What limits the speed at which a metal ball can be made to rotate suspended in vacuum

[Justonium]

Apparently the fastest an object has ever been made to spin is only 23 million rpm. What is preventing us from making things spin faster, and maybe even approach the speed of light? If an object is magnetically suspended in a vacuum, I see no limiting factor. The only objects ever made to approach the speed of light have just been subatomic particles spun around a circular circuit of tube. When spinning an object with significant mass, however, the circuit of tube poses a huge limit to speeds attainable because the object's centrifugal force would be to great to hold in, but if it is spinning stationary, I see no limit to how fast electromagnets could accelerate it.

[swansont]

The object itself may be the limit, because of the forces needed to hold it together.

[Phi for All]

Impurities and irregularities in the metal ball and lack of access to unlimited energy, perhaps?

[Sisyphus]

An object spinning around its own center still has a centrifugal effect trying to rip it apart. An atom on the edge of that ball is still moving in a circle, and so the faster you spin it the greater its constant acceleration, the greater the forces acting on it. Thus it can't spin any faster than the point at which that force is greater than the molecular bonds holding it together.

[Sha31]

Apparently the fastest an object has ever been made to spin is only 23 million rpm. What is preventing us from making things spin faster, and maybe even approach the speed of light? If an object is magnetically suspended in a vacuum, I see no limiting factor. The only objects ever made to approach the speed of light have just been subatomic particles spun around a circular circuit of tube. When spinning an object with significant mass, however, the circuit of tube poses a huge limit to speeds attainable because the object's centrifugal force would be to great to hold in, but if it is spinning stationary, I see no limit to how fast electromagnets could accelerate it.

 

Where did you get information about 23mil rpm?

How much is that when converted to linear velocity?

 

Other than ball falling apart there should be no other limits. Actually, it should even keep its velocity indefinitely... perhaps even speed up as it gets lighter due to radiation.

[Justonium]

Where did you get information about 23mil rpm?

How much is that when converted to linear velocity?

 

Other than ball falling apart there should be no other limits. Actually, it should even keep its velocity indefinitely... perhaps even speed up as it gets lighter due to radiation.

 

Somebody said 23 million rpm done on a steel ball in a vacuum on yahoo answers, but I couldn't find the statistic myself. What do you mean about radiation? Like atoms flying off due to extreme centrifugal force? Oh, and sorry, yeah, because I couldn't track the 23 million rpm statistic I can't get the radius of the ball to calculate the linear velocity. I wonder what the max linear velocity ever achieved is.

Gosh it would be a disaster if one of the balls used in these experiments reached a speed high enough to rip itself apart.

[John Cuthber]

You may have noticed that CD roms used to run at the same speed as audio players but they gradually worked out ways to get them faster and faster. However, once they got to about 50 times, the stopped trying to speed them up. The limiting factor hese is that a CD will tear itself apart if you spin it much faster than that.

CDs are made from polycarbonate which is fairly light and very strong. If you made them smaller you could spin them faster. I don't know what they spun up to 23 million RPM but I bet it was small.

Of course, the smaller it is the lower the tangential velocity for a given rotational speed so the urther from the speed of light you get.

[insane_alien]

it was Jesse Beams who done the 23millionRPM expeiment. it was a 0.8mm diameter steel ball and was done in 1946.

[ydoaPs]

How much is that when converted to linear velocity?

 

Linear velocity of which part? It's different at each point along the radius.

[Justonium]

it was Jesse Beams who done the 23millionRPM expeiment. it was a 0.8mm diameter steel ball and was done in 1946.

 

Thanks, now I can read up on that experiment.

---

Merged post follows:

Consecutive posts merged

Linear velocity of which part? It's different at each point along the radius.

 

The farthest point from the axis; I'm kind of curious to see the fastest man can make a significant amount of matter travel in circles in a small space. And now that I know it was .8mm in diameter, I can calculate that the fastest part of the steel ball was traveling at a linear velocity of.... ohmyghosh, only 960 meters per second. I wonder what size ball will allow the greatest energy density to be stored in its inertia without destroying the ball.

Edited December 18, 2009 by Justonium
Consecutive posts merged.

