Power calculations for a motor spinning a turntable

[mapika123]

Homework Statement

Physics question

Relevant Equations

Energy/power- w/speed

Hi, I have a 1 HP motor spinning a turntable (just a wheel) weighing 1kg, diameter 25cm speed 2000rpm. (Arbitrary specs). If I have to spin a turntable with the same weight (1kg) but double the diameter (50cm) at the same speed, would I necessarily need a motor with double the power (2 HP)? There is no load on the turntable, ( just spinning).

Thank you kindly.

 

[berkeman]

Homework Statement:: Physics question
Relevant Equations:: Energy/power- w/speed

Hi, I have a 1 HP motor spinning a turntable (just a wheel) weighing 1kg, diameter 25cm speed 2000rpm. (Arbitrary specs). If I have to spin a turntable with the same weight (1kg) but double the diameter (50cm) at the same speed, would I necessarily need a motor with double the power (2 HP)? There is no load on the turntable, ( just spinning).

Thank you kindly.

Welcome to PF.

Is this for homework? What equations do you know so far for spinning a circular disk?

And just to keep a disk spinning, all you have to do is overcome bearing friction. To accelerate it up to speed, that is where it takes more power.

Are you familiar with the equations involving the "Moment of Inertia" (MOI) of spinning objects?

 

[kuruman]

The power you need to maintain a certain speed depends on your losses. In the limit that no energy is lost while the turntable is spinning, you need no power to keep it spinning. That's Newton's first law.

Argh! @berkeman preempted me.

 

[haruspex]

Homework Statement:: Physics question
Relevant Equations:: Energy/power- w/speed

Hi, I have a 1 HP motor spinning a turntable (just a wheel) weighing 1kg, diameter 25cm speed 2000rpm. (Arbitrary specs). If I have to spin a turntable with the same weight (1kg) but double the diameter (50cm) at the same speed, would I necessarily need a motor with double the power (2 HP)? There is no load on the turntable, ( just spinning).

Thank you kindly.

The power needed for constant rotation is not related (much) to the speed, mass or size. It depends on axial friction and a bit on air resistance.
The axial friction may be proportional to the mass. The air resistance will be a bit more for the larger size, particularly because that will increase the tangential speed at the periphery.
So it's hard to say without knowing how much each resistance contributes. If we assume no axial friction and air resistance rises as the square of the linear speed at a given radius then for the disc as a whole it would rise as the fourth power of the radius ($\int kr^2\omega^2.2\pi r.dr$). But likely it is mostly axial friction, so you might see hardly any difference.