Horsepower Lab

Background: Power is the rate of doing work. Work is Force x distance. Power is Work/ time. A simple way to measure power output of a person is to measure the time it takes the person to run up a flight of stairs of known height. This value can then be converted from the metric unit of Watts into the English value of horsepower.

When James Watt invented the steam engine, he was asked how many horses the engine could replace. To find out, Watt built a rope and pulley device with which he could measure the time it took a horse to lift various weights 1 yard. After many experiments, Watt concluded that the horse could produce 550 ftlb/s of power, or 746 watts for a sustained period of time. This is now the standard for one horsepower. Although Watt used English units of measurement in his experiments, it was the metric unit of power which was later name in his honor. Watt’s definition of horsepower is still used today even though the power output of today’s average horse during the course of a working day is only about two-thirds of a standard horsepower.

Purpose: Determine the horsepower of a student walking and running up a flight of stairs.

Formulas:

· F=mg (Force = mass x gravity) *units measured in Newtons

· W=Fd (Work = Force x distance) *units measured in Joules

· P= W/t (Power = Work / time) *units measured in Watts

Conversions:

· 2.2 lbs = 1kg

· 0.3048 meters = 1 foot

· 1 hp = 550 ft/lbs

· 1 hp = 746 watts

Procedure:

1. Use the formulas, conversions and data chart to help you calculate the horsepower of a student walking and then running up the stairs. You will perform these calculations in English and Metric units. When you a finished, all the blanks in the data chart should be full.

2. Answer the conclusion questions that follow.

Data Chart:

Calculation / Ascending Stairs Slowly / Ascending Stairs Quickly
Metric / English / Metric / English
Height of one step / 0.17 meters / ______feet / 0.17 meters / ______feet
Number of steps / 13 / 13 / 13 / 13
Total Vertical Height / _____ meters / ______feet / ______meters / ______feet
Time of Climb / 7.6 sec / 7.6 sec / 3.2 sec / 3.2 sec
Force / _____ N / 150 lbs / _____ N / 150 lbs
Work (W=Fd) / ______J / _____ ftlb / _____J / _____ftlb
Power (P=W/t) / ______Watts / _____ftlb/sec / _____Watts / _____ftlb/sec
Horsepower / ______Watts / ______ftlbs/sec / ______Watts / ______ftlbs/sec

Conclusion:

1. How would a person’s horsepower change if they did a job more quickly?

2. How would a person’s work change if they did a job more quickly?

3. How would a person’s horsepower change if you strapped a 50 lb weight on their back?

4. How strong is the person portrayed in the data chart compared to a horse? Be sure to describe their strength when they are walking and when they are running.