Falling Toast

What you need

  • Buttered toast
  • A table and an old newspaper
  • An upstairs window with a clear drop to the ground.

What you do

  1. Drop some buttered toast.
  2. Actually, it's not quite that simple. If you hurl toast in the air, flicking your wrist to make it flip artfully, it'll land butter-side-down precisely half the time. Which doesn't help explain the observed butter/carpet affinity.
  3. To more accurately simulate the breakfast calamity, you need to knock toast off the side of a table. (Put the carpet saving newspaper down under it though.)
  4. Do this a few times to be sure.
  5. Now take the toast to your upstairs window. Open the window, and place the toast on the windowsill. Push the toast off the windowsill, just as you pushed it off the table. Repeat and make a note of how many times it landed butter-side-down.

What's going on?

As the toast first slides and then falls off the table it starts to tip over. The tipping point is when the centre of gravity of the toast first leaves the table - for a perfectly square flat piece of pre-sliced toast this will be bang in the middle.

As the toast tips, one side slips down and the other up - the toast is actually gaining angular momentum as gravity pulls on one side and the table resists on the other. Once free of the table the angular momentum doesn't, and can't, just disappear. Instead the toast continues to spin.

The rate at which the toast spins depends on three things, the initial forces it feels as it leaves the table, how long it takes to go from tipping to free fall, and how the mass of the toast is distributed within the slice. As pieces of toast are pretty much all alike (the same mass and distribution of that mass, and the same friction with a table), the way the toast spins as it falls is the same for all loaves of bread.

Tables are also pretty much the same height. So all slices of toast, spinning at the same rate and falling a similar distance, will rotate the same amount as they fall off an average table, usually somewhere between a quarter of a turn and three quarters of a turn. Anywhere in this region will cause the toast to land buttered side down.

If the table is higher, or you push it from an upstairs window the toast will have more chance to turn. Once in a full fall, air resistance comes into play and the angular momentum from the initial fall can be lost. The toast will land butter-up or butter-down an equal number of times.

Special Safety advice

Make sure there is no one below you on the ground, although probably not fatal it would be unpleasant to be hit by cold, buttered, falling toast.