## General Question

Asked by Ltryptophan (10724) May 10th, 2016

I have seen in science labs a magnetic machine that spins a capsule in a beaker to mix things. One puts the beaker on the machine, drops in a polarized magnetic capsule, and it spins.

How fast could a magnet spin in this way without some unwelcome result? I’m thinking actual revolutions per minute. I’m guessing that there may be a magnetic force, to centripetal force equation to use.

Thanks!

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Is this a centrifuge?

stanleybmanly (22357)

Like one of these Arduino stirrers.

I have heard of some stirrers at 1300 RPM.

@Tropical_Willie it doesn’t have to be arduino based, they are called magnetic stirrers I have now discovered. I found one at 1700 rpm’s. It doesn’t give me a technical answer to my question, but the top range could be nearby…

I am sure someone who is a physicist could easily come up with a formula based on known strength of magnetic forces applied to spinning conditions for a magnetic stir bar.

Ltryptophan (10724)

However quick the motor underneath moves.

Rarebear (25159)

@Rarebear I’m not so sure how they work. Are you suggesting that a magnet holds the bar in place while a motor beneath it spins the magnet? If that is the case, are you saying I could hook a 50hp motor to the magnet and get it up to as many RPM’s as the motor can handle without the magnetic bar in the beaker (sufficiently stabilized from vibrations, etc.) melting the glass underneath it, cracking the beaker, stopping the spin in exchange for random flipping, or some other undesired result….......

Ltryptophan (10724)

Yeah pretty much. If the beaker has a lot of friction it will fly off.

Rarebear (25159)

@Ltryptophan Most of them use a set of electro magnets in the base that generate a rotating magnetic field which spin the stirrer. If you turn it up too far the little magnet will start to dance around erratically and you won’t have a vortex anymore. I think this is what you are asking right? Depends on what you are stirring for how much becomes too much. It’s not likely a simple equation but you could probably derive a simple one experimentally to model the one you have by plotting curves for the fluids you are stirring. Just use excel to do a regression and spit out your equation. Each fluid will likely give you a slightly different curve as will air. Once you have those finding an equation based on properties of the materials being stirred should not be too hard.

To answer this question you need to know the name, make and model of the analyzer. Then simply contact the company for the information that you want.

gondwanalon (19065)

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