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Chapter 6 Energy and Oscillation

Chapter 6 Energy and Oscillation. Energy, Work, and Power Energy = ability to change the condition of matter When you add energy to a system, something must change Heat is a form of Energy Heat a beaker of water Motion of the water as it boils Vaporization of the water into steam

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Chapter 6 Energy and Oscillation

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  1. Chapter 6 Energy and Oscillation • Energy, Work, and Power • Energy = ability to change the condition of matter • When you add energy to a system, something must change • Heat is a form of Energy • Heat a beaker of water • Motion of the water as it boils • Vaporization of the water into steam • Push down a spring—the spring changes shape then snaps back • Move a suspended pendulum, it starts swinging back and forth • Simple Machines = multiply the effect of an applied force • Make it easier to change the condition of a system • Lever • F1d1 = F2d2 • Same Energy • Smaller force over larger distance

  2. 3) Pulley • Use half the force to move the object • Pull twice the length of rope • Same energy, less force • Mechanical Advantage = • Work • Force applied and the distance moved tell us about what happens when we add energy to a system • Work = W = Fd Units = N x m = Joule = J = units of Energy • Work is a form of energy and has units of Joules (J) • Only the component of the Force in the direction of the movement counts • Since no movement vertically work is done only horizontally • If you push on a wall that doesn’t move have you done any work? W? 2 m

  3. Power = measure of work done per unit time 1) • W = 200 J t = 10 s P = 200 J/10 s = 20 J/s = 20 Watts • 1 J/s = 1 Watt = 1 W 1000 W = 1 kW • 1 hp = 746 watts = 0.746 kW • Kinetic Energy = Energy associated with motion • Work involves transfer of energy to a moving object (from you to a box) • W = Energy transferred = F x d implies motion • F causes acceleration • As the velocity increases, distance is covered at a faster rate • Apply same F, but distance increases • Energy increases with velocity W = weight = work = Watt Find W and KE for m = 100kg v = 2 m/s F = 50 N d = 4 m If velocity doubles, KE quadruples

  4. Negative Work • A car stopping is losing Kinetic Energy = negative Work • KE = negative = W • Friction opposing motion is the force slowing down the car (-f) • Stopping distance • Remember W = KE directly proportional to v2 • Double velocity, we quadruple work required to stop • Braking power (friction) is constant • A car going twice as fast takes 4 times farther to stop

  5. Potential Energy • Lifting a weight up to a higher position • We have performed work on the box • KE at the end is still = 0 if its not moving • What happened to the Energy we transferred? • Gravitational Potential Energy = stored energy depending on how far from the Earth’s surface an object is • W = F x d = PE = (weight)(height) = mgh • PE = mgh • Work is performed by pulling against the force of gravity D) What happens when we drop the box? • Potential Energy is turned into Kinetic Energy • Call ground h = 0 PE = mgh = 0 • Box 6.3 PE? m = 100 kg, h = 2 m KE? Friction and Heat

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