Toast landing butter-side down

Settled in 1995 by Robert A.J. Matthews.

The folk belief that dropped buttered toast is unusually likely to land butter-side down is often filed under Murphy's Law folklore, and was long dismissed by scientists as a psychological illusion. In 1995 physicist Robert Matthews used rotational dynamics to show the belief has a real physical basis: toast tipped off a table typically only has time to complete about half a rotation before hitting the floor, given ordinary table heights and human dimensions, biasing it toward landing butter-side down. Matthews further noted, somewhat tongue-in-cheek, that this traces back to the values of fundamental physical constants that set human and table scale - work that earned him the 1996 Ig Nobel Prize in physics.

An annoying kitchen mishap turns out to be a genuine, provable consequence of ordinary table heights and the fixed rate at which a flipping piece of toast can rotate before gravity wins.

Explanations that circulated

• A common assumption is that landing orientation is purely 50/50 chance with no physical bias, or that people simply misremember only the annoying outcome; Matthews showed there is a genuine, non-superstitious mechanical bias favoring butter-side-down landings for toast falling from typical table heights.
• Some attribute the effect entirely to the added mass/friction of butter changing aerodynamics; Matthews's analysis instead shows the dominant factor is that a typical table height only allows about half a rotation before hitting the floor, not enough time for a full flip back to butter-side-up.

References

• Tumbling toast, Murphy's Law and the fundamental constants, Robert A. J. Matthews, European Journal of Physics, 1995