Chapter 4, Problem 68P

Figure 4.27 shows vertical accelerometer data from an iPhone that was dropped onto a pillow. The phone’s accelerometer, like all accelerometers, can’t distinguish gravity from acceleration, so it reads 1g when it’s not accelerating and 0g when it’s in free fall. Interpret the graph to determine (a) how long the phone was in free fall and therefore how far it fell, (b) how many times it bounced. (c) the maximum force the phone experienced, expressed in terms of its weight w, and (d) when it finally came completely to rest. (Note: The phone was held flat when dropped, with the screen up for protection. In that orientation, it recorded negative values for acceleration; the graph shows the corresponding positive values what would have been recorded had it fallen screen side down.)

FIGURE 4.27 Accelerometer data for Problem 68, taken with on iPhone. The accelerometer can’t distinguish gravity from acceleration, so what it actually measures is apparent weight divided by mass, expressed in units of g.