01The same drop, split ten ways, is a different event
Push a case down 6–14 steps totalling 1.0–2.6 m and you could add the heights and call it one fall of equal energy. The arithmetic is correct and useless. What actually happens is six to fourteen separate contacts, each carrying a fraction of the energy, with tumbling and sideways sliding packed in between. Nothing in that sequence resembles one clean impact.
Low peaks are not gentle. A single landing may reach only a third to a half of the acceleration a big drop produces, yet the edge takes 4–12 hits instead of one, and the material at that spot yields and recovers over and over. Cumulative damage follows count and location, not the tallest spike, so no total height can stand in for this run.
028–45 N·m per step, one load each
Energy per step comes from step height and mass and measures 8–45 N·m in practice. That is modest, roughly a tenth of a 1 m free fall. Modest energy also means the case still has speed when it lands, so it keeps tumbling and the next contact lands nowhere near the last one. Nothing here repeats, or lands the same way twice.
Each step takes its energy out of the case in its own way. An edge lands first, the body pivots around it, then a second edge or a face arrives. Some of that energy turns into rotation instead of deformation, sparing the material at that instant while shifting the impact site for the step below. Damage spreads along the edge rather than stacking in one dent.
034–12 edge contacts, all on the same edge
Over 6–14 steps with 150–200 mm risers the edge is struck 4–12 times. Fewer hits than steps, because some landings are flat; never exactly steps plus one, because pivoting carries contact to a neighbouring edge. That spread is itself evidence that where the case lands is not under anyone's control. The count, not the step height, carries the information.
The location, unlike the timing, is predictable. Edges protrude, so whatever the orientation, an edge meets the step nose first. Run ten steps and dents cluster along that edge, spaced according to step height. Inspection starts at those clusters rather than in the middle of a panel, where almost nothing structural happens at all in a run like this.
040.5–3 s per step, and scuffing needs sideways travel
A case does not leave a step immediately. It rests there for 0.5–3 s, sliding, rebounding, drifting sideways. Scuffing is made in that window: normal load supplies friction, lateral travel scrapes material away. No dwell and no travel means no scuff, which is why a fast clean tumble leaves less marking than a slow one. Dwell time decides how much material leaves.
Visible accumulation of 0.2–1.5 mm is the easy number to log and the less important one. Under a deep scuff the wall is thinner, so the next hit at that spot meets lower local stiffness and the dent grows faster. Depth means little without position, and position means little without the step number. Log both fields, or the number is useless.
05Stop every 2–4 steps, measure, continue
Checks sit at 2–4 step intervals. Inspect only after the full run and the scuffs blur into each other; stop every few steps and each increment can be tied to a step number. The stop follows a script: edge scuff depth, latch condition, which face the case came to rest on. All three values go on one sheet.
Two tables decide it. One pairs step number with scuff depth, the other pairs step number with latch state. A sudden jump in depth after a particular step says landings concentrated on the edge there; latches loosening at that step say the pivot direction changed. If the two tables disagree, the run is void and both tables get rewritten.
| Step height | 150–200 mm |
|---|---|
| Step count | 6–14 |
| Energy per step | 8–45 N·m |
| Total drop | 1.0–2.6 m |
| Edge contacts | 4–12 |
| Dwell per step | 0.5–3 s |
| Accumulated scuff depth | 0.2–1.5 mm |
| Check interval | every 2–4 steps |
FAQ
Why not treat the total drop as one fall?
A total gives one energy sum; a staircase gives six to fourteen separate loads. Low peaks, many hits and a concentrated location decide the damage pattern, and a single fall cannot reproduce that combination in any useful way.
Is 8–45 N·m per step a lot or a little?
About an order of magnitude below one 1 m free fall. The size is not the point. Repetition is: the same edge takes 4–12 hits at that level, and accumulation at one spot outruns any single bigger impact.
How deep can scuffing get before I stop?
Watch the increment, not the absolute depth. A clear rise between two consecutive checks, or a scuff base gone pale and fibrous, means stop and inspect locally instead of finishing the remaining steps.
The clip shows the edge being hit. Why keep a record?
The clip documents the run; the verdict comes from step number paired with scuff depth. Footage is not a load-bearing or protection rating, and release depends on logged depth, count and check interval.
