The Great Pumpkin Drop

“I once observed some of your classes in our Peer Evaluation System. There, I learned that I would have loved to be a science teacher.”

J.P. (French and History teacher at my school, retired)

My response: 

Out of all the subjects, we (science teachers) do have the best toys. Kids don’t seem engaged? Just blow something up or light your hand on fire!

JP: Drop something from the bell tower! Pumpkins! Drop lots and lots of pumpkins!

DD: I loved that tradition!

More on dropping pumpkins: 

Every Halloween, the other physics teachers and I held “The Great Pumpkin Drop”. The entire student body gathered on the front lawn as we dropped a variety of gourds from the Main Building’s bell tower. The event demonstrates that no matter the fruit, it takes 2.27 seconds for it to hit the ground below. That translates to them falling 25.3 meters (83 feet!). They hit the ground at a speed of 29.7 m/s (64.3 mph). Most importantly, the splat factor was incredible!

The activity is meant to reflect the story of Galileo dropping different sized cannonballs from the Tower of Pisa. His exercise showed that, barring the presence of an additional force such as air resistance, everything should accelerate at the same rate in a given gravitational field (9.8 m/s/s or 32 ft/s/s). 

The pumpkin drop delivers a real-world demonstration of an abstract concept. No matter how many times the students run the numbers in a lab or on a piece of paper, it is still a shock for them to see it in action. And not just them — no matter how many times I’ve dropped pumpkins from a bell tower, it still amazes me!

Galileo’s experiment is traditionally considered the dawn of modern science (even though there is no written record of him actually having done this demonstration when in Pisa). It is hailed as the first time that scientific ideas were tested in ways that were more than anecdotal, and it ushered in an era when curious people began testing hypotheses in more rigorous, systematic and mathematical ways. If their results matched the original ideas, the ideas could be considered valid. This aggressive questioning of ideas and experience is the essence of the scientific method, the true expression of the notion that seeing is believing. 

The fact that everything falls at the same rate when in a given gravitational field is another example of a discrepant event. We “see” heavier things fall faster than light things. A book hits the ground before a single piece of paper. Dust floats in the air while raindrops fall more quickly. An adult sledding down a hill is usually going much faster than a child. Anecdotally, it seems that heavier stuff falling faster is obvious.

But why is it that the more people that get on a roller coaster doesn’t make it go any faster than if the ride carried fewer passengers? What would happen if you dropped a book with one sheet of paper on top of it? Do all rain drops fall at the same rate? Even these few examples show that there is a lot more going on when things fall than we know. That thing that makes this so messy is air resistance. When an object moves through the air it has to push the air out of the way. And, the air pushes back. 

Aristotle argued that heavier objects fall faster than lighter ones because of their natural motions. Rock (Earth) and Water naturally go down while Air and Fire have the tendencies to go up. Since a large boulder has more Earth in it than a pebble, it should go down more quickly. Galileo famously argued that if a heavy stone fell faster than a lighter one, tying them together would create a contradiction—the lighter stone would slow the heavier one, yet together they would form a heavier object that should fall faster. In reality, they fall at the same rate once the effects of air resistance are removed.

The Pumpkin Drop is a real-world demonstration of the constant acceleration of objects in a gravitational field. But if you are a fifteen-year-old high school student, what you really remember is the remarkable, ultra-satisfying rush you get when you see things smash epically from 85 feet up! It’s easier to remember a lesson when part of it entails dodging pieces of smashed pumpkin. 

For teachers, the rush continues after the splat. The students record the event. We can use the video to get the data that proves Galileo right. And every year there are always a few students who want to see how gravity works on other objects moving in other directions. What happens if you flick two quarters off the edge of a table…or a quarter and a nickel…or a quarter and a Twinkie…? They seek out confirmation on their own!!

I’m a fan of all forms of learning. Languages give voice to thought. The arts let students express themselves through images, sound, and movement. The humanities help us look inward and outward to better understand ourselves, others, and other cultures. But the sciences let teachers operate at the intersection of highbrow and lowbrow. Our students study mathematical descriptions of the fundamental forces of the universe. And sometimes they do it by dropping large fruits from a tall building and watching them explode on impact. We really do have the best toys!