In Hooke's law, the force constant k measures how hard a system is to deform. What are its SI units?
- Joules per meter, written J/m
- Newtons per meter, written N/m
- Newtons per second, written N/s
- Meters per newton, written m/N
Show answer and solution
Correct answer: B. Newtons per meter, written N/m
1. Rearranging F = -k x gives k = F / x, so k carries the units of force divided by the units of length.
2. Force is measured in newtons and displacement in meters, so k is measured in newtons per meter.
3. The units of k are newtons per meter (N/m).
4. Joules per meter would be an energy gradient and meters per newton is the reciprocal of a force constant, so neither fits.
_Source: OpenStax College Physics (CC BY 4.0), Ch 16 "Oscillatory Motion and Waves", section 16.1 Hooke's Law: Stress and Strain Revisited_