I've Got the POWER!

 

When James Watt invented the steam engine he was asked how many horses the engine could replace.  He knew power is measured by the amount of work you can get done per second. 

 

To figure out how his steam engine measured up against horses, he built a device where he measured how long it took a horse to lift various weights.  Watt defined horsepower as the power a horse can produce steadily for a sustained period of time. 

 

                                                              How many "horses" do you have?

 

The Challenge:  Measure your horsepower.

 

The Tools: You need a meter stick and a stopwatch.  When you finish your measurements you'll also need access to a calculator and a laptop.

 

The Tricks of the Trade: These might be helpful when you start your calculations!

Ex: My cat weighs 16 pounds.  What is her mass?

               1 pound  = 16 pounds

                                               0.45kg          ???

Cross multiply and you find my cat weighs 7.2kg!

Ex:  My cat has a mass of 6.5kg and jumps 1 meter high.  How much work did she do?

                                             Work = weight x total height

                                             Work = (mg) x total height

                                             Work = (7.2kg)(9.8m/s2)(1m)

                                             Work = 70.56

 

Directions:

To measure your work, you'll run up the stairs.

Start with both feet on the ground. Have your partner start the stopwatch when both feet have left the ground.  The stopwatch stops when both feet are on the top floor.  Then switch so both partners get a chance to run.  You may repeat this exercise to try and improve your time.

 

Data table:

Name

Mass (in kg)

Height of one stair

Total number of stairs

Time

(in seconds)

 

 

 

 

 

 

 

 

 

 

 

 

 

Calculations:

Determine the work done by each partner.  (Hint: Look at "Tricks of the Trade" for examples.)

Determine each partner's power in watts.

Convert the number of watts to horsepower.

 

Get thee to a computer!

Put your calculations into the excel spreadsheet saved on the Student Share. 

How do I do that?  Connect to server, click 2005, folder: 8th Grade Share.  The document is named 8th grade power lab.

Create a histogram comparing everyone's total horsepower.  Print one copy of the histogram for each team member to be turned in with your questions.

 

Questions:

To be answered on a separate piece of paper as an individual for homework.  Please use paragraph structure, complete sentences and observe the conventions of writing.  This may be hand written or word-processed.

 

  1. What is the relationship between the horsepower and work?  How can you tell?

 

  1. How many horsepower did you have?  Are the results surprising to you?  Why or why not?

 

  1. What are some possible sources of error in this experiment?  What could you do to reduce error if you did this again?

 

Extension:

If you have time remaining, get online and research the average horsepower in cars, planes or any other objects you can think of (maybe even the space shuttle?!?!).  Record your findings.