If the air resistance and other usually neglected perturbations are
unchanged. the answer is
nothing.
Now if you add mass to an already swinging pendulum the amplitude will
decrease (but not the period within the small angle region)
Alex. F. Burr
In a message dated 10/5/2011 1:09:01 P.M. Mountain Daylight Time,
bernardcleyet@redshift.com writes:
what happens to the amplitude of a pendulum clock when the bob's mass is
increased (without changing the CoM).