Why do phones land face down?

Question

Layman here.

I'm not sure if this is the case or not, but my anecdotal evidence is that mobile phones, especially large screen phones, tend to fall face down when you drop them; much to the owner's dismay, this leads to cracked screens.

I'm sure there is a scientific explanation for this, so I'd like to know: Why do mobile phones tend to fall and land face first (if so)?

I have a feeling it's related to the way your toast always falls butter side down, or how the shuttlecock always turns toward the same direction, but I'd like to know the explanation.

It is possible that phones land face up as often as face down, but we remember the face down landings much more easily. — Todd Wilcox, Nov 09 '17 at 01:08
There's actually a cat inside each phone: that's how they work. When you drop the phone, the cat flips to land feet first, which is screen-side down. — CJ Dennis, Nov 09 '17 at 01:53
Apply butter to the back of your phone to counter this effect. — DeepSpace, Nov 09 '17 at 08:29
Now I wonder if a phone could use the accelerometers to detect a fall and the vibration motor to try and rotate to the back... — JPhi1618, Nov 10 '17 at 16:56
How much does the way the phone lands affect the chance of the screen shattering? If it lands face up, there are still going to be shockwaves that can shatter the screen. — Acccumulation, Nov 10 '17 at 18:50
I suspect the reason may be different for shuttlecocks. Mobile phones don't have feathers. — sammy gerbil, Nov 11 '17 at 03:22
Murphy's Law can also state that the probability of getting a cracked screen after an accidental fall is much higher than impacting with its backside specifically designed for absorbing the falls. — Narasimham, Nov 11 '17 at 10:00
For the same reason that toast always lands jelly-side down. — Emilio Pisanty, Nov 11 '17 at 17:03
Related: How do cats flip in mid-air without violating the conservation of angular momentum? — Peter Mortensen, Nov 12 '17 at 01:39
The screen has a large chance of shattering when the phone lands on a corner, due to the stresses induced. And the chances of landing on a corner are much higher than landing flat on the front face. — fishinear, Nov 12 '17 at 14:30
My personal experience - which is supported also by probability theory - that phones land with their corners. — peterh, Nov 12 '17 at 21:58
@Barmar That raises the question, what will happen if you butter a cat! — Jeroen, Nov 13 '17 at 15:53
I had no idea I accidentally conjured a well-explored paradox....... — thanby, Nov 13 '17 at 16:26
In my experience they almost always land on a corner and not face down. — mathreadler, Nov 13 '17 at 18:58
I thought of answering it with my own experience, but not enough rep! I have observed my phones mostly falling on one of the top corners, tilted such that the face (glass surface) hits next and it stabilizes that way. I had reasoned this by my (not so strong?) observation/feeling that it is heavier at the top (half) than the bottom one. I have been assuming the same about comparing front vs back of phone faces (despite battery?). I can be wrong though. But I almost surely don't thinks it's a psychological thing, because I handle my phones with a lot of care & I don't forget even a single fall. — 0xc0de, Nov 23 '17 at 05:01

KutuluMike · Accepted Answer · 2017-11-10T23:08:39.103

227

A physicist working at Motorola actually did this experiment as part of a promotional push for shatter-proof screens. This same physicist had previously written a paper on the same question, applied to the classic "buttered toast" problem (does toast really land butter side down?).

The short answer is: the way the phone lands depends on how it is oriented when it leaves your hand. People tend to hold their phones the same way: face up, at an angle, fingers on either side, slightly below the phone's center of gravity, at just about chest-high. The phone also tends to "fall" the same way: slips out of your hand and you fumble slightly trying to catch it.

Given all those parameters, when the phone drops out of your hand, it typically flips over a half a revolution by the time it contacts ground. If you were holding the phone flat, or upside down, or lower to the ground, the result would be different. But given the relative uniformity of the way people hold the phones, there's a corresponding relative uniformity in the way they land when dropped.

