# What is the required torque to rotate a 50mm aluminimum plate of weight 100g?

I have a aluminium plate of radius 50mm and thickness 4mm. How much torque is needed to rotate it?

In case additional information is required :

I have a RS 380 motor, but I guess torque required is irrespective of motor. How do you calculate torque of other round plate sizes? Like 60mm or 55mm.

What is approximatively the exact torque for 50mm?

[![motor][2]][2]

• Will the plate be attached to the motor and hang in midair? Or will it be touching something else, which would generate friction? If it's suspended in midair, then any amount of torque supplied by any motor would be sufficient to rotate the plate. Obviously, a larger motor will impart a greater rotational acceleration to the plate.
– Wasabi
Jul 22 '16 at 18:27
• The required acceleration is the key piece of information you need to answer this question, assuming nothing else is attached to the motor. Jul 22 '16 at 21:08
• As @Ethan48 points out, $\tau=I\alpha$, where $I$ depends on the geometry, $\tau$ is the torque, and $\alpha$ is the required angular acceleration. Without the latter information, torque has little meaning. Jul 23 '16 at 6:00
• Along what axis do you want to rotate it? How fast? How much acceleration? Is there any drag (friction) on it? Jul 23 '16 at 15:33
• @Wasabi a hole will be made in the center of the plate and attached to motor, and yes it will be rotated in mid air. No it won't touch anything else. I want to rotate the plate at 5000rpm , and in case if this detail is required : i am just letting you know,that the motor has a top speed of 18000. For motor details i guess Google would suffice. Would it need other detail. pls reply me. Jul 23 '16 at 19:07

Force is required to accelerate mass and overcome friction force. So the torque required in steady rpm only as big as the friction.

• right, note at 5000rpm the air drag will be substantial. googling "aerodynamic drag spinning disk" might proove fruitful Jul 31 '16 at 15:11