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A bit about bikes

Heymatt:

Why is it that I can balance myself on a bicycle when it's moving, but I can't when it's stopped. When you think about it, that doesn't make sense. Or does it?

-- Bikeman, Bay Park

Depends on who's doing the thinking, apparently. The answer used to be simple but for some reason, that wasn't good enough. You should have asked this a couple of years ago, before some big thinkers got ahold of it. The elves won't give up their training wheels, and they don't care what the answer is, so I'm on my own here.

I assume there's no mystery about why a stationary bike is so unstable. Same reason two-legged bar stools never caught on. You're trying to balance yourself along a line that runs from the contact point of the front wheel to the contact point of the back wheel. You're perpetually a victim to gravity. If somehow you do manage to find the precise point of balance, all you have to do is switch your bubblegum to your left cheek, and you fall to the left. But when the bike's wheels are spinning, the physics of the situation changes. The front wheel acts like a gyroscope, and one thing a spinning gyroscope wants to do is remain stable. Now if you promise to go along with me on this explanation, I promise I won't go into the bloody details of angular momentum. Nobody wants to hear that, believe me.

So this time the bike is moving when you shift your gum (and the center of gravity of you and your gum and the bike). In response, the bike tilts slightly to the left. But instead of caving to gravity, the stabilizing influence of the gyroscopic front wheel (the steering wheel) causes it to turn automatically to the left, under the moving center of gravity. It's the effects of the angular momentum of the wheel and the pressure of the ground against the wheel that cause the shift. The faster you're moving, the more stable this system is. The design of the bike frame and the wheel fork also influence stability. The fork creates a steering axis, and when the moving bike tilts to the right or left off this axis, the wheel automatically tries to correct itself by turning into the direction of the tilt. You can see this even when the bike is stationary; tip it to one side, and the front wheel will pivot to that side. All in all, riding a bike is sometimes described as a whole series of these tiny automatic corrections being made continuously as you pedal along. Personally, just thinking about all this is plenty exhausting, and I'm going to take a nap.

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Heymatt:

Why is it that I can balance myself on a bicycle when it's moving, but I can't when it's stopped. When you think about it, that doesn't make sense. Or does it?

-- Bikeman, Bay Park

Depends on who's doing the thinking, apparently. The answer used to be simple but for some reason, that wasn't good enough. You should have asked this a couple of years ago, before some big thinkers got ahold of it. The elves won't give up their training wheels, and they don't care what the answer is, so I'm on my own here.

I assume there's no mystery about why a stationary bike is so unstable. Same reason two-legged bar stools never caught on. You're trying to balance yourself along a line that runs from the contact point of the front wheel to the contact point of the back wheel. You're perpetually a victim to gravity. If somehow you do manage to find the precise point of balance, all you have to do is switch your bubblegum to your left cheek, and you fall to the left. But when the bike's wheels are spinning, the physics of the situation changes. The front wheel acts like a gyroscope, and one thing a spinning gyroscope wants to do is remain stable. Now if you promise to go along with me on this explanation, I promise I won't go into the bloody details of angular momentum. Nobody wants to hear that, believe me.

So this time the bike is moving when you shift your gum (and the center of gravity of you and your gum and the bike). In response, the bike tilts slightly to the left. But instead of caving to gravity, the stabilizing influence of the gyroscopic front wheel (the steering wheel) causes it to turn automatically to the left, under the moving center of gravity. It's the effects of the angular momentum of the wheel and the pressure of the ground against the wheel that cause the shift. The faster you're moving, the more stable this system is. The design of the bike frame and the wheel fork also influence stability. The fork creates a steering axis, and when the moving bike tilts to the right or left off this axis, the wheel automatically tries to correct itself by turning into the direction of the tilt. You can see this even when the bike is stationary; tip it to one side, and the front wheel will pivot to that side. All in all, riding a bike is sometimes described as a whole series of these tiny automatic corrections being made continuously as you pedal along. Personally, just thinking about all this is plenty exhausting, and I'm going to take a nap.

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4S Ranch Allied Gardens Alpine Baja Balboa Park Bankers Hill Barrio Logan Bay Ho Bay Park Black Mountain Ranch Blossom Valley Bonita Bonsall Borrego Springs Boulevard Campo Cardiff-by-the-Sea Carlsbad Carmel Mountain Carmel Valley Chollas View Chula Vista City College City Heights Clairemont College Area Coronado CSU San Marcos Cuyamaca College Del Cerro Del Mar Descanso Downtown San Diego Eastlake East Village El Cajon Emerald Hills Encanto Encinitas Escondido Fallbrook Fletcher Hills Golden Hill Grant Hill Grantville Grossmont College Guatay Harbor Island Hillcrest Imperial Beach Imperial Valley Jacumba Jamacha-Lomita Jamul Julian Kearny Mesa Kensington La Jolla Lakeside La Mesa Lemon Grove Leucadia Liberty Station Lincoln Acres Lincoln Park Linda Vista Little Italy Logan Heights Mesa College Midway District MiraCosta College Miramar Miramar College Mira Mesa Mission Beach Mission Hills Mission Valley Mountain View Mount Hope Mount Laguna National City Nestor Normal Heights North Park Oak Park Ocean Beach Oceanside Old Town Otay Mesa Pacific Beach Pala Palomar College Palomar Mountain Paradise Hills Pauma Valley Pine Valley Point Loma Point Loma Nazarene Potrero Poway Rainbow Ramona Rancho Bernardo Rancho Penasquitos Rancho San Diego Rancho Santa Fe Rolando San Carlos San Marcos San Onofre Santa Ysabel Santee San Ysidro Scripps Ranch SDSU Serra Mesa Shelltown Shelter Island Sherman Heights Skyline Solana Beach Sorrento Valley Southcrest South Park Southwestern College Spring Valley Stockton Talmadge Temecula Tierrasanta Tijuana UCSD University City University Heights USD Valencia Park Valley Center Vista Warner Springs
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