Online Lesson Plan “Finding” Horsepower
Lesson Plan by who has taught science at both the middle school and high school levels for Lincoln Public Schools. She has written assessment and curriculum for LPS and has attained a Level II assessment certification. She has also served as a student teacher supervisor for the University of Nebraska-Lincoln.
| Subject Area: Science |
Suggested Grade Level: Grades 6-8 |
| Learning Modality: Kinesthetic |
Multiple Intelligence: Logical-mathematical & Naturalist |
| Bloom’s Taxonomy: Application |
 What are these educational concepts? |
Objectives
In this lesson, students will:
- investigate horsepower as a unit of power;
- calculate horsepower from a set of given data;
- and look at history and discover that scientists and engineers of high achievement are considered to be among the most valued contributors to their culture.
Introduction
The engineer, James Watt, invented the term “horsepower.” Watt lived from 1736 to 1819 and is famous for his work on improving the steam engine. Watt was working with ponies lifting coal from a mine and wanted to devise a way to describe the amount of power they exerted. A Watt as a unit is used to measure all power whether it is mechanical or electrical.
Power is the rate of doing work. It is a measure of how quickly a job can be done. You can calculate power by dividing the work done by the time it takes to do it. The unit is foot-lbs/second.
Horsepower is a unit of power. Power has units of energy per unit time (P = W/t), and is measured in watts. One watt is one joule of work done in one second. The joule measures energy in physics in meters/kilogram/sec. And one horsepower equals about 746 watts. If you took a one horsepower horse and put it on a treadmill, it could power a generator and produce a continuous 746 watts.
One horsepower equals measuring how much power a horse could deliver.
Although one horsepower equals 746 watts, according to current engineers, a more reasonable number for a horse working an eight-hour day is probably about 500 Watts. If Lance Armstrong (or another cyclist) could do 500 watts output power on a stationary bike, he would be considered strong as a horse! To help you understand the measurement, a bright light bulb draws about 100 watts, a microwave oven, 1000. A person uses food energy at an average rate of 100 watts.
The Resources
Links from within the Wessels Living History Farm site. [Note that clicking on these links will open a new browser window. Just close it and you’ll be back to this page.] Direct the students to these pages.
- Horses Finally Lose Their Jobs
- Tractor Innovations
- International Harvester Farmall Tractors
- Allis-Chalmers Tractors
- John Deere Tractors
- Ford-Ferguson Tractors
- Case Tractors
Resources from outside Wessels. Direct students to these Web sites that are produced by others outside of the Wessels Living History Farm. [Again, clicking these links will open a new window.]
The Process
If you want to know the horsepower of an engine, a dynamometer is used. It places a load on the engine and measures the amount of power the engine can produce against the load. The tractor testing labs at the University of Nebraska tractor test site determined the maximum horsepower of the engines below.
If you plot the horsepower versus the rpm values for the engine, you get a horsepower curve for the engine. Peak horsepower for an engine is when the rpm value available form the engine is at its maximum. Torque is a measure of turning force, or said another way, a measure of how much a force acting on an object causes that object to rotate.
Dynamometers actually measure torque (in pound-feet). To convert torque to horsepower, you multiply torque by rpm and divide by 5,252. The number 5,252 is the result of lumping several different conversion factors together.
Using the information in the chart below, calculate the horsepower for each of the six tractors. Use the maximum number of revolutions per minute.
| Type | RPM min. | RPM max. | Torque | Horsepower “hp” |
| Allis 5650 | 1305 | 1850 | 123.6 lb-ft | |
| John Deere 5105 | 1402 | 1801 | 114 lb-f | |
| Massey Ferguson 243 | 1248 | 1789 | 133 lb-ft | |
| Massey Ferguson 263 | 1321 | 1790 | 161.8 lb-ft | |
| Massey Ferguson 2220 | 1498 | 1800 | 169 lb-ft | |
| Case IH DX48 | 1602 | 2206 | 96 lb-ft |
Learning Advice
Other tractor data may be obtained from TractorData.com.
Teachers may wish to assign other problems solving for work or power from their classroom textbook.
Teachers could easily add this information to a physical science unit on work/power/watts and efficiency.
Conclusion of the Lesson
For nearly 200 years, the horse was the only supply of power on the farm. Until tractors were developed and used, the workhorse supplied the power to pull farm implements over every acre of soil planted. If farmers had to rely on horsepower to produce food today, our nation would need 20 times the number of existing horses, and five times the number of farm workers!
Assessment Activity
| Question 1: What is the difference between work and Power? Work and energy? |  |
| Question 2: The words “work” and “power” are used in many ways in everyday language, but have very specific meanings in science. Write a sentence using work and power in a scientific way. | |
| Question 3: James does 2400 Joules of work climbing the stairs in 6 seconds. What is his power output? | |
| Question 4: How do machines make work easier? | |
| Question 5: Prepare a short report on the life of James Watt, Henry Ford, or Harry Ferguson. What was their family background? What life events led them to their success? Were they ever unsuccessful? What was their educational background? What was their contribution to science? | |
| Question 6: Torque is measured in “foot-pounds.” Research other units that you may be unfamiliar with. Include their meaning and what science they represent. | |
| Question 7: Chart or graph the power to weight ratio (horsepower divided by the weight) of the following tractors: |
| Tractor Type |
Horsepower (hp)
|
Weight (lbs)
|
Years Built
|
Cost
|
| Case IH DX48 | 25 | 3,700 | (unavailable) | (unavailable) |
| J.I. Case SC | 19 | 4,200 | 1940-1955 | $1,700 |
| Case IH 9390 | 400 | 29,000 | 1997-1999 | $160,000 |
| Allis Chalmers 8070 | 150 | 13,750 | 1982-1985 | $60,000 |
| John Deere M | 25 | 2,550 | 1947-1952 | $1,075 |
| John Deere 5320 | 50 | 4,550 | 2000- | (unavailable) |
| Ford 2N | 24 | 3,070 | 1942-1947 | $1,120 |
| Ford 5900 | 50 | 5,760 | 1985-1993 | $17,400 |
| Ferguson TE20 | 224 | 2,760 | 1946-1956 | (unavailable) |
As you study the data from the horsepower chart, is there a correlation between the horsepower and the weight of the tractor? Is there a correlation between the weight and the cost of the tractor? Explain.
Can you estimate the cost for the missing data above based on the other information on the chart?
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