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Moment Of Inertia Of A Solid Cylinder

Moment Of Inertia Of A Solid Cylinder

The Moment of Inertia (MI) measures how much an object resists changes in its rotational motion about a given axis. It plays a similar role in rotational motion as mass does in linear motion. A solid cylinder is a three-dimensional object with a circular cross-section and uniform mass distribution. The moment of inertia depends on the axis of rotation.

Moment of Inertia About Different Axes

Considering a cylinder of mass M, radius of base R, and length L. The following are the cases of moment of inertia for different axes:

Moment of Inertia About the Central Axis (Longitudinal Axis)

Derivation:
Consider a thin solid cylinder and divide it into many thin circular discs stacked along its length.

The moment of inertia of one disc about its central axis (perpendicular to the flat face) is:

formula

Since all discs have the same radius and are aligned, the total moment of inertia is:

formula

Moment of Inertia About an Axis Perpendicular to the Length and Passing Through the Centre

We use the Perpendicular Axis Theorem for each disc element. For a disc:

formula

Integrating along the length or directly using the formula for a solid cylinder:

formula

Moment of Inertia About an Axis Through the Rim, Parallel to the Central Axis

formula

Formulae at a Glance

Shape Axis Moment of Inertia
Solid Cylinder Central axis (longitudinal) formula
Solid Cylinder Perpendicular to length, through centre formula
Solid Cylinder Parallel to central axis, through rim formula

Applications

  • Flywheels – Store rotational kinetic energy for smooth power delivery in engines.
  • Electric motor rotors – Require accurate moment of inertia calculation for speed control and torque efficiency.
  • Rolling objects – Physics of rolling cylinders without slipping depends on the moment of inertia.
  • Drums and rollers – Used in printing presses and conveyor belts.
  • Gas cylinders – Stability during rotation and movement.
  • Wheels and rollers – Common in vehicles and heavy machinery for motion control.

Summing Up

formula

Frequently Asked Questions

Q1. Does a solid cylinder have the same moment of inertia as a hollow cylinder?

No, a hollow cylinder has a greater moment of inertia for the same mass and radius because its mass is farther from the axis.

Q2. Which has a smaller moment of inertia, a cylinder with a small radius or a large radius?

A smaller radius gives a smaller moment of inertia, making it easier to rotate.

Q3. A solid cylinder has mass M = 4 kg and radius R = 0.5 m. Find its moment of inertia about the central axis.

formula

Q4. A solid cylinder has mass M = 10 kg, radius R = 0.2 m, and length L = 1 m. Find the moment of inertia about an axis perpendicular to its length and passing through the centre.

formula

 

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