Apparent weight in an elevator
When an elevator starts or stops, the scale "lies".
The scale reading equals the normal force it exerts on the person. When the acceleration points upward (speeding up on the way up or slowing down on the way down), the normal force is greater than the weight; this is called overweight. When the acceleration points downward (slowing down on the way up or speeding up on the way down), the normal force is less than the weight; this is called underweight (apparent weightlessness). The person's actual weight never changes.
Scale reading vs. time
Intervals above the green weight line are overweight; intervals below it are underweight.
Think about it
When the elevator slows down on its way down, is the scale reading greater or less than the person's weight?
Greater. Slowing down while descending means the acceleration points upward, so the person is overweight: N = m(g + a) > mg. Watch how the reading changes during the final "slowing down while descending" stage.
Model assumptionsUp is positive · Person at rest relative to the scale · Round trip 11 s
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.