Which term defines the fluctuation of speed of a flywheelin termsof linear speeds?

A

$$\frac{2(v_1 - v_2)}{v_1 + v_2}$$

B

$$\frac{2(v_1 + v_2)}{v_1 - v_2}$$

C

$$\frac{v_1 + v_2}{2(v_1 - v_2)}$$

D

$$\frac{v_1 - v_2}{2(v_1 + v_2)}$$