# What is Rotating disc: Definition and 44 Discussions

A rotating biological contactor or RBC is a biological fixed-film treatment process used in the treatment of wastewater following primary treatment. The primary treatment process involves removal of grit, sand and coarse suspended material through a screening process, followed by settling of suspended solids. The RBC process allows the wastewater to come in contact with a biological film in order to remove pollutants in the wastewater before discharge of the treated wastewater to the environment, usually a body of water (river, lake or ocean). A rotating biological contactor is a type of secondary (Biological) treatment process. It consists of a series of closely spaced, parallel discs mounted on a rotating shaft which is supported just above the surface of the waste water. Microorganisms grow on the surface of the discs where biological degradation of the wastewater pollutants takes place.

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1. ### Moment of Inertia of a Disc: Is it paradoxical?

In deriving the MOI of a ring about its center perpendicular to plane, our teacher said think of ring as made up of ##dm## units each at ##R## distance from the axis therefore the MOI becomes: $$I=R^2\int{dm}=MR^2$$ If disc is considered to be made up of rods of ##dx## thickness, in this manner...
2. ### B Relative rate of clock ticks on the radius of a rotating disc

Currently reading Einstein's booklet on SR and GR. At this point SR has been explained but GR hasn't been introduced yet. The setup is like this: ##A## is present in an inertial reference frame and looking down on a flat rotating disc. ##B## is sitting on the edge of that disc, ##C## is sitting...
3. ### Rigid Body Problem Involving a Tilted Rotating Disc

Using these equations, I find L=0.02Nms, I=0.02Kgm^2 and KE=10mJ However, i don't think that this is the right method here.
4. ### Acrylic (PMMA) rotating disc tensile strength calculation

Hey folks, I've been looking around but can't piece this together as there are more than one equation and variable to take into account. My situation - I have a pmma material disc on an axis , the center hole (axis hole) is 20mm wide so a radius of 10mm, while the outer edge is at a radius of...
5. ### Elastic collision of particle and rotating disc

Consider the system of the mass and uniform disc. Since no external forces act on the system, the angular momentum will be conserved. For elastic collision, the kinetic energy of the system stays constant.Measuring angular momentum from the hinge: ##\vec L_i = Rmv_0 \space\hat i + I \omega_0...
6. ### Angular momentum of a rotating disc

"A smooth horizontal disc rotates with a constant angular velocity ω about a stationary vertical axis passing through its centre, the point O. At a moment t=0 a disc is set in motion from that point with velocity v0. Find the angular momentum M(t) of the disc relative to the point O in the...
7. ### Write an expression w1 of the angle shown in the first picture

A bicycle wheel rolls at a constant speed along a circular path on a horizontal surface. The wheel has a constant angle of inclination to the vertical direction and the distance from its center of mass G to the fixed Z axis is R. Determine the relationship between the angular velocity w1 around...
8. ### Particle moving in a rotating disc

Well, I tried plugging the data in the formula. I know that ##\vec a_b = 0; \vec \omega=3 rad/s ; \vec r## can be calculated using trigonometry. Then I also know that ##v_{relx}= 10 cm/s##, ##a_{relx}=15 cm/s^2##, ##\vec {\dot{\omega}}=-10 rad/s^2##. But how do I get ##v_{rely}## and...
9. ### What is the angular velocity in the center of a rotating disc?

I have a disc. The center of the disc is its center of mass and the motion of the disc is purely rotational (no translation). What is the angular velocity in the center of the rotating disc?
10. ### Probability of hitting a rotating disc

There are two points of the smaller disck such that a line is tangent to the two discks and passes by that point. If the particle leaves of any point belongin to the arch that connects these two points, then it will hit the other disck. So I managed to calculate the value of this arch and divide...
11. ### Rotational Movement of a Disc

I am doing a project, but am struggling to find relationships of proportionality or formulae between my dependent variables (angular velocity, displacement, acceleration of the disc and kinetic energy of the system) and my independent variables (falling masses and then the number of winds) or...
12. ### Conservation of Angular Momentum on a rotating disc

I have a disc that is rotating due to air being blown at its outer radius. The incoming relative velocity of the air is high, therefore the effect of friction supersedes the effect of conservation of angular momentum. The tangential portion of this velocity decreases due to the friction as it...
13. ### Rotating disc in a rotating magnetic field

Homework Statement :A metallic disc of radius R is placed perpendicular to a magnetic field B.Both the magnetic field and the disc rotate with an angular velocity w about the axis of the disc.Find the induced EMF between the center and the circumference[/B]Homework Equations Motional Emf=Bvl...
14. ### How Do You Calculate the Velocity of a Point on a Rotating Disc?

