Does the material (of a pendulum), affect the period of that pendulum?

The only theoretical determinant of a pendulum's period is the length of the pendulum arm, but it's not all that simple. This approximation only works at small angles because of a sine relationship (learned in PHYS 109 lab experiment). In reality, the density of the pendulum arm and counterweight matter, as that will change the center of m of the pendulum, thus altering its frequency. Also, even if the m and point of balance were to remain fixed after changing the material, the wind resistance would change, thus altering the frequency. If you want to test this, make a simple pendulum, using first a small steel ball, then a Styrofoam ball of the same SIZE, and then a Styrofoam block (with the same effective point of balance) of the same M. The frequency will be different for all three (although it might be hard to tell with the last one, as the only difference should be wind resistance)