The graph of height as a function of time for an object falling straight down is a parabola. The average velocity of this falling object approaches its instantaneous velocity as the time interval tends to zero. Interpreting this geometrically on the parabola, the slope of a secant line approaches the slope of the tangent to the curve.
Neglecting air resistance, the object is falling to the ground from an initial height of 20 feet with an initial velocity of 0 feet/sec. Slide time to approximate the instantaneous velocity of a falling object either 0.2, 0.6, or 1 second after being dropped.