Number of coils held

Observations

Slinky drop length

drop 1

larger version of drop 1

drop 2

larger version of drop 2 

When the slinky has collapsed nearly halfway, a bright line seems to appear just below the top end of the slinky. It can be seen well exactly halfway through both clips. What appears to be a bright line could be a longitudinal wave forming in the slinky, similar to the more dramatic waves that appear when increasing numbers of coils are held.

drop 1

larger version of drop 1

drop 2

larger version of drop 2

As the slinky collapses, the top collapses at a faster rate than the bottom. This faster rate of collapse seems to lead to the gradual appearance of a longitudinal wave, showing up distinctly as a bright line near the middle of the collapsing slinky and at the middle of the clip. In both clips, the top is shown to eventually overtake this wave just before it collides with the bottom. This collision appears to have no effect on the motion of the bottom; the bottom does not move until the top reaches it.

drop 1

larger version of drop 1

drop 2

larger version of drop 2

Unlike the previous case, the wave forms much lower in the collapsing slinky. Before, the wave became distinct (a bright line can be clearly seen) roughly halfway up from the bottom of the slinky. Now, the wave becomes distinct about one-third of the way up from the bottom.

In drop 1, the top, bottom, and wave appear to collide simultaneously, and during this collision, the bottom remains motionless.

In drop 2, the wave and bottom appear to collide somewhat before the top collides with the wave, so that the bottom moves slightly.

The main observation resulting from this is when approximately 30 of the 90 coils are held, the wave begins to reach the bottom before the top can overtake the wave. This causes the bottom to move.

drop 1

larger version of drop 1

drop 2

Almost halfway through the clips, the wave collides with the bottom, and after this point, both the wave and the bottom appear to fall as a unit. The top falls faster than this unit, and soon collides with it. This motion can best be seen in drop 1.

drop 1

larger version of drop 1

drop 2

drop 3 (a bit of glare is present on the slinky during the drop)

The wave forms much earlier in both clips, perhaps due to the shorter length of the slinky, and becomes distinct about one-fourth of the way up, measured from the bottom of the slinky. The wave collides with the bottom, and both fall together. Unlike the previous case, the top takes longer to collide with the wave-bottom unit. Finally, the slinky becomes fully contracted; all parts now appear to fall at the same rate.

Compare with vertical contracted, nonsupported drops of plastic slinky, where slinky falls while fully contracted.

drop 1

drop 2

As the drop length becomes smaller, it becomes more difficult to resolve the top, bottom, and the wave as it gradually forms. However, the collision of the wave and bottom can still be seen, and it appears to take more time for the top to collide with the wave-bottom combination than in the previous case. When the top finally collides with the bottom, the entire slinky becomes fully contracted, and as in the 50-coil case, all parts appear to fall at the same rate.

drop 1

Only one clip each for the 70, 80, and 90-coil drops were taken, since it becomes progressively difficult to resolve different parts of the slinky. Here, the wave forms, and almost immediately, it collides with the bottom. The top, falling faster than the lower portion of the slinky, runs into it. The slinky becomes fully contracted, and still, all parts appear to be falling at the same rate.

drop 1

If any wave formed in the slinky shortly after release, it quickly disappears from view. If there is any separation of the slinky after collapse, suggesting that not all parts are falling at the same rate, it cannot be seen. The slinky continues to fall uniformly.

drop 1

This is equivalent to the vertical contracted, nonsupported plastic slinky drop. Both were dropped in the same way (two fingers support the bottom of the slinky before release). However, the metal slinky is not seen to relax after reaching contracted length as the plastic slinky appears to. A possible reason is that the metal slinky has not fallen long enough for relaxing to appear.