Sallyportal: Madly Blogging Reed

Cracking Eggs with Physics Majors

By Chris Lydgate ’90 on October 30, 2014 11:58 AM

Physics 101 students investigate conservation of energy by catapulting eggs across the Great Lawn. Photo by Tom Humphrey

Making my way to the library the other day I came upon an intriguing sight: a dozen students in Physics 101 firing eggs across the Great Lawn with a makeshift slingshot.

The students were applying the principle of conservation of energy to a devilish problem—determining the minimum angle of trajectory required to be sure that an egg will actually smash when it hits the ground.

At first glance, the experimental apparatus—some sturdy forearms and a length of surgical tubing—seemed rather primitive. But in physics, as elsewhere, appearances are often deceptive. It turns out that only four measurements are required for this investigation. First, the angle at which the egg is fired into the air. Second, the distance between the launch site and the landing site. Third, the mass of the egg. Fourth, the height of the grass. Armed with these numbers, the students can calculate the force with which the egg strikes the dirt.

The first couple of shots failed to smash the eggs, much to the students’ dismay (recent rains, they theorized, may have softened the ground). On the third try, however—at an angle of 52 degrees and a horizontal displacement of 59 meters—the intrepid egg was finally laid waste, to huzzahs from the assembled onlookers.

Trooping back to the lab, the students embarked on the next stage of the experiment—determining the amount of force necessary to crack an egg by piling iron weights atop an egg nestled in foam padding (a cruel science, physics). Finally, they compared this number with the one derived from Newton’s second law of motion.

Fun? Yes. Frivolous? Definitely not. The experiment demonstrates the conservation of energy, spurs debate on the best way to model collision, and poses questions about structural integrity. Talk to a Reed physics major about this subject for any length of time, and you’re liable to wind up discussing bicycle helmets, cannonfire, and whether the Coriolis Effect played a role in the Battle of the Falkland Islands, a WWI naval engagement when shells fired by the British battlecruiser Inflexible kept landing astern of their German targets.

I have always admired Reed’s approach to physics, delightfully condensed by a recent quote I ran across by Prof. Nicholas Wheeler ’55 [physics 1963-2010]: “My ambition was to get to the bottom of things,” he says. “At the time I still supposed that was possible, but the bottom was far deeper than I imagined.”

Tags: physics, ovoid ammunition, Coriolis Effect,