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Power and Work

Power and Work. Background Information. Work (scalar) : Force exerted over a distance. Unit is Joule (J) Power (scalar): The rate at which work is done. Unit is watt (W). Work vs. Power. Lifting an object slowly and quickly to the same height Both have the same amount of work done

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Power and Work

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  1. Power and Work

  2. Background Information • Work (scalar): Force exerted over a distance. Unit is Joule (J) • Power (scalar): The rate at which work is done. Unit is watt (W)

  3. Work vs. Power • Lifting an object slowly and quickly to the same height • Both have the same amount of work done • Slowly has less power • Quickly has more power

  4. Power and Work Lab

  5. Objective: • To determine how much work and power is done in physical exercises.

  6. Hypothesis:(write the questions and answer them) • Do you think physical exercises will produce powers greater or smaller then a light-bulb? • Do you think physical exercises will produce powers greater or smaller then a lawn mower engine?

  7. Materials: • Meter stick • Stopwatch • Books or other weights (Return all materials back to the cart up front when finished)

  8. Procedures:Record your own exercises! • Choose an exercise that involves doing work against the force of gravity. • Measure the distance that you exerted the force. • Enter your measurements in a data table. • Now, perform several repetitions (5 or 10) of the exercise as fast as you can (while being safe!). Have your lab partners count the repetitions and measure the total time it takes. • Repeat for three more exercises. Use two exercises that use arm muscles, and two exercises that use leg muscles.

  9. Examples of Exercises • lifting an object (arm) • raising on toes (leg) • arm curls (arm) • knee bends (leg) • push-ups (arm) • jumping jacks (leg) • etc.

  10. Exercise Data Table

  11. Conversions: • You will need the weights in Newtons for this activity, the force of gravity pulling down on the object. • Book = 1.5 kg • (1 pound = 4.45 Newtons) • (Fg = m · g)

  12. Calculations (T-Charts) • Calculate the work done in one repetition for each exercise. ( W1 = F · d ) • Calculate the total work done for each exercise. ( Wtotal = W1 × [# of reps] ) • Calculate the power done for each exercise. ( P = Wtotal / t )

  13. Conclusion: • How does the power output of your arm muscles compare to the power output of your leg muscles? Why do you think this is? • How does your power output compare to the power output of a 18 watt fluorescent bulb? • How does your power output compare to the power output of a lawn mower engine? (about 750 watts)? • Is the power output of your muscles more or less than you thought it would be? (Hypothesis) • Did the activity that used the largest force result in the largest power produced? • Explain how a large force can result in relatively small power. • What is the relationship between work and power? • What is the relationship between mass and weight?

  14. Exercises (5 Reps for each exercise) Arm curls Push ups Jumping jacks Knee bends Distances Arm curl = 43 cm Push up = 19 cm Jumping jack = 1.5 cm Knee bend = 32 cm * Covert cm to m * Time for five reps Arm curls = 3.25 s Push ups = 5.13 s Jumping jacks = 6.79 s Knee bends = 4.83 s Find the force of gravity (weight) in Newtons Weight = 2.5 pounds (arm curls) Your weight in pounds (for all the other exercises and ½ you weight for push ups) (1 pound = 4.45 Newtons) Make-up Data

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