The Physics of Bicycles
The Physics of Bicycles — an illustrated science story. 10 illustrated pages, free to read on Wonder Science.
Page 1
Floating high above the city of San Francisco, the Sky Market buzzed with activity. Merchants traded in bottled weather, from gentle fog to full-blown thunderstorms. Among them, Omar watched a delivery drone carrying a peculiar package: a bicycle, wobbling precariously. The physics of bicycles might seem simple, but staying upright involves complex forces and motion. In fact, bicycles are so efficient that a cyclist uses about 50 calories to travel one mile, compared to about 100 calories walking the same distance!
Fact: The bottled weather is inspired by real experiments in cloud seeding and weather modification.
Page 2
Omar frowned. 'That bike looks like it's about to fall!' she exclaimed. Anders, an elderly woman in her 60s, petite but confident, with light brown skin with warm undertones and buzz-cut dark brown hair with defined eyebrows, working at a weather stall nearby, chuckled. 'It needs a rider, dear. A bicycle isn't stable on its own. You need to set it in motion. That forward motion creates what's called angular momentum.'
"'That bike looks like it's about to fall!'"
Fact: Angular momentum is a measure of an object's rotation, and it keeps the bicycle upright when moving.
Page 3
Omar tapped her notebook. 'Angular momentum... is that like a spinning top?' Anders nodded. 'Exactly! The wheels act like gyroscopes, resisting changes in their orientation. This gives the bike stability.' Omar remembered something she'd read. 'Didn't someone say, "The important thing is not to stop questioning?" I think it was Albert Einstein who said that.'
"'Angular momentum... is that like a spinning top?'"
Fact: Gyroscopic effect is one factor in bicycle stability, though other forces also play a role.
Page 4
Anders explained, 'Another key is steering. When a bike starts to lean, you naturally steer into the fall. This moves the wheels under your center of gravity, keeping you balanced.' She grabbed a model bicycle. 'Think of it this way: to stay balanced, you must constantly adjust the contact patch between the tire and the ground so it remains directly beneath your combined center of mass with the bike.'
"'Think of it this way: to stay balanced, you must constantly adjust the contact patch between the tire and the ground so it remains directly beneath your combined center of mass with the bike.'"
Fact: Steering counteracts the lean, bringing the bicycle back to an upright position.
Page 5
To illustrate, Anders brought out a small scale and a weighted doll. 'See, if the doll's center of mass is directly above the base, it balances. If it shifts, it falls.' Anders explained. 'On a bike, your body and the bike become one system. You shift your weight to keep that center of mass balanced over the wheels.'
"'See, if the doll's center of mass is directly above the base, it balances. If it shifts, it falls.'"
Fact: The combined center of mass of the rider and the bicycle must stay over the wheels for balance.
Page 6
Petra, a woman in her mid-40s female, short and energetic, with rich dark brown skin and sleek straight dark brown hair in a low braid, appeared. 'Don't forget the trail!' she called, joining the conversation. 'The trail is the distance between where the front wheel touches the ground, and where the steering axis intersects the ground. This helps the bicycle self-correct and stay stable, but it can only work when the bicycle is moving.'
"'Don't forget the trail! This helps the bicycle self-correct and stay stable, but it can only work when the bicycle is moving.'"
Fact: Trail is a design feature that contributes to self-stability in bicycles.
Page 7
Omar scribbled furiously. 'So, it's a combination of forward motion, steering, center of mass, and geometry that keeps a bike upright?' Petra smiled. 'Exactly! Engineers consider all these factors when designing a bicycle.' 'That's how the bones cycle was able to work so well!'
"'So, it's a combination of forward motion, steering, center of mass, and geometry that keeps a bike upright?'"
Fact: Engineers optimize bicycle design to balance stability and maneuverability.
Page 8
Suddenly, a strong gust of bottled wind escaped from a broken container nearby, sending the delivery drone spinning wildly. The bicycle slipped from its grasp, hurtling towards the edge of the Sky Market! 'Oh no!' Omar cried. 'That bike's going to fall into the bay!'
"'Oh no! That bike's going to fall into the bay!'"
Fact: A sudden force can disrupt the equilibrium of a moving bicycle.
Page 9
Thinking fast, Omar grabbed a nearby weather bottle filled with gentle fog. 'If I can reduce the wind resistance...' she muttered, uncorking the bottle and releasing the fog. The fog swirled around the falling bicycle, slowing its descent just enough. Petra used a mechanical arm to grab the bike, preventing a crash.
"'If I can reduce the wind resistance...'"
Fact: Reducing wind resistance can slow down a falling object, as demonstrated by Galileo.
Page 10
With the bicycle safely secured, Omar smiled. 'Understanding the physics of balance helped save the day!' she exclaimed. Anders nodded wisely. 'Indeed. And remember, like a bicycle, life is about balance. You have to keep moving forward to stay upright!' It's not just about gears and pedals; it's about understanding the world and the small moments that make every day an adventure.
"'Understanding the physics of balance helped save the day!'"
Fact: Understanding physics can help solve real-world problems and make a positive impact.
About this story
- Audience: kids (ages 6–12)
Questions and answers
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