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WORK!

remy avatar
remy
17 diapositives · 529 Views · Sep 17, 2014

WORK!. What are the different meanings of work? Make it work—to the world The power of work---to science. WORK----the basics. A Force acting in the same direction as motion Force needs to be in Newtons Distance will be in meters Unit of work = Joule = N · m W = F x d. Suppose.

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  1. WORK! What are the different meanings of work? Make it work—to the world The power of work---to science

  2. WORK----the basics • A Force acting in the same direction as motion • Force needs to be in Newtons • Distance will be in meters • Unit of work = Joule = N·m • W = F x d

  3. Suppose • A person whose weight is 238 lbs, can run up a stairway whose height is 60 meters in 200 seconds. Did this person do any work? • What are we given? • wt = 238 lbs = w (lower case) • Height = d = 60 m • Time = 200 s

  4. Calculate the work • W = F x d • W = F (but it is not in newtons!) • We need to stop and do an extra step or two

  5. Newton = kg·m/sec2 • Need Kg instead of lb • Use the conversion line to change the lbs to Kg. 1 Kg = 2.2lbs 238 lbs 1Kg = 108.2 Kg 2.2 lbs

  6. Force = mass x g • mass = wt in kg • g = 9.8 m/sec2 • Force = 108.2kg x 9.8m/sec2 • F = 1060.4 N = 1060N

  7. So now…..how much work? • Work = F x d • W = 1060N x 60m • W = 63600 Joules • Work = W = upper case • Is that a lot? Let’s change this into power units or watts.

  8. Is this high power or low power? • Power = work time • Power = 63600 J / 200 s = 318 W

  9. Watts to horsepower (HP) • 1 horsepower = 746 W • Watt = W = upper case (it is a unit of measure, not a variable) • 318 Watts 1 hp = 0.42 hp 746 W

  10. Page 416 in text • Write answers to #4-6 in your notes • When finished pick up the lab at the front and read carefully. • Complete Part 1 right now • be ready to explain to me how to complete part 2 by the time (15 min from now) written on the board.

  11. Horsepower Lab • Expectations • Work quietly • Teams of three, one timer, one timer and writer, one “worker”. We will trade jobs three times. • Run in alphabetical order, 4 at a time. • Take with you/team • 2 pencils • Each person’s lab • 1 metric ruler • 2 stopwatches

  12. Turn your labs upside down • Take out your answers to #4-6, you will self-check

  13. Answer to #4 • The supporting force does no work because the object is not moving. The object in this case is the computer, it is not moving.

  14. Answer to #5 • The car with the more powerful engine will reach the top first. • However, keep in mind….both cars do the same amount of work

  15. Answer to #6 • Carrying one bag at a time uses only half the force, but requires the force be applied through 2X the distance. • The work done is the same, carry 1 or 2 it is your choice.

  16. Complete the lab • On your own, no talking. • Raise your hand if you need help. • Lab is due at the end of class • Pick up homework: 14.6-problems on back, due tomorrow

  17. Tests back tomorrow • Grade printouts today • If grade is 3, 4, or 5 you need to have a parent sign the printout and return by THURSDAY (12/4) • Any missing assignments need to be turned in by Dec 9th, or they become a zero. • Overall----GREAT improvements in this class! • Keep up the wonderful effort and stay focused on details!