A Normal Force: An Encounter with Turtle on a Chicago Highway
A true story.
“The concrete highway was edged with a mat of tangled, broken, dry grass, and the grass heads were heavy with oat beards to catch on a dog’s coat… all passive, but armed with appliances of activity, still, but each possessed of the anlage of movement.” – John Steinbeck, The Grapes of Wrath
“In [physics], the normal force is the component of a contact force that is perpendicular to the surface that an object contacts… A person standing still on a platform is acted upon by gravity, which would pull them down towards the Earth's core unless there were a countervailing force from the resistance of the platform's molecules, a force which is named the ‘normal force’.” – Wikipedia
She once met a turtle in a plaid suit. Well, met is generous. But they sat together for quite some time, that is, at least 9 stops, from 900 W. Harrison to Jackson and Wabash. She was heading home on the CTA bus, tired with the effort of another day’s plodding, worried about the way her career had stagnated, reliving a professional interaction that had squished her dreams like cement hardening around her already stuck feet. It was one of those deceptively cold sunny days of late spring in Chicago - the trees and flowers blooming but ice still in the air. It was like the world just needed a little shift in the wind and it would all open up and be summer. But for now it was held in place by the ice in the air, as if encircled by some transparent igloo: sunshine visible, but inaccessible, walled off by its frozen glass.
Despite the chill she was a little sweaty under the cocoon of her jacket, wrapped tightly around her neck as she boarded the bus. She’d seen it coming at Morgan Street and had half run, half power walked to beat it to the next stop, all the time trying to not look too conspicuous, too immature, too pressed for time.
She cursed herself that she couldn’t seem to outgrow this awkward run-walk habit, developed over years of perpetual tardiness. Late, she’d run down a hallway until the oppressive feeling of judgmental eyes would slow her to a lilting terrapin walk, which she’d maintain until the pressure of her lateness would again compel her back into a lurching run. This might last till the sticky feeling of sweat and worry if she’d smell would again slow her feet. Back and forth, on and on.
Some things never change, she thought.
Newton’s 1st law of motion, on which all physics rests, states that an object in motion will stay in motion and an object at rest will stay at rest unless acted upon by an outside force. Writing in 1686, Newton changed the world with this simple observation: the natural state of an object is to keep doing what it’s doing. Said again: the universe resists change.
The bus was fairly crowded - she picked her way toward the back, trying to not hit people with her book laden hump of a backpack. There were three empty seats, two in the back row, and one a row from the back. The two back row seats were partially and unwelcomely covered. One contained the closed purse of an exhausted looking girl with tightly pursed lips, and the other the jacket of a multiply pierced person hiding behind their clear plastic encased phone. Not great options. But the third seat, the one a row from the back, also gave her pause: it was next to the turtle. His most prominent feature was he shell: a great plaid coat – tight knit and crisscrossed, an old golden tan, like the faded light of sunset in a once bustling town – and a soft brimmed hat – a black felt fedora straight out of a 1920s speakeasy, worn low, over his eyes. His head was pulled into his shell so that his scarf formed a great dewlap covering most of the rest of what she could see of his dark and wrinkled face.
She grabbed a handrail as the bus started to move, and considered her options. To sit in the back row would definitely create a disturbance. But to sit by the reptile, well, clearly the other passengers had avoided him: he had some of those creature-who-might-stink-sit-at-your-own-risk-if-you-know-anything-about-the-CTA vibes. She could just stand, but it’s quite a few stops, and then she would be in the way. She’d turned so she couldn’t see the turtle anymore, standing, directly next to his seat, but still, clearly standing, long enough that her hesitation, though she looked the other way, was probably obvious.
She started to wonder about what this wisened creature is thinking: is he feeling the bite of yet another human avoiding that seat? Is he trying not to feel the dull cutting sensation of rejection? Or is he thinking the opposite – please don’t sit by me, leave me some space? Or, she wondered, is it just my vanity that makes me think he’s thinking of me at all?
Well, I’m certainly thinking of me, she thought. Is it just my racism, my classism, my stereotypes that keep my standing? I’d like to think not. But I don’t know.
She sat by the turtle.
When any two objects come in contact with each other they experience what physicists call the normal force. The normal force is the most basic force in physics: it’s the force of two objects touching, the force of one surface pushing on another.
