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Power!

Power!. We ’ ve talked about “ work ” , now let ’ s talk about “ power ”. “ Work ” Refresher. Remember that the formula for finding the amount of work done upon an object is: W = (F)*(d) W = the work done F = the force required to cause displacement d = displacement of the object.

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Power!

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  1. Power! We’ve talked about “work”, now let’s talk about “power”

  2. “Work” Refresher • Remember that the formula for finding the amount of work done upon an object is: W = (F)*(d) • W = the work done • F = the force required to cause displacement • d = displacement of the object

  3. Definition of Power • Common definition usually includes something about strength • Physics definition - the timed rate at which work is done • depends directly upon the work and inversely upon the time to do that work If you increase work, then you increase power BUT If you increase time, then you decrease power

  4. How Hard Are You Working? • The rate at which work is done is called power: (Power) = (Work Done) / (Time Spent Working) P = W / t • Power is “how hard” something is working.

  5. Units for power: 1 J 1 s = 1 W one watt (W) equals one joule (J) per second (s) joule per second = watt

  6. Horsepower • Another common unit of power (not used in science, but used in everyday life) is the “horsepower” – basically the rate at which a (very powerful, very healthy) horse can do work over a 10 hour “work day.” • 1 horsepower (hp) = 746 W

  7. How fast can your car do work? • A compact car may have a 120 hp engine. • That means the car’s power is (120 hp)(746 W/hp) = 89,500 W • So a typical compact car can do 89,520 J worth of work each second.

  8. Work & Power Example You are pushing a very heavy stone block (200 kg) across the floor. You are exerting 620 N of force on the stone, and push it a total distance of 20 m before you get tired and stop. How much work did you produce? G: m= 200 kg E: W = f x d S: W = 12400 J F = 620 N d = 20m U: W S: W = (620N)(20M) Let’s say that it took you 40 s to move that 200 kg stone block the 20 m. How much power did you generate? G: m= 200 kg E: P = W / t S: P = 310 Watts W = 12400J t = 40 s U: P S: P = 12400J / 40 s

  9. Fast work isn’t more work • Go back to our 200 kg block example. Remember that when it took us 40 s to push the block the 20 m when we applied a force of 620 N, that implied that we had a power output of 310 W. • If we exerted the same force (620 N) and pushed the block the same distance (20 m), but took half as long to do so (20 s), our power output would double to 620 W.

  10. Fast work isn’t more work • Notice the total work done doesn'tchange – we still exerted 620 N of force over a distance of 20 m. • Make sure you put the following sentence in your notes: • So increasing power output doesn't mean you’re doing more work, it means you’re doing the work faster.

  11. Power Humor • Who is the most powerful teacher on this planet? • Ms. Watts • What did the baby light bulb say to the momma light bulb? • I wuv you watts!

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