[Sisyphus]

 

The farthest point from the axis; I'm kind of curious to see the fastest man can make a significant amount of matter travel in circles in a small space. And now that I know it was .8mm in diameter, I can calculate that the fastest part of the steel ball was traveling at a linear velocity of.... ohmyghosh, only 960 meters per second. I wonder what size ball will allow the greatest energy density to be stored in its inertia without destroying the ball.

 

I would say an extremely large ball would have a higher energy density overall, since you could have a much higher average linear velocity with fewer RPMs.

 

The limiting factor isn't going to be linear velocity, it's going to be centripetal acceleration. a=v^2/r

[Justonium]

I would say an extremely large ball would have a higher energy density overall, since you could have a much higher average linear velocity with fewer RPMs.

 

The limiting factor isn't going to be linear velocity, it's going to be centripetal acceleration. a=v^2/r

 

Yeah, I understand that the limiting factor is the strength of the ball to hold itself together; I'm just saying that I wonder what size of a ball would have the maximum possible energy density in it's inertia before shattering. Too big of a ball would make the centrifugal force too great to hold in at too low speeds. By the way, what I mean by energy density is the kinetic energy per mass of ball. Also, if the optimum radius is known, this would best be taken advantage of by using a rotating cylinder, because that radius would be present everywhere.

 

The reason I brought this topic up is because I'm wondering if a spinning object suspended in vacuum could make for better energy storage than the currently used chemical batteries. It would also be a lot more convenient to store and release energy, and would never degrade.

[Zolar V]

i would think that the greater the mass the greator the energy density. just look at the earth. at some point i would think that gravity produced by mass would over come centripital forces acting on the atoms.

[DJBruce]

i would think that the greater the mass the greator the energy density. just look at the earth. at some point i would think that gravity produced by mass would over come centripital forces acting on the atoms.

 

At the atomic scale the force that is going to have to be overcame is not gravity, but that of electromagnetism in the bonds between the atoms. So I am not sure how mass would overcome the centripetal force.

[Zolar V]

At the atomic scale the force that is going to have to be overcame is not gravity, but that of electromagnetism in the bonds between the atoms. So I am not sure how mass would overcome the centripetal force.

 

hmm, lets find a wonderfull example. ok i got one. A black hole. here you have gravitational force over comming all other forces.

[Sha31]

The reason I brought this topic up is because I'm wondering if a spinning object suspended in vacuum could make for better energy storage than the currently used chemical batteries. It would also be a lot more convenient to store and release energy' date=' and would never degrade.[/quote']

 

That's interesting, though I don't think it would work for portable batteries as these would not be very shock-resistant. Also, strong magnetic fields would not be very welcomed around electronic equipment.

 

So, I suppose you would feed in electric energy to increase the spin, then later you would use this spin to get back electricity? How would you do the conversion?

[Mr Skeptic]

I wonder what size ball will allow the greatest energy density to be stored in its inertia without destroying the ball.

 

A ring shape, actually. Bigger would be better, except that for safety it needs to be contained and the bigger container would weigh a lot.

[insane_alien]

mr skeptic, surely a sphere would be better than a ring as it would be structurally stronger and could fit the ring inside it. you could also go for a cylinder as well.

[Justonium]

That's interesting, though I don't think it would work for portable batteries as these would not be very shock-resistant. Also, strong magnetic fields would not be very welcomed around electronic equipment.

 

So, I suppose you would feed in electric energy to increase the spin, then later you would use this spin to get back electricity? How would you do the conversion?

 

The technology to store and release energy from a spinning ball already exists; it uses similar principles as an electric motor and an electric generator.

 

By the way, I see a lot of people saying the bigger it is, the more energy storage, but I disagree, because a very large sphere would have incredible centrifugal force that would tear it apart when the core of it would be traveling at relatively lower velocities. I know that once you get really really big, gravity takes over and holds it in, but is that is irrelevant in this thread because it is not practical to use here on earth.

[insane_alien]

Justonium, big things hold energy easier because they don't have to spin as fast in order to hold that amount of energy.

 

to make this example very very clear i'm going to take it to ridiculous levels.

 

lets take the earth, the centripetal acceleration necessary for it to hold together is quite tiny, so it could happen without gravity. if has a LOT of energy stored alothough it is rotating quite slowly.