Homework Statement Find the velocity v of a general point on a plate rotating at 800 rpm which is r meters from the center. This is literally a copy and paste job. Homework Equations period = T = 1 / f ; f = frequency The Attempt at a Solution This is what I did please tell me if it is...
15. ### Rotating disc of radius R spinning at constant angular velocity

Ok, so here's the deal. I'm working on something that I SHOULD know the equations for after 5 years of school and a degree in mechanical engineering, but then again I can't remember why I walked into a room most times. So if ya'll could give me some guidance and at least a starting point I...
16. ### Rotating Disc with central hole

Homework Statement Problem and worked Example[/B] Homework Equations In worked example 1. Problem The Attempt at a Solution It's the part where I'm subtracting one stress from the other stress. I put it in parenthesis on the worked example. I don't think my method here is right, I've tried...
17. ### Torque of charged rotating disc in uniform magnetic field

Hi, I'm having an issue with finding a starting point for the following problem. I've looked through my magnetism and electrodynamic notes but was unable to find a starting point. Could someone please help direct me on the correct path? Thank you. Homework Statement A thin circular disc of...
18. ### Sliding Rod and Rotating Disc Question

Homework Statement A uniform rod AB of length L and mass m1 is connected by a pin joint to the center of a uniform disc of radius R and mass m2. The system is placed in a vertical plane (as shown in Figure 2) and released from rest with θ=45°. (a) Draw the free-body diagrams for the rod and the...
19. ### Spring mass on a rotating disc

Homework Statement I uploaded a figure demonstrating the problem w and i are constants and disc is horizontal. Disc mass is neglected. Vibrating mass only moves along the direction of springs -only horizontally at this position- [PLAIN]http://[url=http://postimg.org/image/yxuleosq1/]...
20. ### Reason for body to slip away from centre of a rotating disc

Why does a body kept on a rotating disc tend to slip away from the centre?
21. ### Mass pulled on a rotating disc

Homework Statement A disc of radius R and mass M lays on a smooth table. a smooth channel is carved along the diameter and on both ends there are masses m. one of the masses is attached with a wire to a small, almost weightless motor that is in the center. the other mass remains fixed in place...
22. ### A chain falling off a rotating disc

Homework Statement A uniform chain of length L = πR and mass M is placed on the upper half of a uniform thin disc of radius R and mass M. The disc is placed vertically and can rotate freely about its center that is fixed in space. With a small disturbance the chain starts to fall. Find out the...
23. ### Friction on a particle on rough horizontal rotating disc

A particle is attached to an inextensible string. The other end of the string is attached to the centre of a rotating rough disc. The string is shorter than the radius of the disc so the particle remains on the disc and moves in uniform circular motion. I don't remember the quantities but the...
24. ### Torque of a rotating disc with string

Homework Statement A disc is on a desk, with a rotation point underneath. A string is wrapped around it, and the end of the string has a mass attached to it. The string end is put over a pulley, and when the mass is dropped it causes the disc to rotate. We are given mass of the disc (80g)...
25. ### Lagrangian of a rotating disc with mass attached

Homework Statement A uniform disk of mass 2M, radius R, is mounted on a frictionless horizontal pivot through its principal axis. The disk has an additional point-mass, M, fixed to a point on its circumference. (a) Give the Lagrangian for this system. (b) Find the frequency of small...
26. ### How Is Torque Generated by Friction on a Rotating Disc Calculated?

If I have a spinning circular disc of uniform density, how would I find the torque generated by friction, if the disc is lying flat against a table with coefficient of friction μ? τ=Fxr, but what is F, and what is r in this case?
27. ### Thin rotating disc under constant acceleration.

