Spinning Definition and 581 Threads

Moons orbit planets. Planets orbit stars. Stars sometimes orbit other stars. Stars orbit galactic centres. How to we know galaxies aren't orbiting super super super massive black holes or something along those lines. And it continues. How do we know this chain is not infinite? Thanks bros Fin

Centrifugal Force -- continue spinning indefinately in space? I believe it is correct that if you spin up an object in space, like a space ship, it will continue spinning indefinately unless/until another force is applied to stop it from spinning. Then centrifugal force would push the objects...

Hi, As part of an experiment I am doing I have a small uniform circular disc that is submerged in 20ml of a liquid and is spinning at 2000rpm for 60 seconds. The disc is 1mm thick and 40mm in diameter. I am trying to see what effect the spinning disc has on the growth of cells that are in the...

If an "Object A" spins at nearly "c", and this object also is moving at any given posible speed. What happen with an "Object B" on the surface of "Object A" .I asume that there's a mechanism that "fix" this relation between angular and linear momentum to conserve the speed limit of light, but I...

I came up with this problem, and solved for it, but I do question its accuracy, and id like to know how I could make it a better model. (it is not a homework problem) So, a block, of dimensions a (rests on the z axis) by b (rests on the y axis) by c (rests on the x axis), is moving with a...

Hi, please could someone explain the notion that particles of 1/2 integer spin do not look the same when turned through 360 degrees. This notion seems to crop up when I read around QM but nobody seems to explain how this came about. So my question is this - what experiment shows/confirms that...

If two balls were close to each other in a pool of water and each had some angular momentum but one was spinning one way and the other was spinning the other way what would happen? same question for if they both were spinning the same way?

Homework Statement http://puu.sh/5Qrxt.jpg Homework Equations τ = dL/dt The Attempt at a Solution I understand the initial and final angular momentum vectors in the diagram, and the answer seems to make sense. But when I initially solved it my logic was that since the axle...

Homework Statement A solid conducting disk of radius a rotates about its symmetry axis with angular speed ω rads/s. If there is a uniform magnetic field \mathbf{B} perpendicular to the disk derive an expression for the potential difference induced between the centre of the disk and its rim...

Homework Statement A guy is spinning on a chair with his hands at rest on his lap. As he is spinning, a large mass drops into his hands/lap. Does the guy continue spinning at the same rate, a slower rate, or a faster rate? Homework Equations L = Iω = m(r^2)ω The Attempt at a...

Homework Statement A famous practical joke makes use of a suitcase, inside which is mounted a flywheel which is rapidly spinning about a horizontal axis. Describe what a porter experiences when he tries to turn the corner carrying the suitcase. If the flywheel has a mass of 5 kg, a radius of...

In chapter 5, magnetostatics, of Griffiths' Introduction to Electrodynamics (third edition), there's a problem in the back of the chapter that asks you to calculate the force of attraction between the northern and southern hemispheres of a spinning charged spherical shell. The problem in its...

Stuck in this question -- 2 spinning disks brought together... Two disks are spinning freely about axes that run through their respective centres. The larger disk (R1 = 1.42 m) has a moment of inertia of 1180 kg · m2 and an angular speed of 4.0 rad/s. The smaller disk (R2 = 0.60 m) has a...

A disc of radius r is spinning about its center in the horizontal plane with a constant angular speed w (omega). A bug walks along the radius of the spinning disc traveling from the center of the disc toward the edge. The bug maintains a constant speed v relative to the disc. (In other words...

Consider a charged wire with constant linear charge density λ. The wire has length 2πa and is attached to the edge of a disc with radius a. In the central region of the disc (a circular region of radius b<a) a constant magnetic field B is applied (perpendicular to the disc). The magnetic...

"Rewinding" a black hole - Can a spinning black hole become a star? I couldn't fit all the important prerequisites and context in the title, so I'll set up the thought experiment here. Some of these assumptions are also questions, and might be easily refuted, thus answering the main question...

