Video: Watch how to do this demo
Description: This demonstration illustrates the combination of similar springs (same spring constant).
Most students do not predict the right outcomes, as this is counter intuitive for most.
- 2 Sets of weights
- 4 of the same silver springs
- 3 Square rulers
- 3 Long poles
- 3 short rods
- 3 S clamps
- 3 Table clamps
- Setup the rods and clamps as shown in the picture. Make sure top three rods are at the same height.
- Tape a square ruler to each post. Make sure all three rulers are at the same height.
- Attach a spring on the left one, a spring on the middle one, and two springs in series on the right one.
- Use the left spring as a reference point for the unstreched spring.
- Attach a mass to the middle spring (1kg works good). Note how far it is stretched compared to the reference spring.
- Ask students what they think will happen when you attach a mass to the 2 springs in series.
- Attach another equal mass to the 2 springs in series. Note that each strings stretches the same, but combined they stretched twice as much as the middle one.
- Ask students what will happen if attach the same mass to 2 strings in parallel.
- Take the mass off the right spring. Take the bottom spring off and attach it to the top right pole.
- Attach the mass to both strings. Note that each spring stretches half as much as the one in the middle, since each effectively “sees” half the weight.
- When finished, remove the masses from the springs.