Engineering
Two springs, two ways
You have two identical springs, each with stiffness k. How stiff is the pair when hung one below the other, and when hung side by side sharing a load?
- Hint 1In series, what force does each spring feel, and how do the extensions add?
- Hint 2Side by side, how do the springs share the force, and how do their extensions compare?
- In series, each spring carries the full load F, so each stretches F/k.
- Total extension 2F/k, so the pair's stiffness is F ÷ (2F/k) = k/2.
- Side by side, both stretch by the same x and each pulls with kx.
- Total force 2kx for extension x, so the stiffness is 2k.
- Series springs act like a softer spring; parallel springs like a stiffer one.
Where it lands: k/2 in series, 2k in parallel.
The trap: Mixing the rules up with resistors: springs in series combine like resistors in parallel.
What a tutor might ask next: If you cut one spring into two halves, how stiff is each half?
Now do one out loud. In the interview you think aloud with a tutor. Try an Engineering problem with hints, follow-ups and Mia's feedback on how you think.