Hello, I'm working on my first year engineering project. I'm an electrical engineering major but this is a general engineering course. I'd like to know how I could figure out how much weight I would need to put on the wheels of a cart that is going to push a 2kg object (for about 3 feet)...

As titled: I would be satisfied with a qualitative explanation(pure physical), but it would be nice if someone can also provide the mathematical model. thanks

Homework Statement Iron atoms (atomic mass 56) contain two free electron spins that can align with an external magnetic field. An iron wire 3 cm long and 1 mm in diameter is suspended vertically and is free to rotate about its axis. A strong magnetic field parallel to the wire's axis is...

Homework Statement Two engineers are working together in a competition to launch a pumpkin as high as possible using a launching device that must be kept within a certain height. Since the engineers have a height restriction, they want to accelerate the pumpkin to a large speed before...

Hey, Got into a discussion with my friends over this: If you spin in your chair clockwise, since the Earth spins counterclockwise, as you start spinning by conservation of momentum the Earth would also start speeding up. Then, frictional dissipative forces from the air would slow you down to a...

Hi everyone, I was wondering what forces would counteract the force of gravity on an object which is spinning horizontally on a string. I realize its a component of the tension, but how does the force come about? Is this force also the reason that the object's plane of rotation rises when we...

According to my understanding of the LCDM Friedmann–Lemaître–Robertson–Walker metric, the Universe under such a metric model is homogeneous and isotropic, and does not have any spin rotation. Friedmann–Lemaître–Robertson–Walker metric: c^{2} d\tau^{2} = -c^{2} dt^2 + a(t)^2...

Homework Statement Find the period of a pendulum consisting of a disk of mass M and radius R fixed to the end of the rod of length l and mass m. How does the period change if the disk is mounted to the rod by a friction less bearing so that it is perfectly free to spin? The centre of the...

Homework Statement If you swing a ball in a vertical circle using a thin string, at the bottom of the circle the tension in the string must be greater than the ball's weight. True or false? Homework Equations F = mvv/r F = mg The Attempt at a Solution The correct answer, it says...

Homework Statement Let us explore whether there is any way to distinguish acceleration due to rotation from acceleration due to a gravitational force. Imagine a deep bowl with a small volume of milk in it. (a) What happens to the milk when you spin the bowl about a perpendicular axis that...

For the basic principle of motors and electromagnetic induction, when a wire loop with a current running through it is put in a magnetic field, wouldn't it only spin until it reached a certain point (i.e. flat, 180 degrees) before it stopped? What accounts for this? Is it that the loop must...

Let's say you have a strong spherical neodymium magnet (for the purposes of this example, let's give it a 1 cm diameter), and you were to place it on a machine which rapidly rotates the magnet. If you were to rotate it at 100 MHz, could you build an FM radio transmitter? Supposing it were...

Imagine that we have a wheel spinning with the axis of rotation normal to the Earth's surface. For convenience, let's assume that the wheel is located somewhere in the north hemisphere. According to the definition of the Coriolis force, every little particle dm of the wheel has a coriolis...

Homework Statement An object of mass 2 kg is held in circular motion by a string of negligible mass. Initially the radius is 1 m and the tangential velocity is 4 m/s. The string is subsequently let out gradually until the radius doubles to 2 m. There are no frictional or resistive forces...

These are kind of my own thoughts. Does the theory of relativity disagree with any of these? When a spinning disc is heated, the spinning rate decreases, and spinning energy is being converted into additional heat. When a spinning disc is accelerated linearly, the spinning rate decreases, and...

Homework Statement Consider a bead of mass m sliding without friction on a wire that is bent in the shape of a parabola and is being spun with constant angular velocity ω about its vertical axis. Use cylindrical polar coordinates and let the equation of the parabola be ##z = kρ^{2}##. Write...

One of the classical consequences of relativity is that if someone travels far away from Earth and comes back, he would have aged less than people here (acceleration and thus changing frames of reference being the reason.) So, why wouldn't this work also for shorter distances? If someone runs...

