finds that his three-dimensional space is not euclidean (a conclusion that is false in my opinion), in subsection "Behaviour of Clocks and Measuring Rods on a Rotating Body of Reference" of his...
46. ### Interval ds^2 on Rotating Disk - Explained

What is ds^2 on a rotating disk?
47. ### Rotating Disk Spinoff: Is 3D Timelike Congruence Born Rigid?

Let me apologize in advance for not reading the entire rotating disk thread. I think that the following question is closely related, but if it was answered in that thread, I didn't spot it. Let us consider the following timelike congruences, which maps congruence parameters t,r,theta and z...
48. ### Faraday's law on rotating disk

Homework Statement A metal disk is rotating with constant angular velocity in a constant magnetic field perpendicular to it. Use Faraday's law to fint the the induced voltage difference between the two points on the wire. The attempt at a solution So to use Faraday's Law, I need to...
49. ### Rotating disk/ sphere and moving mass along it

Coriolis effect - In a non-friction system, f I roll something along the surface of the planet from on of the poles to the equator, it will appear to move to the west, it will essentially stay behind the planets rotation and actually rotate it in the opposite direction. Now, if we add friction...
50. ### Rotating disk dropped onto another rotating disk

Homework Statement A wheel, mounted on a vertical shaft of negligible rotational inertia, is rotating at 500 rpm (CCW from above). Part a) asks to find the new angular velocity if an identical wheel is dropped onto the shaft. I got this part right. Part b) is: Now suppose the dropped wheel...