Concept of moment of inertia (A-level only) Flashcards – AQA A-level Physics (7408)

What does moment of inertia measure about a specified rotation axis?

It measures how mass is distributed relative to the axis, describing resistance to changes in rotational motion about that axis.

What is the moment of inertia of a point mass $m$ at perpendicular distance $r$ from the rotation axis?

$I = mr^2$

How is the moment of inertia of an extended object calculated from its mass elements?

$I = \sum_i m_i r_i^2$ where $r_i$ is the perpendicular distance of mass element $m_i$ from the axis.

What is the SI unit of moment of inertia?

$\mathrm{kg\,m^2}$

How does a mass element’s distance from the rotation axis affect its contribution to moment of inertia?

Its contribution is proportional to the square of its perpendicular distance from the axis.

How can changing the position or orientation of the rotation axis affect an object’s moment of inertia?

It can change the object’s moment of inertia.