## SAT Physics Subject Test

**Chapter 6 ****Curved and Rotational Motion**

**CONSERVATION OF ANGULAR MOMENTUM**

Newton’s second law says that

so if *F*_{net} = 0, then **p** is constant. This is conservation of linear momentum.

The rotational analog of this is

So if τ_{net} = 0, then **L** is constant. This is **conservation of angular momentum**. Basically, this law says that if the torques on a body balance so that the net torque is zero, then the body’s angular momentum can’t change.

The most common example of this phenomenon is when a figure skater spins. As the skater pulls her arms inward, she moves more of her mass closer to the rotation axis and decreases her rotational inertia, *I*. Since the external torque on her is negligible, her angular momentum must be conserved. Since *L* = *Iω*, a decrease in *ω* causes an increase in, and she spins faster.