munge = M = music

Murphy's Law prov.

The correct, original Murphy's Law reads: "If there are two or more ways to do something, and one of those ways can result in a catastrophe, then someone will do it." This is a principle of defensive design, cited here because it is usually given in mutant forms less descriptive of the challenges of design for lusers. For example, you don't make a two-pin plug symmetrical and then label it `THIS WAY UP'; if it matters which way it is plugged in, then you make the design asymmetrical (see also the anecdote under magic smoke).

Edward A. Murphy, Jr. was one of the engineers on the rocket-sled experiments that were done by the U.S. Air Force in 1949 to test human acceleration tolerances (USAF project MX981). One experiment involved a set of 16 accelerometers mounted to different parts of the subject's body. There were two ways each sensor could be glued to its mount, and somebody methodically installed all 16 the wrong way around. Murphy then made the original form of his pronouncement, which the test subject (Major John Paul Stapp) quoted at a news conference a few days later.

Within months `Murphy's Law' had spread to various technical cultures connected to aerospace engineering. Before too many years had gone by variants had passed into the popular imagination, changing as they went. Most of these are variants on "Anything that can go wrong, will"; this is correctly referred to as Finagle's Law. The memetic drift apparent in these mutants clearly demonstrates Murphy's Law acting on itself!

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.

The classic invocation of Murphy's Law in today's world is that of buttered toast falling and landing butter side down. It turns out that we, as bipeds, are doomed to forever have this happen.

Toast has a tendency to land butter side down because it does not have time to flip over. This spin is from the gravitational torque (twist) placed on the bread as it falls over the edge of a table (at about 1 meter (3 feet) high) cannot bring it to make a complete 360 degree flip. Now, if tables were taller (about 3 meters tall) this wouldn't be as much of a problem because the bread would have time flip before it hit the ground.

Why are tables only 1 meter tall? This has to do with our build as bipeds. It is convenient for us. Other animals can get much taller because they fall over less often. As bipeds we are notoriously unstable compared to, say a horse or elephant or whale. At taller than 3 meters (9 feet) if we fell we would shatter our heads. This is generally considered to be a 'bad' thing.

So because we can't reasonably be much taller than 2 meters (6 feet) before problems start occurring this places a maximum height of a table, and thus the tendency for bread to fall and land butter side down.

There are some ways to correct this.

  • Work from tables about 3 meters tall. This gives bread falling from such a height the time necessary to flip to butter side up. This was confirmed in a series of tests that showed that toast falling from normal tables landed butter side down 62% of the time, while landing from tables 8 feet up only landed butter side down 47% of the time.
  • Always put toast butter side down on the table. This implies a very clean table and non-stick surfaces with regards to butter, peanut butter, and jelly (also vegamite if you are from down under). As any parent knows, such a non-stick surface does not exist with regards to these surfaces.
  • Eat very small squares of toast (about 5cm (2 inches) on a side). When these flip over the side of the table, it takes less torque to get them to spin. There is an optimum sized bread for every height table.
  • Tie the toast butter side up to the back of a cat. The cat will always land on its feet and the butter side will be maintained. Note: this may cause the cat and toast to spin and form a perpetual motion machine.
Likely the most practical method is to minimize the time that gravity has to act and apply torque. To do this one must move the bread away from the edge and let it fall normally. Toast dropped from any height with no spin on it will tend to land in the same orientation that it was dropped from. In the case of a edge of a table this means getting the toast away from the edge by pushing it off the table. For a tray, one would move the tray rapidly down (faster than the toast was falling) and then to the side so the toast does not flip.

Face it, the toast will land butter side down more often than not, and Murphy works with the fundamental nature of our existance.

European Journal of Physics 16 172-176 1995

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