The period of oscillation of a simple pendulum does not depend on the mass of the bob. By contrast, the period of a mass-spring system does depend on mass. For a mass-spring system, the mass still affects the inertia, but it does not cause the force. The spring (and its spring constant) is fully responsible for force.
Hereof, what affects the period of a mass on a spring?
The period of oscillation is, therefore, directly proportional to the mass and inversely proportional to the spring constant. A stiffer spring with a constant mass decreases the period of oscillation. Increasing the mass increases the period of oscillation.
How does the mass affect the period of a pendulum?
(Mass does not affect the pendulum's swing. The longer the length of string, the farther the pendulum falls; and therefore, the longer the period, or back and forth swing of the pendulum. The greater the amplitude, or angle, the farther the pendulum falls; and therefore, the longer the period.)
Why does the mass not affect the period of the pendulum?
The mass on a pendulum does not affect the swing because force and mass are proportional and when the mass increases so does the force. As the force increases so does the acceleration and along with gravity are the factors that affect the pendulum swing. Therefore, the mass does not affect the period of the pendulum.