 

if i were to take that 0.8mm diameter ball at 23million RPM what do you think its energy is in comparison to the earths?

 

if you thought 'not much' then you'd be right.

 

its true, in theory you could impart the same rotational energy the earth has on that little ball but it would require it to be made of unobtanium and ultrahigh vaccuuums for its storage and all sorts of fancy technological wizardry to be able to spin it up and extract the energy(modern tech is too slow to do this).

 

big stuff can hold more energy. nuff said.

[Mr Skeptic]

Justonium, at any speed a larger object will have less centrifugal force than a smaller object, because there will be less curvature in the trajectory. The centrifugal force is inversely proportional to the radius, and directly proportional to the square of the velocity. The reason a smaller object can be spun to more RPMs is because the velocity is directly related to both radius and angular velocity.

[Justonium]

Justonium, big things hold energy easier because they don't have to spin as fast in order to hold that amount of energy.

 

to make this example very very clear i'm going to take it to ridiculous levels.

 

lets take the earth, the centripetal acceleration necessary for it to hold together is quite tiny, so it could happen without gravity. if has a LOT of energy stored alothough it is rotating quite slowly.

 

if i were to take that 0.8mm diameter ball at 23million RPM what do you think its energy is in comparison to the earths?

 

if you thought 'not much' then you'd be right.

 

its true, in theory you could impart the same rotational energy the earth has on that little ball but it would require it to be made of unobtanium and ultrahigh vaccuuums for its storage and all sorts of fancy technological wizardry to be able to spin it up and extract the energy(modern tech is too slow to do this).

 

big stuff can hold more energy. nuff said.

 

I'm not talking total energy, I'm talking energy density. The earth weighs a lot compared to the energy stored in its rotation. The earth would probably have much lower energy per mass than a .8mm steel ball going at 23 million rpm. Sorry if I was unclear.

---

Merged post follows:

Consecutive posts merged

Basically, what I want to know is this: when comparing 2 disks of different diameters, both spinning at speeds at which the outer layers of each one have equal centrifugal acceleration, which disc's atoms will have a higher average velocity squared? I'm a noob at physics i know.

 

Argh, the centrifugal acceleration of the outer layer of the disc wouldn't accurately represent the stress pulling the entire disc apart. This is a complicated problem.

Edited December 29, 2009 by Justonium
Consecutive posts merged.

[Mr Skeptic]

Basically, what I want to know is this: when comparing 2 disks of different diameters, both spinning at speeds at which the outer layers of each one have equal centrifugal acceleration, which disc's atoms will have a higher average velocity squared? I'm a noob at physics i know.

 

Argh, the centrifugal acceleration of the outer layer of the disc wouldn't accurately represent the stress pulling the entire disc apart. This is a complicated problem.

 

This is why I suggested a ring (hollow cylinder to be exact). That way we can assume most of the mass is on the edge, which as a bonus means we don't need calculus to calculate the energy and centrifugal force.

 

Now, the equation for centrifugal force is [math]F = \frac{mv^2}{r}[/math] and for kinetic energy is [math]KE = \frac{1}{2}mv^2[/math]. From this it is obvious that the larger you get your object, the more kinetic energy it can hold per unit centrifugal force. Now, the other problem is if you don't want to assume a ring, ie, you need stuff in roughly a disk shape for support, then there would be a limit to the size that would be most efficient, since eventually your support mass would be very large for a large object.

[Justonium]

Mr Skeptic, are you sure there would be a limit to the sized disk that would be most efficient? Either there is, and this would vary for different materials, or there isn't and the efficiency increases the bigger you get no matter what; this is what I want to be certain of.

[Mr Skeptic]

Basically, what I want to know is this: when comparing 2 disks of different diameters, both spinning at speeds at which the outer layers of each one have equal centrifugal acceleration, which disc's atoms will have a higher average velocity squared? I'm a noob at physics i know.

 

Under those conditions, the larger object would have a lower energy density, since the stuff inside would be moving slowly. However, as I pointed out, it will have a lower centrifugal force as well, since the centrifugal force decreases as size increases (for a given velocity). What I was talking about was higher energy per unit of centrifugal force.