Interactive Physics Lab← Lab Bench

MODULE 07 · LAB 3 / LAB BENCH

k from a spring

Find the spring constant k of a spring two ways: from how far known masses stretch it (Hooke’s law, F = kx), and from how fast it oscillates (T = 2π√(m/k)). Then compare the two.

Practice springs

Your assignment

Find k for 2 springs, each with 5 or more loads, by both methods, and report each k with an uncertainty. Time at least 10 oscillations each time you use the stopwatch. Use g = 9.81 m/s².

Which springs?
  1. Read the pointer with nothing on the spring
  2. Read the pointer for each load (stretch method)
  3. Time the oscillations for each load (stopwatch, motion sensor or both)
  4. Fit both graphs and save each spring’s k

The stand

At rest

Magnified stick at the pointer (numbers in cm)

Each small mark is 1 mm. The stick’s zero is level with the hook. Read where the red pointer is, to the nearest millimetre.

Pull the weight down by hand: press on it, drag it down and let go. Or use the button for a 3-2-1 countdown. The orange counting marker on the rod draws a line across to the stick. Drag it (or Tab to it and use ↑ ↓; Shift moves 1 cm) to a level the mass passes, and count each time it passes going down.

2 · Measure and record

02

Type the mass you hung: you add it up yourself. Use 0 for nothing.

A · Stretch: read the pointer

B · Oscillations: hand stopwatch
0.00s

You do not have to start at the release. Let it swing, then press Start (or Space) as the mass passes the marker or the bottom of a swing: call that “zero”, count the oscillations, and stop as it passes the same point again.

Lab notebook

0 of 2 springs done
A · Pointer readings (a deleted row stays, crossed out)
#Springm (g)reading (m)Delete

No readings yet.

B · Timings (T = t / N)
#SpringMethodm (g)Nt (s)T (s)Delete

No timings yet.

3 · Graphs and fits

03
Timings from

4 · Your results

04

For each spring, work out k from each graph and report it with its uncertainty, to sensible significant figures, then save it. Your graded value is k from the oscillations.

k from oscillations±N/m
k from stretch±N/m