In a different thread the Herglotz Noether theorem was brought up and it was mentioned that this theory implies it is impossible for a cylinder rotating about its vertical axis to remain Born rigid in a gravitational field even at constant altitude. This is an extension of the claim that a Born...
28. ### Blocks on a rotating disc connected by a spring

To understand centripetal force due to friction better, I came up with this problem. I'm not entirely sure of my solution, though, so I'd be glad if someone else took it up too and suggested a way to work it out: Two identical blocks, each of mass m, connected by a spring of spring constant k...
29. ### Object flying off a rotating disc

Why does an object on a rotating disc fly off the disc as the speed of rotation is increased? To accelerate, the object must experience a net force in the direction of acceleration -- in this case, away from the disc, perpendicular to the object's velocity vector. But what is this force...
30. ### Force applied on a rotating disc

I understand that if we apply a force on the axis of rotation of a spinning disc, the torque is in a different direction, and the axis is moved in a direction perpendicular to the direction in which the force upon the axis was applied, determined by the right-hand rule. But what if the force...
31. ### Kinetic energy of a rotating disc

if KE=1/2mv^2 and you have a circular object rotating, with it's mass uniformly distributed through the object (ie each part of the disc weighs the same) then obviously certain parts of the disc will be moving faster than others. therefore closer to the middle of the disc, you have more KE...
32. ### Mouse falls on rotating disc, find the work it needs to go to the center of it

Homework Statement mass of the mouse = 0.05 kg disc's radius = 0.2m disc's angular speed = 33 rev / min assume that the angular speed ω doesn't change Homework Equations tangential speed = ω * r The Attempt at a Solution well, what i did was: drew the vectors, one was the...
33. ### Force Required to stop a Rotating Disc

Homework Statement Essentially, I am trying to determine the force that must be applied to a rotating disc to that stop that disc from rotating in a certain time period. The disc is rotating at 5800 rpm, the disc has a radius of 5 inches, and a thickness of 0.087 inches. The disk is made...
34. ### Too Complex for me - multiple torques on rotating disc

Hi all... my first time here... I hope someone can help. I'm toying with a home project (in the early conceptual stage), and the attached picture shows "in general terms" what I'm trying to figure out. The outer 'wheel' rotates about its central axis, driven at that axis by a small motor...
35. ### Can I desgn a rotating disc without using a centre shaft

Is it possbile to spin a disc that has a hole in the centre like normal DVDs but without using a rotating centre shaft that is passing through the hole? The spining disc has to be supported too by a structure. Is there any mechanism to recommend?
36. ### Do the students exert a net torque on the rotating disc?

Homework Statement A large plate is balanced at its center and two students of equal mass stand at its center. The plate is rotated on a frictionless pivot about an axis through its center and perpendicular to its face. The students then begin to walk out towards opposite edges. (Select T-True...
37. ### Direction of Magnetic Field for a Charged Rotating Disc

Homework Statement The question actually asks for the equation for the magnetic field for the rotating disc; but all I'm after is the direction of the magnetic field. Homework Equations None were given; but I've been using: \nabla \times \vec{E} = -\frac{\partial \vec{B}}{\partial t}...
38. ### How to determine the torque of a rotating disc?

how to determine the torque of a rotating disc in order to find the power of motor? there is a rotating disc, and a ball will pass through and launched by the rotating disc. the initial speed is 20m/s, and i could determine the rpm from here. the information i have now: the disc diameter...
39. ### Rotational motion of rotating disc

You stand on the edge of a large rotating disc. It rotates at a constant speed. You walk towards the centre of the disc. What do you experience? radius is decreasing, therefore inertia and linear velocity are decreasing. but angular acceleration will increase. i don't know if I'm right
40. ### Question about the rotating disc

Consider a disc in the framework of special relativity. It's initially at rest in an inertial frame, and then you get it rotating in a way that respects the symmetry of the circle (e.g. by turning a thin rod through its center). There's no way that the acceleration of the different parts of the...
41. ### Stress energy tensor for rotating disc

Hi, i need calculate the stress energy tensor for rotating 3D-disc in arbitrary rotation. where i can find some hint or perfomed calculations? thank you
42. ### Coin on rotating disc. What forces?

1. If two coins are placed on a rotating disc (constant speed), what forces act on the coins, at what direction and in what proportions? (The coins aren't sliding) Gravity is one, and the normal force is the one counteracting on that. But what forces could be expected in a horizontal...
43. ### Rotating Disc & Speed of Light ?

Rotating Disc & Speed of Light ?! If a point on a disc's outer edge is traveling close to the speed of light and things contract in the direction of the acceleration at those speeds (relative to a stationary observer) would that mean the disc's radius stays the same but the circumfrance...
44. ### Can a Tachometer Measure the Torque of a Rotating Disc?

Hello All! I have one machine. The disc (Horizontal place) is rotating and connecting to the shaft which is connecting to gear box and ac motor. I would like to k now the torque of rotating disc for some interval such as 10s, 20s, 30s, to take reading , but I do not have money to buy...