Physics
Rotational Inertia
Quick fact
A figure skater can change their rotation speed by pulling in their arms, which reduces their rotational inertia.
Why this is interesting
Have you ever wondered why it's harder to spin a merry-go-round when more people are on it? That’s rotational inertia in action.
Read the full explanation
Understanding Rotational Inertia
Rotational inertia is the tendency of an object to keep rotating unless acted upon by a force. It depends on how mass is distributed around the axis of rotation—more mass farther from the axis makes it harder to spin.
A deeper explanation
Rotational inertia, also called moment of inertia, describes how difficult it is to change an object’s rotational motion. The further the mass is from the axis, the greater the resistance to angular acceleration. This principle is key in designing everything from bicycle wheels to space satellites.