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lec16b

# lec16b - Lecture16 P112 Feb25,2008 WorkandEnergy...

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Lecture 16 P112 Feb 25, 2008

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Work and Energy Today: new concept energy Want to relate forces acting on objects to changes in kinetic energy Reason: significant shortcut to many problems Energy is (one of) the most important and fundamental concepts in physics
Motion with constant acceleration Eliminate t: Involves speed (internal) Involves position (external)

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Relating internal changes to external changes Convenient to scale by mass: F Change in “kinetic energy”= Work done on object Units: 1 Joule = 1 Newton x Meter
Quick questions Person lifts a barbell, holds it up, and lowers it again. What is the work done by the person on the barbell during this process?

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Work in 3D v a Does speed change?
Work in 3D v a Does speed change? No: tangential accel changes speed -- radial accel just changes direction A force perpendicular to direction of motion does not change speed: does not change kinetic energy

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Work in 3D Define: Work = component of of force along displacement times displacement Reason: This gives change in “kinetic energy”
Definition of Work When a constant force F acts on a particle that undergoes a straight-line displacement s , the work done by the force on the particle is defined as Units: 1 Joule = 1 Newton x Meter

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lec16b - Lecture16 P112 Feb25,2008 WorkandEnergy...

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