For a point rotating around an origin:
![[angular_momentum.jpg]]
In the diagram the p vector is the momentum, i.e. the velocity times the mass.

## Moment of inertia $I$ is rotational mass
$$I = \sum mr^2$$It measures how strongly an object resists changes in its rotation

* Large $I$ → harder to start, stop, or alter rotation
- Small $I$ → easier to change rotation

It depends on **mass distribution**, not just mass:
Mass farther from the axis increases $I$ greatly.

**Gyroscope connection:**
$$L=I\omega$$
Bigger $I$  → larger angular momentum at the same spin rate → harder to tilt or redirect.
Can be thought of as: moment of inertia helps determine how “stubborn” a spinning object feels.

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