In simple harmonic motion (SHM), the quantity that remains constant is the time period. The time period is the time taken for one complete cycle of the motion, which includes moving from one extreme point to another and back again. It is denoted by the symbol T.
In SHM, the other quantities such as the amplitude, acceleration, and speed are not constant throughout the motion and vary depending on the position of the oscillating object within the cycle.
Amplitude: The amplitude (A) in SHM represents the maximum displacement or distance from the equilibrium position. It remains constant throughout the motion of the system as long as the system is not affected by any external factors.
Acceleration: The acceleration (a) in SHM is not constant. It varies with the displacement from the equilibrium position. It is maximum at the extreme points (amplitude) and zero at the equilibrium position. The magnitude of the acceleration increases as the object moves away from the equilibrium position.
Speed: The speed (v) in SHM is not constant either. It varies with the displacement from the equilibrium position. The speed is maximum at the equilibrium position and decreases as the object moves away from it. The speed is zero at the extreme points (amplitude).
It's worth noting that although amplitude, acceleration, and speed are not constant in SHM, they are related to each other and change in a predictable manner as the oscillating object moves through its cycle. The time period, however, remains constant and defines the characteristic frequency of the oscillation.