AP Physics 1 Energies in a System Question Bank

(12 points, suggested time 25 minutes) Food scientists have created a new oil. At room temperature, the oil is a liquid. As the oil gets colder, however, it stiffens (thickens) into a sticky gel. To explore the properties of the oil, the scientists fill a container with the oil to a height D, as shown in the figure above on the left. They drop a small steel ball of mass M from rest at the top of the oil. Using video to capture the ball's motion, the scientists calculate $E_{\text {lost }}$, the mechanical energy lost by the ball-Earth system from the time the ball enters the oil to the time just before the ball strikes the bottom of the container. The scientists also define the "stiffness" S of the oil as a quantity proportional to the force required to move a rod through the oil at a standard constant speed. The scientists calculate $E_{\text {lost }}$ and S at several different temperatures, ranging from room temperature to the lowest temperature at which the ball still falls through the oil. The graph above on the right shows $E_{\text {lost }}$ as a function of S for the calculated data points and a best-fit curve.

(a) Give a physical reason why the curve in the graph would not reach the vertical $\left(E_{\text {lost }}\right)$ axis even if the scientists had taken data over a broader range of temperatures.