edited Nov 10 '17 at 23:08

answered Nov 08 '17 at 22:29

KutuluMike

1,549

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It'd actually be interesting to investigate this independently of the fall height and path, i.e. depending only on the phone's own shape and mass distribution. – Gallifreyan Nov 08 '17 at 22:31
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@davidbak http://www.academia.edu/6794263/Tumbling_toast_Murphys_Law_and_the_fundamental_constants – Keith McClary Nov 09 '17 at 03:53
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Worth noting that Robert Matthews was actually awarded an Ig Noble Prize for his research: https://www.improbable.com/2012/12/24/tumbling-toast-the-maths/ – pajonk Nov 09 '17 at 06:54
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I have no idea anymore where I read the follow-up research, but I recall this being a universal property. Even on other planets with different gravities, bipedal humanoids would have their hands at heights inversely proportional to the gravity, which kept the average number of rotations at 0,5 independent of gravity. – MSalters Nov 09 '17 at 09:44
@TimE.Lord the fall height is similar for different persons: I don't have stats, but based on experience and a cursory look at these data I'd say that most adults in the world are between 1.6 and 1.9 m high. – DeltaIV Nov 09 '17 at 14:37
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This reminds me an old problem my physics teacher gave us to prepare us to the entrance exams for engineering school. For French readers, it can be found at http://mines-ponts.fr/pages/upload/getFile.php?FID=51 (source page: http://mines-ponts.fr/pages/upload/sujet/sujet.php, 1999, PSI, "Physique 1"). The conclusion is indeed: it's because of the initial conditions of the drop (of a buttered toast, not a phone, it was back in 1999!): mainly the height. As @MSalters also stated, the exercise ends by showing the problem would be the same for Martians. – Evariste Nov 09 '17 at 17:51
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But also keep in mind that Matthews says in the video that there is "a slight tendency" to land screen down, so you shouldn't place too much emphasis on the physics. – WhatRoughBeast Nov 09 '17 at 19:14
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So the moral is ... always hold your phone upside down? – Dawood ibn Kareem Nov 09 '17 at 19:35
@DawoodibnKareem or attach a buttered piece of toast to the back (butter side down) – Martin Beckett Nov 09 '17 at 23:12
Cool! Telecommunications with emergency breakfast for those rushed mornings! – Dawood ibn Kareem Nov 09 '17 at 23:14
Yes, I once wrote up the physics of "buttered toast", for a coworker. – Pieter Geerkens Nov 10 '17 at 01:23
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I want to add that Motorola really knows what their doing. I have one of their phones and I've dropped it on the screens several times and haven't had so much as a scratch on the screen :) – Keith M Nov 10 '17 at 04:02
Maybe just butter the battery side of the phone? – rackandboneman Nov 13 '17 at 19:23

score 34 · Answer 2 · answered Nov 09 '17 at 05:04

34

I think one of the commentators summed is up nicely, that you are more likely to forget the times when it lands face up.

It's a psychological phenomenon that Christopher Chabris and Daniel Simons touch on in their book: "The Invisible Gorilla".

In short, it comes down to the fact that a phone falling face-down tends to be much more traumatic for the owner of said phone, and the mental trauma caused tends to leave a bigger impact on your memory. Whereas a phone landing face-up is quickly forgotten. Thinking back, one is therefore likely to only recall the phone falling face-down.

answered Nov 09 '17 at 05:04

user17781

449

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If you're looking for actual psychological terms to read about, try cognitive bias; in this case confirmation and negativity biases would be a good place to start. – nexus_2006 Nov 10 '17 at 13:04
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“The root of all superstition is that men observe when a thing hits, but not when it misses.” -- Francis Bacon – Nov 10 '17 at 14:05

anna v · Answer 3 · 2017-11-09T07:09:26.463

The answer by @KutuluMike gives a good reason.

Psychology can enter in the way one holds a phone even if not chest high to be given a half rotation. The crux is that the phone always faces out of the palm of the hand. It would be an unusual owner who would have the palm on the screen face, so even from low levels where rotation is not possible the probability of the palm letting go downwards is higher than on edge or back of phone.

Seldom a phone will be ejected from the palm ( falling downstairs?) in a random direction. If the palm faces up, the phone is safe, if down , as it is always held face out hitting with the face down is the most probable outcome.

So ultimately the answer to "why do phones land face down" is "Because they are held in the hand face up."

I would add that in the time available for the falling object to strike the ground, there is insufficient time for aerodynamic effects to affect the orientation of the phone. this is not true for flat objects dropped from a height of, say, 5 to 10 meters. — niels nielsen, Nov 09 '17 at 19:26

Why do phones land face down?

3 Answers3