As a physicist, it seems obvious to me that the fundamental laws of nature are an important foundation to any technological society.
Sometimes I worry that connection may not be so clear to my students.
This year I asked my Elementary Physics students to imagine a future civilization, either humans who have survived some terrible apocalypse or some newly evolved species following in our footsteps in need of our assistance. What missive would my students leave to help them rebuild their knowledge of how the universe works?
I expected some to follow the example of the physicist Richard Feynman, whose own answer was a terse “stuff is made of atoms.” Thanks to the Greeks, we had that worked out thousands of years ago, so I secretly hoped my students would be a bit more clever.
And they didn’t disappoint me.
Some focused on the broad outlines of the scientific method and the need to always ask questions as the hallmark of a technological society. But when they got down to the details, nearly all of them chose to recap Isaac Newton’s Laws of Motion.
This could be because slightly more than four chapters of their text are devoted to these laws, or, befitting the season, that Isaac Newton was born on Christmas Day in 1642. Whatever the reason, considering how long it took us as a species to work them out, I think my students were on the right track.
Newton’s first law states that any object will maintain its motion, or stay at rest, unless acted on by some other force. This law codified the notion of inertia, the property of matter that tends to resist changes in motion. It also provided a connection, for the very first time, between the motion of planets around the sun and the movement of common objects around us. This, along with earlier observations of sun spots and lunar craters, brought “the heavens” squarely into our earthly realm.
Newton’s second law described the relationship between the force on an object and how much it accelerates, with a larger force resulting in a larger change in speed. Newton also found that more massive objects required a larger force to get the same acceleration. This mathematical description defined mass for the first time in terms of the observable properties of motion.
From these two laws, Newton realized that any object at rest must have zero net force acting on it. So, an object resting on a table, something that would otherwise fall to earth if left to its own devices, also experiences an upward force provided by the surface that keeps the downward force in check. Thus, Newton’s third law determined that every force must be paired with an equal and opposite force, something you’ve learned if you’ve ever bumped into anything solid.
This pondering of why an object would fall to Earth in the first place led Newton to his law of gravity. As the story goes, Newton was thinking about the motion of the moon when he was hit on the head by a falling apple. He realized in that moment that his three laws would explain the motion of both the Moon and the apple. The only difference is the apple hits the ground before getting a chance to complete its orbit.
While the story is likely apocryphal, the similarity of motion between the two objects is not. Gravity pulls the apple (and the Moon) towards Earth, but the speed of the Moon’s orbit keeps it from intersecting Earth’s round surface.
This notion of gravity was a struggle even for Newton. All the other forces he considered involved a direct push or pull, but gravity provided its force with no visible means to convey it. And yet, Newton’s formulation of gravity described well the observed motion of the planets. In a fit of pragmatism befitting one of the world’s first physicists, he noted that gravity must be caused by something, “but whether this agent be material or immaterial, I have left open to the consideration of my readers.’’
A brief time later, it was the French mathematician and physicist Émilie du Châtelet who translated and provided commentary on Newton’s often cryptic writing. She was responsible for popularizing and expanding upon these concepts, thus leaving her own message for future generations. If it wasn’t for her, maybe it wouldn’t have caught on as quickly as it did.
Going to show that, like my students’ efforts, often it’s the communication and reinterpretation of these ideas that is the real foundation of physics.