Many smartphones have an inbuilt accelerometer that can detect very small accelerations. Install an app, such as Phyphox (phyphox.org) and open 'Accelerometer' (without g). Note the readings when (i) the phone is on an outstretched palm, and (ii) the phone is kept on the floor. What differences do you observe? What does this tell you about motion and acceleration in real situations?
What differences do you observe between the readings when the phone is on an outstretched palm and when kept on the floor?
When the phone is on an outstretched palm, the accelerometer detects tiny involuntary movements (small fluctuations in readings). When the phone is kept on the floor, these fluctuations are significantly reduced or absent, showing more stable readings.
This tells us that in real situations, even when we think an object is stationary, there can be small accelerations due to involuntary movements. These tiny movements are significant enough to be detected by sensitive instruments and are even studied in medical research for conditions like movement disorders. It shows that perfect rest is difficult to achieve in practice.
Explanation
The textbook context mentions that such tiny involuntary movements are studied in medical research for movement disorders. When the phone is on an outstretched palm, the human hand naturally has small tremors/involuntary movements that the sensitive accelerometer can detect. On the floor, these human-induced movements are absent. This demonstrates that in real situations, objects we consider 'at rest' may still experience small accelerations, and that acceleration isn't just about large, visible changes in motion but also includes these minute, involuntary movements.