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Q.
When acrobat bends his body (assume no external torque)
System of Particles and Rotational Motion
Solution:
By the conservation of angular momentum, we know that $I \omega=$ constant.
As the acrobat bends his body, then moment of inertia $I$ will decrease and hence $\omega$ of acrobat will increase as no external torque is acting on the acrobat.
