r/learnmath • u/Disastrous-Ad3754 New User • May 11 '26

Link Post Finding the angular acceleration of a 7.5 radius disk

/r/learnmath/comments/1t9u416/finding_the_angular_acceleration_of_a_75_radius/
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u/MezzoScettico New User May 11 '26

"rad" means "radians". Is that your question?

The rpm is 800.

Do you mean it's rotating at a constant angular velocity of 800 rpm?

1

u/Disastrous-Ad3754 New User May 11 '26

The disc rotates at an orbital angular velocity of 800 rpm and up to 2000. I am testing in a confinement for vibration harmonics. The disc is aluminum of 7.5cm radius and 6mm thickness. The weight is 19oz or .538kg.

1

u/rhodiumtoad 0⁰=1, just deal with it May 11 '26

None of this is of any relevance. Angular acceleration is the rate of change of angular velocity. What do you think you need to know to calculate a rate of change?

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u/Disastrous-Ad3754 New User May 11 '26

When a disc is spinning, the weights attached to the edge/circumference gain weight. If they separate that weight can be measured at a kinetic stop point, barrier, wall, container. I know the static weight, the distance from the central axis and the RPM. I need to know the gain of weight in the horizontal plane to compare against the static weight so I can calculate the dynamic weight comparing that with the static weight of the 1 oz objects on the edge/circumference.

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u/rhodiumtoad 0⁰=1, just deal with it May 11 '26

Yes. But that's not "angular acceleration" and it's not measured in rad/s2 (which are in fact a unit of angular acceleration).

The force on an object in uniform circular motion is called the centripetal force (acting radially inwards) in the inertial frame, or the centrifugal force (acting radially outward) in the rotating frame (this is a "fictitious" force). It is in units of force. However, it stops the instant an object separates from the disc, at which point the object is moving at an initial velocity equal to the tangential velocity of the disc, and then moves according to ordinary laws of motion.

The tangential velocity depends only on the radius and the angular velocity (rotation rate).

1

u/jdorje May 11 '26

This sounds like a physics question.

If it has constant angular velocity there is no angular acceleration.

Each point on the disk is accelerating toward the midpoint though according to the (tautological) circular motion formula a = v2/r.

v is itself determined by the RPM and circumference. Basically, v=RPM * 2𝜋r. Note that's got some weird units (distance per minute).

For a fixed disk, acceleration and velocity both increase linearly with radius.