Torque and Power

BAZINGA! GA!

And initially to overcome the static inertia breakpoint.

1000 ft lbs

Think about it. How much torque and power does it need to keep our planet spinning?

It's clockwork.

What environment is it in? What are the characteristics of the fluid that surrounds it, if any? How rough is the cylinders surface? What are the dimensions of the cylinder? About what axis is the cylinder to be rotated?

Are there magnetic fields that permeate the space in which it is to spin? If so, how conductive is the material of the cylinder. Is the material ferromagnetic, ferrimagnetic, paramagnetic, or diamgnetic?

How is the cylinder supported? Are you to assume the gravity is typical for the surface of the earth?

How rigid is the cylinder?

If there an acceptable range for the answer you provide? Will your answer be compared to the outcome of some experiment?

If you don't have or cannot obtain enough data to accurately calculate it you could try building the experiment and measuring it instead and working the math and calculations backwards.

Ideally you should have a rough guess using the math available to you first and see how close you get.

It's a mild steel solid cylinder with dia 16 cm and thickness 6.3 cm. It is supported at both sides by ball bearings. Considering all the air resistance, gravity etc., what will be the power and torque required to rotate it at 30 rpm continuously. So I can select a suitable motor for it.

YOU are, "doing a project for High school".

Don't ask strangers to do your project for you.

It is your project and that means that you must determine "a suitable motor" after determining what forces are required.

You didn't read the rules!

"Do your own homework. CR4 is not a homework cheat site; however, if you have questions about understanding concepts or how a portion of a problem is derived, these types of questions will be accepted."

I want to know which formula to apply for it. If you know tell

NO!

Now that is just silly. You want us to give you straight forward replies that will lead you to the correct answer.....but you aren't even being straight with us about the cylinder in question.

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A solid steel cylinder of the dimensions you note, 16 cm diameter and 6.3 cm height will not weigh 10 kg.

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You haven't provided the specifics necessary, and I doubt any high school would expect you to be able to calculate the air resistance and resistance of the bearings. You should experiment a little.

Pi x r² x h x density = 3.142 x 8 x 8 x 6.3 x 8 looks about right to me

My apologies. I should have double checked my head math. I had arrived at something the density of tungsten with that mass/volume.

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Mea culpa.

It all depends on the radius and how is mass is distributed in the cylinder (whats the actual radius of gyration.)

do it in space, it will definitely rotate continuously unless other wise deterred by an external force.

It's a mild steel solid cylinder with dia 16 cm and thickness 6.3 cm. It is supported at both sides by ball bearings. Considering all the air resistance, gravity etc., what will be the power and torque required to rotate it at 30 rpm continuously. So I can select a suitable motor for it.

As we've indicated before it's not keeping it running it's getting it up to speed that's the problem.

Buy a cheap record deck: figure out how to slow it from 33 rpm to 30 rpm.

Help it up to speed.

Use any motor capable of 30 rpm unloaded, that can overcome your friction. Don't worry about the torque. For economy, get the smallest miniature electric motor you can find.

Now no telling when the cylinder comes up to speed. Could be an hour, could be a week. That is a function of the torque.

See where this is going....

I like this one, much less theory involved. Answer is; no motor needed, therefore, no torque requirements.

I will give you one thing Sachin, you were not shy or clever about it. You straight up asked us to do your homework assignment. Balls baby!

Is your weight shaft mounted or circumference mounted?

What bearings are being employed or just bushings.

Is it driven from the center or from the edge.

Direct, reduction, belt, gear, magnetic drive.

Is it running in air or water or outerspace.

Is there any resistance in this setup.

How long do you want it to last.

What color is it.

How's that?

Truth is . . . provided a bunch of things to consider in a real-life situation. In college (ages ago) we made simplifying assumptions; in this case "frictionless." Therefore, power required is zero since you are not accelerating and nothing is resisting its current motion.

This depends on two main things: 1) How quickly you wish to accelerate the cylinder to its ultimate speed, and 2) How much friction there is in whatever bearings support it.

A clock motor or record turntable motor could be close to what you need.