Cycle II Regents Physics

John Dewey High School

Mr. Klimetz

In this particular exercise you are going to

evaluate the role of forces in doing work,

explore the physical and mathematical relationship between work and power,

determine how power is calculated, and

convert between SI and English units of power measurement.

Bathroom scale

Meter stick (or metric measuring tape)

Stopwatch

1. Locate a straight staircase at least 3.5 meters in vertical height and preferably with a handrailing. There should also be a clear area of at least two meters at both the top and bottom of the stairs. Measure the height of one single riser (step face) and multiply this by the total number of steps and record. This is your total displacement over which work will be done.

2. Use the bathroom scale to measure the weight of each person in your group. Since the bathroom scale is calibrated in English units you must convert the bathroom scale reading reading to metric units (N). Note that 1 pound equals 4.45 N.

3. Set the stopwatch chronometer function to zero. Ask the first member to then run up the stairs between adjacent floors (first floor to second floor or second floor to third floor) as fast as possible. (Remind all your fellow students before beginning their run to grasp the handrailing for safety as well as for added power during their ascent.) Commence timing when both of each runner's feet have left the floor upon which they began their trip and stop the timing when both feet are on the top floor of the landing at the end of their trip. Record the time in seconds.

4. Repeat the procedure for each group member. Record all data. Some team members may wish to repeat their trials to improve their travel times.

5. Perform all calculations and conversions.

6. Answer all questions at the end of the exercise.

Name

__________

__________

__________

__________

__________

__________

wt (lbs)

wt (N)

Trial 1

Trial 2

Trial 3

Avg.

Time

(s)

Time

(s)

Distance

Run

(m)

Work

Done

(J)

Power

Generated

(W)

Power

Generated

(hp)

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1. Use the following equation to compute the power output (in watts) of each group member listed in the data table:

P = (**F** x **d**)/t

where P is power (watts), **F** is applied force (newtons), **d** is displacement traveled in the direction of the applied force (meters) and t is time (seconds). Record where indicated.

2. Convert the wattage of each participant into horsepower equivalents and record.

1. What is the relationship between the horsepower of the participants in this experiment and James Watt's definition of the horsepower? In other words, compare the calculated horsepower readings of each group member.

2. List potential sources of error in this experiment.

3. How does this experiment illustrate the relationship between force, displacement, and time in the power equation?

4. What should a graph of force versus distance resemble if we were to run up different flights of stairs of different heights? Sketch the presumed relationship, assuming that we were running at top speed and we never ran out of energy. To what is the area beneath the plotted line equivalent? (Think!)