In the given context, the function f(t) = 13.5 sin(5 * 2πt) + 20 describes the vertical position of a point on the bicycle wheel, in inches, at any given time t in seconds.
The amplitude of the sine function, which is 13.5 in this case, determines the maximum displacement or distance of the point on the wheel from its equilibrium position (the midline).
In other words, the point on the wheel moves up and down by a maximum distance of 13.5 inches from the center of the wheel as it spins. This means that the diameter of the wheel is twice the amplitude, which is 27 inches.
So, 13.5 is the amplitude of the sine function and represents the maximum displacement of the point on the bicycle wheel from its equilibrium position.