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PHYS16 – Lecture 18

PHYS16 – Lecture 18. Ch. 8 Energy Conservation. Ch. 8 Energy Conservation. Conservative vs. Non-conservative Forces Conservation of Energy Basic Equations Systems without Friction Systems with Friction Power. P16 at the Circus… … Continued. Motorcycles, Flames, and Loops.

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PHYS16 – Lecture 18

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  1. PHYS16 – Lecture 18 Ch. 8 Energy Conservation

  2. Ch. 8 Energy Conservation • Conservative vs. Non-conservative Forces • Conservation of Energy • Basic Equations • Systems without Friction • Systems with Friction • Power

  3. P16 at the Circus…… Continued

  4. Motorcycles, Flames, and Loops • What is speed at end of ramp E? 23 m/s

  5. Discussion Question • When is kinetic energy negative? • When is work negative? • When is potential energy negative? • Give some examples of each… Never!

  6. When is work negative? • Work is (+) when done on system, (-) when done by system • Work is (+) when force and displacement in the same direction, (-) when in opposite directions

  7. When is potential energy negative? • Potential is (+) when movement and force are in opposite directions (-) when movement and force are in same direction • Potential is (+) when external work is (+)

  8. Power

  9. Let’s define Power • Power – the rate at which work is performed • Units = W = J/s • Scalar

  10. Lingenfelter Corvette… • What is the power of the 1420 kg Lingenfelter Corvette that can go 0 to 26.8 m/s in 1.97 s? Approach #1 Approach #2 Answer = 259 kW Spec says 1100 kW, why?

  11. Horsepower • 1 hp = 33,000 ft lbs/min = 746 W • Comes from how much weight a horse could pull up a mine shaft a particular amount of feet in a given minute Horse Force

  12. Estimating horsepower • Car = 250-1475 hp • 1 hp = 746 W • Lingenfelter corvette = 1475 hp • Small compact= 250 hp • Lawnmower = 5-25 hp • Person = ~1 hp • Estimate using time it takes to run up stairs

  13. Conclusions • Conservative vs. Nonconservative Forces • Energy Conservation • Power

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