Suppose a meteor is attracted by Earth's gravity. $m$ is the mass of the meteor, $v_t$ is the tangential velocity of the meteor, $v_n$ is the radial velocity of the meteor, $\vec F$ is the gravitational force between them At this time, if $\vec F>m \frac{v_t^2}{r}$. Then the meteor will eventually fall on the earth. As the radius $r$ gradually becomes smaller, $\vec F$ will move in the radial direction. Doing work, $\dot{v}_n$ starts to increase, and $\vec F$ does not do work in the tangential direction, so $\dot{v}_t$ always unchanged, in the formula $L=m\left[\vec r \times\left(\dot{\vec v}_t+\dot{\vec v}_n\right)\right]$, $\vec r \times \dot{\vec v_{n}}$ is always 0, so angular momentum is conserved,