Apparent weight is the normal force
- 01
The tempting model
Treating scale reading and gravitational weight as always identical.
- 02
Why it feels right
A bathroom scale is used as a weight meter, so its reading feels like mg.
- 03
Where it breaks · how to catch it
You answer mg for a scale in an accelerating elevator without applying Newton's second law.
- 04
The correct model
A scale reads the normal force. In an elevator accelerating upward, N - mg = ma, so N = m(g + a); accelerating downward gives N = m(g - a).
- 05
Repair · see it, then test it
worked example A 60 kg student stands on a scale in an elevator accelerating upward at 2 m/s². What does the scale read?
Tempting move
mg = 588 N.
Correct move
N = m(g+a) = 60(11.8) = 708 N.
Test the repair NL-14 · transferinclude NMake a fresh prediction before referring to the worked example.
Then practise it on the ladder
R11Apparent weight in an elevatoradds: A scale reads normal force, not gravitational weight.