4.1 Bicycles

4.1 Bicycles - Observations about Bicycles Key Concepts:...

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1 Key Concepts: • Unstable Equilibrium • Static and Dynamic Stability • Precession Observations about Bicycles • They are hard to keep upright while stationary • They stay upright easily while moving forward • They require leaning during turns • They can be ridden without hands Question 1 Why is a stationary tricycle so stable? Vehicle’s Static Stability (1) Static stability is determined by 1. Base of support (polygon formed by ground contact points) 2. Center of gravity (effective point at which gravity acts) Static stability occurs when the center of gravity is above the base of support c o m Vehicle’s Static Stability 2 If center of gravity lies above base of support, when tipped: – Gravitational potential energy rises – Acceleration is back toward equilibrium and vehicle or object returns to equilibrium. Vehicle or object is then: “statically stable”, or “in stable equilibrium”. Gravitational potential energy increases mgh mg h Question 2 Why is stationary bicycle so unstable?
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2 Vehicle’s Static Stability (3) If center of gravity does not lie above base of support, when tipped: – Gravitational potential energy decreases – Acceleration is away from equilibrium and vehicle or object does not return to equilibrium, it tips over . Therefore vehicle or object is : “is statically unstable”, or is “in an unstable equilibrium”. Tips over to a new stable equilibrium Energy becomes smaller in this direction mgh Tricycle: statically stable Bicycle: statically unstable You can also understand this using torque Stationary Vehicles: • Tricycles – have 3 contact points – are statically stable and hard to tip over •B
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4.1 Bicycles - Observations about Bicycles Key Concepts:...

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