pi/2*(2n-1) radians.
Well their are lots of stuff to hypnotize someone you may not even know it but you can hypnotize someone by your eyes voice and or use a pendulumn and swing it from side to side.
at the center of the earth, simple pendulmn has not any gravitational force(if we thought,the earth is an etended object) so at the center the gravitational acceleation is about 'zero' and that's why pendulumn's time period is 'infinite'.
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