Homework Statement I am just wondering, in Griffiths text, he solves this problem for a spinning shell. He states that the problem is easier if you tilt the sphere so it is spinning in the xz plane. Homework Equations When solving for the current density, Griffiths writes, $$...

Homework Statement A bowl has a hemispherical inside surface with radius R = 15 cm, and is sitting in the exact center of a spinning table that completes one full turn in 0.72 s. A small marble is dropped into the bowl. After the marble has stopped rolling around, it will come to rest...

I'm trying to understand the spinning egg phenomenon. That is, why does a hardboiled egg (or any solid ellipsoid) "stand on end" when spun at high velocities. Upon searching the web I found one site written by physicist Rod Cross in Sydney who tried to give a simple, intuitive explanation...

Homework Statement The Attempt at a Solution 7 Part(a) It can be seen that Eα > Emin, so ue is always bounded below Eα. 7 Part (b) It can be seen that for α = 1/2, Eα = Emin = -1/4. Thus for α < 1/2, the mass will start to drop. What puzzles me is how do you explain...

I have several questions about the motion of spinning coins. I won't get to them all in this post, but hopefully some of you can help get me started. (Note: I am a mathematician, not a physicist - that might help color your responses.) First I want to think about spinning an idealized penny...

In the spinning cylinder room example mentioned in relativity, where the nearest distance between 2 point is actually curved line.. and light take a straight pass right, which is farer than the curved line due to time dilation in the middle of the room due to a smaller acceleration than side of...

Homework Statement A turntable of radius "r" is spinning counterclockwise at an initial rate of ω. at t=0, its rotation rate begins to slow at a steady pace. the rotation finally stops at t=T. At what time during the time interval 0<t<T was the magnitude of the centripetal acceleration of a...

Homework Statement I'm supposed to find the time taken for the disk to slow down from ω0 to (1/2)ω0...Here's what I've done: Since on each side of the disk there is current flowing into the centre, each side experiences a force F, so the net torque on the system = 2Fa. Then I can find...

Every time I see a SF pic which has some simulated gravity by spinning I can't imagine this actually working. The latest SF I watched (mission to mars) had a wide rotating cillinder somewhere in the middle of a much longer cillinder which formed the main ship. Now imagine yourself moving from...

I have a 36" OD aluminum drum within another 48" OD aluminum drum creating 6” channel between the two diameters. The total height of the drum assembly is 16” This design project that I am working on requires me to fill this channel up with 12” of water which equates to about 342.5 lbs of water...

Hi all, I was wondering if one on you could answer this question. Imagine a person standing on a spinning merry go round. The friction exerted by the floor is the centrifugal force that keeps the person spinning in a circle. As the speed is building up, the person needs to lean back more...

Homework Statement A 75 gram ruler is evenly placed between two cylinders spinning clockwise on the left and counter clockwise on the right. The coefficient of friction between the ruler and the spinning cylinders is 0.2. You push the ruler to the right by 0.12 meters. It returns to you by...

Homework Statement http://i50.tinypic.com/mmws94.png Homework Equations The Attempt at a Solution 1. Angular momentum is constant; J = constant 2. Total energy is constant; E = constant Not sure why I am ending up with a 2gr instead..as U = ∫ f dr = ∫ mg dr

Hello dear physicists :) I have to admit it's been a long time since I studied physics in the university. And Sorry to disturb you with this video. Of course it is a very bad ad for Camry and the Saudi driving: But what catches my attention is how can the car spin that "violently"...

Hi everyone! I'm struggling to get my head around a calculation having not done any physics studies for 10 years - My brain is a little rusty. Please consider the following scenario: Railway trucks (railroad cars) are shunted around a yard using a tractor (Its a farm tractor on rubber tyres)...

They have the spin top magnet that you spin on top of a platform, which by effect causes it to appear to float. Is the effect any different if you spin the platform instead?

My question is about the strength of magnets and how the strength is affected when you spin a magnet. When I use my meter to read the gauss of a permanent magnet I don't get much of a reading at all. However, when I spin the magnet the reading becomes very strong bouncing the needle quite high...