Falling Buttered Toast
As I was buttering toast on a beautiful Sunday morning, one piece slid off the table and tumbled down. It smacked buttered-side down on the carpet. “Bad luck” flashed through my head—but was it a matter of chance, or was the toast doomed to reach the ground buttered-side down? Time for science to tell us! Take a slice, try it out and learn about the science behind a falling slice of toast!
Objects close to Earth fall because our planet, a very heavy object, pulls on them. The effect of this pull is very familiar but still, our intuition about how fast items fall can let us down. Intuitively, one would think that heavier objects fall faster, but if you take two balls of the same size—a light one and a heavy one—and release them from the same height, both will reach the ground at the same time. This shows how near Earth, the rate at which objects fall straight down does not depend on their mass. This observation was made by Galileo Galilei in the 16th century, and it still surprises a lot of people.
In addition to this, some objects tumble down because one side of the object starts falling before the other. How fast an object rotates while it falls depends on how its mass is distributed with respect to the axis of rotation.
In this activity, you will study how a slice of toast falls or tumbles down, and how the laws of physics and not luck determine which side faces down when your toast reaches the ground.
- Old newspaper or other paper to protect the floor
- A few slices of toasted sandwich bread
- Butter, peanut butter, or any other kind of sticky spread
- Butter knife
- A table 75 centimeters high
- Protect the floor around the edge of the table with an old newspaper.
- Spread a few slices of toasted bread—or toast—on one side with a sticky spread like butter or peanut butter. Spread a few slices thin and a few thick, but always distribute the spread evenly over the bread.
- As a general rule, perform all tests over the protected area on the floor. It will facilitate cleanup after you have finished the experiment.
- Hold a slice buttered-side up with your two hands (one on each side of the slice), parallel to the ground, at the height of the table, and release. Watch as it falls. Which side faces down when the toast reaches the ground?
- Pick up the slice and place it near the edge of the table, again with the buttered side up. Slide the slice over the edge of the table with moderate speed: not too fast, not too slow. Observe as it falls. Did it fall in the same way as the first experiment, or was it different?
- As the slice lies on the ground, observe which side is down this time. Is it similar or different from your first experiment?
- Do you think the outcome of the first test (releasing it with two hands) was the result of a random process (sometimes this side faces down, and other times the other one faces down), or would one side of your slice preferably end facing down?
- What about the second test (sliding it of the table)? Would the side facing down be arbitrarily determined, or would one side be preferred? Why do you think this is the case?
- Repeat both tests with the same or a different buttered slice. Which side hit the ground this time?
- Even if you obtained the same results, this could easily be due to luck. Repeat at least 10 more times. Do you get the same side facing down repeatedly, or does it look like a random toss: sometimes the buttery side faces up, and sometimes it faces down?
- If one side is more likely to land face down, why would that be? Would the heavier (buttered) side predominantly land up or down? What happens when the buttered side faces down when you release the slice or slide the slice off? Perform a new set of tests to find out!
Extra: What would happen if the height over which the slice falls is larger or shorter? Perform another set of tests to find out! Use considerably different heights, like a small chair, a window sill or a balcony. How does it land now?
Extra: Can you design a test to see if the mass of the slice of toasted bread makes a difference? Would a heavy hardcover book fall and tumble in the same way? Predict the outcome and test it out!
Extra: Can you design a test to see if the distribution of the mass of the slice of buttered bread makes a difference? Would a slice with most of its mass near the center fall and tumble in the same way as a slice with the same mass where the mass is mainly located at the edges of the slice? Predict the outcome and test it out!
Observations and Results
Did the slice fall straight down, landing buttered-side up after being released with two hands? On the other hand, did your slice always tumble down and land buttered-side down after sliding off the table?
This is to be expected.
When released with two hands from a horizontal position, all parts of the slice start falling at the same instance. Thus, the slice falls straight down. The pull of the earth determines how fast the slice falls, but at any instance, each part of the slice falls with same speed and the slice lands with the same face up as it was released.
When you slide a slice off the table, one side tips over the edge of the table, causing the slice to rotate while it falls. The pull of the earth still determines how fast the center of the slice falls, but now, the slice also rotates around an axis through this center. How many times the slice can rotate during its fall will depend on the duration of the fall, which is determined by the height of the table. How fast your object rotates is another factor, which is determined by the distribution of the mass of the rotating object. With a table 75 centimeters high, the side of your uniformly buttered toast that was initially facing up will generally land facing down.
The results will depend on the height of the table. When sliding off a low table, the fall takes less time and thus, the slice will rotate during a shorter time. On the contrary, it has more time to rotate when falling off a higher table.
Ask an Expert
- Dispose of your protective paper and throw the sandwiches in the compost bin.
- Showing Science: Watch Objects in Free Fall, from Scientific American