Parallel-axis theorem, torque

• If the object is just a few compact chunks of mass, use
  
• If the object is extended, with a non-uniform density, you'll need to break the object into simple little pieces and add up the moment of inertia from each piece:
  
• If the object is a simple geometrical shape, AND it has a constant density, AND it is rotating around its center, you can look it up in a table of common shapes; any textbook will have such a table, or you could use this table of moments of inertia (PDF) or this copy of the table in PNG format.
• If the object is a simple geometrical shape, AND it has a constant density, but it is NOT rotating around its center, you can use the table in your textbook and the parallel axis theorem . Read Section 9.5 or this very brief explanation .
  • Whirling a balloon
  • Example of parallel-axis theorem: moment of inertia of a square plate

• Introduction to Torque
• some analogies between linear and rotational quantities
• Stop the Earth!

Copyright © Michael Richmond. This work is licensed under a Creative Commons License.