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Butter Side Up

A toast to Murphy’s Law! It’s not just bad luck that lands your toast butter-side down—it’s physics!

There are two factors to consider when looking at the “butter side down” phenomenon:

Factor 1: Probability

Does a piece of buttered toast have the tendency to fall on the dry side or the buttered side? It’s simply a more delicious way of asking “heads or tails?” Just like a coin, buttered toast does not have a tendency to fall one way or the other. In a controlled testing environment, the distribution of butter-side-up to butter-side-down over time should be an even 50/50 split. But, there are lots of variables that can affect these results—and that is where the physics of falling toast becomes very important.

Factor 2: Physics

Thanks to physics, a piece of falling toast encounters many variables on its way to the floor. Here are just a few things to watch for next time your toast decides to jump:

  • Period of Rotation: If you were to drop a piece of toast from your kitchen table, it will rotate as it falls. The period of rotation is the time it takes for the toast to complete a full 360 degree spin. The problem is that the floor interrupts the fall right in the middle of the toast’s rotation—this will cause the toast to go from butter-side-up to butter-side-down. The higher the point at which the toast is dropped, the greater the chance for it to complete a rotation—and land butter-side-up. Though we can’t recommend standing on your breakfast table, it’s a practice that could greatly improve your chances of salvaging your dropped toast.
  • Moment of Inertia: At the moment a piece of toast begins flipping towards the kitchen floor, it has inertia—it doesn’t want to stop flipping if it doesn’t have to. Its moment of inertia is determined by the speed at which the toast is flipping, combined with the size and mass of the toast. Most breakfast toast is about the same size and mass, unless you’re in Texas—home of the giant slices that carry the state name. But any way you slice it, the same rules apply. Add a little velocity to the spin as your breakfast goes sliding off your plate—give it a smack to add some inertia and see how it lands.
  • Angular Momentum: Just like a frisbee or a gyroscope, your toast gains stability when it spins. In fact, the faster it spins, the more stable it gets. This is angular momentum, or mass in motion around a single point, in action. Newton once claimed that a mass in motion likes to stay that way, and this is definitely true for toast. Once your toast is spinning, it wants to keep spinning—that is, until some other force acts on it…like the floor.

 

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