The normal force is particularly prevalent as the ground underneath you: it holds you up against gravity, it keeps you from falling. It’s the thing that holds you in place, like a chair enfolding your back or a seatbelt constricting your chest.
Effective, you see, at keeping you in your place, at keeping you from moving. Further examples include the force of a cell wall, a closed door, and a concrete floor or road, holding up whatever is on it: a bus, some shoes, a turtle.
By sat, we should clarify, we mean edged her way in: first just one bun, on half the seat. Not too close. For such a momentous move, nothing happened, the turtle stayed put. She examined him out of the corner of her eye. She could see his worn, but creased pants now, and his old black dress shoes. His clothing looked like it was lifted from another time, or, at least, from a thrift store. While old, there’s care worked into this shell. She wondered about where he’s going. To work? An interview? A friend’s place? A dinner party? We know so little about the lives of other humans. Is he lonely?
The turtle continued to look away from her, toward the bus wall, or clouded window. His head remained tucked low, eyes down. She pondered: where is he coming from? Where has he been? What forces keep him looking away and down, keep him in his shell? She wondered about his shell: is it all the protection he has? Me, she thinks, my whiteness and youth and education and network form a protective platform, a great plastron which keeps me safe, and holds me above ground as I trudge through the world. But what protects his insides? What layers of his shell grew during Jim Crow, it’s “overthrow,” and reincarnation in incarceration – an explosion of prison cells and jail bars that make it statistically more-likely-than-not he’s had to feel their iron grip, criminal or no? What layers continue to grow through scared looks and people unwilling to sit by him, through his experience as a perceived threat?
The normal force derives its name not from normal as “usual” or “commonplace,” but rather from the mathematical usage of normal as perpendicular, or at right angles. Normal originates from the Latin word norma, which refers to a carpenter’s T-square, a rule or standard used to define and create a right angle, to force structures straight. Indeed normal lives at the juncture of two facets, as Jonathan Moorley writes: “On the one hand, normal is describing a fact in the world—a line may be orthogonal, or normal, or it may not. Normal is an objective description of that line. But a right angle, in geometry, is also good, is desirable, is a universal mathematical truth that many mathematicians, then and now, describe as a type of beauty and perfection… Normal is both a fact in the world and a judgment of what is right.”
The bus stoped by Canal and a crowd of people got off. The person sitting in the outside seat of the row in front of them quickly rose and swung into a newly open row to sit by herself. There was now another empty pair of seats a few rows up – should she move? But she remembered what her friend Micah told her the other day about the CTA. He said that he sometimes feels a little bond to the person he’s sitting with, sharing this ride –the sweat, the smells – just millimeters apart, or perhaps even jackets touching. There’s something lovely, he said, of two strangers brought together in a little moment, a little sliver of spacetime, not talking, but together, a shared experience of the world. And so he feels sad when a different seat opens up and your new companion abruptly gets up and moves when a different seat opens: a rejection, a breaking of ties – felt as a loss.
Though they – she and the turtle – were uncomfortably squished together on these hard blue seats, a small wave of thankfulness for the company in this brief passage through the lonely expanse of space and time passed behind her eyes. She stayed where she was.
Wikipedia notes that the “Normal force is …not a true force per se” explaining that it is the result of the trillions of microscopic interactions of electrons at the surfaces of the objects. It continues “two bodies do not penetrate each other due to the stability of matter, which is… a consequence of Pauli exclusion principle, but also of the fundamental forces of nature.”
The stops passed, people cycled on and off the bus. She’d shifted more comfortably into her seat - an inch or two closer to the still creature beside her. But she was not fully settled. Her thoughts were still fixed on the turtle. Does he think I’m afraid of him, that I dislike him? Can he sense my curiosity, my desire to share a word, to connect? Is he like me – wanting a new adventure, but contained in the structures dealt him, held in place by the myriad of invisible forces that anchor our minds?
Her mind wandered to the sermon she’d heard the previous Sunday. They’d had a guest preacher, an older baptist reverend from the west side. His great booming voice described how Jesus’s disciples quaked in a boat that was, as the gospels say “buffeted by the waves because the wind was against it,” and how they cried out as Jesus - their leader and companion, approached them walking on the waves. “It’s a ghost!”
