# Power calculations for a motor spinning a turntable

• mapika123
In summary: Or perhaps even some reduction, because the disc will be rotating more slowly than the one with a smaller radius.So I'd say no, you don't need more power. But the reasons are obscure.In summary, the power needed to maintain constant rotation of a turntable is not directly related to the speed, mass, or size of the turntable. It depends on factors such as axial friction and air resistance, which may vary. Therefore, doubling the diameter of the turntable may not necessarily require a motor with double the power.
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.

mapika123 said:
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?

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.

berkeman
mapika123 said:
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.

## 1. What is a power calculation for a motor spinning a turntable?

A power calculation for a motor spinning a turntable is a mathematical process that determines the amount of power needed to rotate the turntable at a desired speed and torque.

## 2. How is power calculated for a motor spinning a turntable?

Power is calculated by multiplying the torque required to rotate the turntable by the rotational speed of the motor. This can be expressed as P = T x ω, where P is power, T is torque, and ω is rotational speed.

## 3. What factors affect the power calculation for a motor spinning a turntable?

The power calculation is affected by various factors such as the weight and diameter of the turntable, the type and efficiency of the motor, and the desired speed and torque of rotation.

## 4. Why is it important to perform power calculations for a motor spinning a turntable?

Performing power calculations ensures that the motor is capable of providing enough power to rotate the turntable at the desired speed and torque. This helps in selecting the right motor for the application and prevents motor burnout or failure.

## 5. Can power calculations be used to optimize the performance of a motor spinning a turntable?

Yes, power calculations can be used to optimize the performance of a motor spinning a turntable by determining the most efficient combination of speed and torque for the motor. This can help in reducing energy consumption and improving the overall performance of the turntable.

• Engineering and Comp Sci Homework Help
Replies
7
Views
3K
• General Engineering
Replies
11
Views
2K
• Introductory Physics Homework Help
Replies
16
Views
3K
• Electrical Engineering
Replies
2
Views
1K
• Mechanical Engineering
Replies
19
Views
2K
• Mechanical Engineering
Replies
4
Views
2K
• Mechanics
Replies
7
Views
2K
• Introductory Physics Homework Help
Replies
4
Views
1K
• Mechanical Engineering
Replies
3
Views
3K
• Mechanical Engineering
Replies
34
Views
2K