lecture22 - acceleration will be the same for two objects...

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Lecture 22: Examples with Three Principles 1 Summary - Three Fundamental Principles Here they are: 1. Momentum Principle 2. Energy Principle 3. Angular Momentum Principle Also recall that we have now learned two ways to solve problems 1. Conservation Laws Identify system and identify what’s conserved Write one equation for each conserved quantity If # equations = # unknowns, solve! If not, make sure you haven’t overlooked a conserved quantity. If you have not, you cannot use conservation laws to solve the problem. 2. Newton’s 2nd Law, Newton’s 2nd Law for rotation Draw a free body diagram for each object to identify all forces For each component (x, y, or z), write ~ F = m~a or ~ τ = I~ω . If # equations = # unknowns, solve! If not, look for and apply any constraints (e.g.
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Unformatted text preview: acceleration will be the same for two objects attached by a rope). Then solve • The key to solving problems is identifying which method to use. In general you should try to use conservation laws ±rst. One exception is if you are asked to solve for the value of a force. • Some problems will involve both linear motion AND rotational motion! THE ONLY WAY TO GET GOOD AT THIS IS TO PRACTICE DOING PROBLEMS! 2 Examples • conservation of angular momentum only - pinned meter stick??? • Puzzlers - what’s conserved? Discuss conservation of energy and ice skater again. • Falling meter stick • Rolling without slipping/cylinder rolls down incline with puzzler ±rst • Auto wheel? or one from last year ±nal 15...
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