He told of the point when Peter “got down out of the boat, walked on the water and came toward Jesus.” He read “But when Peter saw the wind, he was afraid” – and then stoped. “Who can see the wind?!” the Reverend Jackson asked. “The way I see it, the wind we see is something we make up in our minds.”
He described the narratives we all construct, the stories people tell themselves about what’s going to happen or what this person or that person will think. The invisible stories that keep us, and others in our place, that make us all stop, and sink.
Am I scared of the wind, she wondered, contained by its icy grip?
With even the smallest of inclines the normal force can be deceptive. Since it always acts perpendicular to a surface, if the surface you stand on is even slightly tilted, it is no longer the only force pushing against gravity – the only force that holds you in place. You might not notice. You still are, after all, perpendicular to the ground. But in fact, what feels normal is no longer fully normal. You’re also now, in part, held in place by friction, a contact force along the surfaces of objects, parallel to any surface. Friction, that resistive force that keeps things from sliding. It’s both the normalcy of things and the friction – the way the ramp grates against your feet – that hold you there. It keeps you from falling, yes, but also perhaps, from moving at all.
They were approaching her stop. She considered which was ruder, which showed more respect – to reach across and pull the wire herself, her arm flung across his eyes, or to ask him to pull it, possibly implying some sort of colonial structure from the history whose long fingers held them both. She reached across. Pulled the wire. The turtle remained there, still. Closed. The bus stoped. She stood to get off, but wanted the turtle to know she’d been thinking of him, that she wished him well, that she’d noticed their tiny adventure together. She glanced back. “Have a good day” she said quickly.
What happened next – a wonder. The turtle, surprised, moved. Eyes emerged, then thick lips, and then, amazing, so brief she’s wondered since then if she imagined it, a smile – a face unshadowed, transformed. “You too.”
It was only later she remembered that story she once read - some slow moving passage from a Steinbeck novel. In the story a turtle, attempting to cross a highway is struck by a truck swerving to harm it, and flipped off the road. Though upside down and hurting, the turtle moves its limbs till its legs catch a small rock to push on, and then slowly rights itself. As the turtle flips itself over an unnoticed grass head falls out of its shell, sticking seeds in the ground. As the turtle turns to continue plodding on its way its shell drags over the seeds, unintentionally planting them in the ground. The turtle moves away, “drawing a wavy shallow trench in the dust with its shell.”
Normal forces, while important for stability, also are important as agents of change. Newton’s second law tells us that a new outside force – a push, a touch, perhaps even a kiss – changes an object’s motion: new contact creates change.
Newton’s third law tells us something more. Normal forces, it turns out, are reciprocal. If I exert a force on a turtle, it exerts a force back on me.
Off the bus, she doesn’t look back as it pulls away, but instead walked with purposeful strides toward her transfer to the brown line, the next step in her journey. She heard a rumble, and hustled up the stairs: the next train was arriving, and she wanted to be on it.
Stephen Hawking is considered one of the most brilliant minds of the 20th century, an incredible feat considering his diagnosis of an “early-onset slow-progressing form of motor neurone disease that gradually, over decades, paralysed him.” Wikipedia notes that “After the loss of his speech, he communicated through a speech-generating device initially through use of a handheld switch, and eventually by using a single cheek muscle.”
Part of Hawking’s fame comes from his work on black holes, the most inescapable objects of the universe. Nothing, it was believed, could escape a black hole, no information, no radiation. A black hole traps all light. Among other brilliant ideas, Hawking showed that this is not 100% true. If a tiny particle at the very edge of a black hole interacts with a pair particle, one can actually escape. According to Hawking, slowly, over time, even black holes can’t keep everything in. Thanks to the interaction of paired particles, even black holes can’t trap all the light.
Hawking’s best selling book A Brief History of Time opens with an antidote about a well known scientist lecturing on the earth’s orbit and place in space. The scientist is challenged by a woman who insists the world is a flat plate resting on the back of a giant tortoise. Hawking writes “The scientist gave a superior smile before replying, `What is the tortoise standing on?’ `You’re very clever, young man, very clever,’ said the old lady, `But it’s turtles all the way down!’” To that story Hawking adds this: “Most people would find the picture of our universe as an infinite tower of tortoises rather ridiculous, but why do we think we know better?”