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Rotation

Classical mechanics doesn't just describe how an object's position behaves under external influences, but also how its orientation behaves. Using the same principles found in Newtonian mechanics, laws and relations governing rotation can also be derived. Please direct all your questions about moments of inertia, angular velocity, angular momentum, centripetal force, centrifugal force, torque, and spin here.

500 Questions

What is rotor meter?

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Is radius of gyration a constant quantity?

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No. Radius of gyration depends upon the axis of rotation of the body.

When the mass and the radius are held constant what happens to the centripetal force if the frequency of the rotation is increased?

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One formula to calculate centripetal acceleration is:

a = omega2r, where omega is the angular velocity.

Combining this with Newton's Second Law:

F=ma

you get:

F = m omega2 r

For completeness sake, omega (in radians per second) = 2 pi f (2 x pi x the frequency,

in revolutions / second). Thus, omega and the frequency are proportional.

As you can see, the force is proportional to the square of the angular velocity.

For example, doubling the frequency would cause double the angular velocity,

which would require an increase of the force by a factor of 4.

What is the constant of proportionality between torque and angular acceleration?

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The rotating object's moment of inertia.

Similar to Newton's Second Law, commonly quoted as "force = mass x acceleration", there is an equivalent law for rotational movement: "torque = moment of inertia x angular acceleration". The moment of inertia depends on the rotating object's mass and its exact shape - you can even have a different moment of inertia for the same shape, if the axis of rotation is changed. If you use SI units, and radians for angles (and therefore radians/second2 for angular acceleration), no further constants of proportionality are required.

Does the centripetal force act as an unbalanced force on the satellite in orbit?

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Yes. According to Newton's Second Law, there has to be an unbalanced force - otherwise, the satellite won't accelerate (in this case, change direction).

What is relation between linear velocity and angular velocity?

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velosity in circular path angular

What is repetitive force?

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How is the radius of rotation related to the centripetal force and angular velocity?

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Assuming that angles are measured in radians, and angular velocity in radians per second (this simplifies formulae):

Radius of rotation is unrelated to angular velocity.

Linear velocity = angular velocity x radius

Centripetal acceleration = velocity squared / radius

Centripetal acceleration = (angular velocity) squared x radius

Centripetal force = mass x acceleration = mass x (angular velocity) squared x radius

Why did my physics teacher make me write centrifugal force is a figment of my imagination and centripetal force is real?

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Because there is no centrifugal force. The force of circular motion is inward, thus centripetal. If you are on a car that makes a quick right turn, you feel a "centrifugal" force leftward. But in reality, it is the car making an acceleration to the center of the curve, which is to your right. What you feel is inertia, not a force.

What is clockwise and anticlockwise torque?

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Clockwise, top rotating to the right, and counterclockwise, top rotating to the left is only a perspective based on the position of the observer. The torque is the rotational force of the rotating object. Most often the perspective of the observer is from the driving end of a shaft facing the driven machine. The amount of torque at a given speed of the driving machine (engine or motor) is mechanically converted into work by the driven machine (generator, pump, compressor...etc.).

Are revolution and rotation the same?

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No, they aren't the same. Revolution is the object moving in a circular motion. Rotation is when the object stays in one place and spins around.

What is dimension of angular velocity?

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[ T-1 ] . Reciprocal time, from "degrees per second" .

The angle part of it is dimensionless.

What is the angular momentum of the 2.6 kg 5.6 cm diameter rotating disk.?

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Without knowing the angular speed, i.e. RPM or some such velocity, it is not possible to answer the question. Please restate the question, giving all of the required information.

Which will have the greater acceleration rolling down an incline plane- a large ball or a small ball?

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If they are both solid, and the incline is the same, the rate of acceleration will be the same.