# Could I measure the moment of inertia of a fidget spinner by making it the bob of a pendulum? How?

##### 1 Answer

Dec 11, 2017

Your question is ambiguous and carry wrong assumptions....

#### Explanation:

Moment-of-inertia, is not like mass. Mass is unique. When we speak of moment-of-inertia we have to also state the axis of rotation too. The same object will have different moment-of-inertia depending on what we choose as the axis of rotation. That is why moment-of-inertia is a tensor while mass is just a scalar.

But if you meant finding the moment-of-inertia of the fidget spinner for the usual rotation axis (how it is usually rotated), then I cannot think of a way of finding that using the fidget as a bob of simple pendulum. In fact the simple pendulum's period is independent of its mass and depend on on its length and the gravitational field strength.