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Work & Power

Work & Power. Chapter 8.1. How do you define “work,” or what comes to mind when you hear that word? How about the word “power,” anything else?. I. What is Work? A. Definition B. Equation C. Unit II. What is Power? A. Definition B. Equation C. Unit. III. Machines A. Forces

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Work & Power

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  1. Work & Power Chapter 8.1

  2. How do you define “work,” or what comes to mind when you hear that word? • How about the word “power,” anything else?

  3. I. What is Work? A. Definition B. Equation C. Unit II. What is Power? A. Definition B. Equation C. Unit III. Machines A. Forces B. Input/Output C. Mech. Advantage 1. Definition 2. Equation IV. Math Skill Practice A. Work B. Power C. Mechanical Advantage Chapter 8.1 Outline

  4. What is Work? • Non-science definitions • Definition: • The effect of a force acting over a distance • Examples • Non-Examples

  5. Calculating Work • Equation: work = force x distance W = F x d

  6. The Units of Work W = F x d unit = kg*m2/s2 unit = N*m unit = J(joule) Example: Three push-ups require about 1000 J of work

  7. What is Power? • Non-science definitions • Definition: • The rate at which work is done • Examples

  8. Calculating Power • Equation: power = work/time P = W /t

  9. The Units of Power P = W /t unit = J / s unit = W(watt) Example: Three push-ups done in 3 sec. is about 330 W of power

  10. Machines • Why do we use machines? • Which is easier, lifting a car by hand or using a car jack? • Which requires more work? Key Statement: Machines multiply and redirect forces.

  11. Machines and Work • The work that you put into a machine equals the work put out by a machine • What things qualify as machines? • p.254 – Figure 8-3 Key Statement: Work input equals work output

  12. Mechanical Advantage • Definition: • A measurement of how much a machine multiplies a force or distance In other words, how much is the machine benefiting you?

  13. Mechanical Advantage • The Equation: Mech. Adv. = output force = input distance input force output distance It is a ratio, therefore there are no units attached

  14. You and two friends apply a force of 425 N to push a piano up a 2.2 m long ramp. How much work in joules has been done when you reach the top of the ramp? W = F x d = 425 N x 2.2 m = 935 J = 940 J If you make it to the top in 5.0 s, what is your power output? P = W / t = 940 J / 5.0 s = 188 W = 190 W If lifting the piano straight up would require 1700 N of force, what is the MA of the ramp? MA = output F/ input F = 1700 N / 425 N = 4.0 Math Skills – Putting it all together!

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