Final answer:
The quantity oscillating in a pendulum system is the angular displacement. The oscillation frequency can be changed by altering the length of the pendulum or the local gravitational acceleration.
Step-by-step explanation:
In the case of a pendulum system, the quantity that is oscillating in time is the angular displacement of the pendulum bob from its equilibrium position. There are specific physical parameters you could change in the system that would affect the oscillation frequency. The primary factors that determine the frequency of a pendulum's oscillation are its length and the acceleration due to gravity.
The mass of the pendulum bob does not affect the frequency of a simple pendulum's oscillations. In a simple harmonic oscillator, such as a mass-spring system, the frequency can be altered by changing the mass of the system or the spring constant (stiffness). Therefore, to change the oscillation frequency in a pendulum, you would modify the length of the pendulum or adjust the local gravitational acceleration (which is practical only in a theoretical or experimental context, such as using a different planet's gravity in a simulation).