# Where does the energy go? [duplicate]

Suppose a typical case of a girl dancing and after sometime changing her $$I$$ (moment of inertia to rotate) faster, my doubt is in this case there is a non-zero difference in initial and final total KE (in this case only rotational KE), why does it so?

• Possible duplicate: physics.stackexchange.com/q/45743 Nov 27 '21 at 11:13
• Yeah but now its cleared here too Nov 27 '21 at 11:17

The kinetic energy increases for the dancer after pulling her arms in (for example). That would decrease her moment of inertia, but from conservation of angular momentum, increase her angular velocity $$\omega$$.
$$K.E. = \frac{1}{2}I\omega^2$$