LAB: WORK and POWER - Compute the “Horse power” in you!

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PURPOSE

 

To understand the difference between power and work. To convert the work done in horsepower.

 

DISUSSION

 

When you are climbing the stairs, you are doing work against the pull of gravity. You gain potential energy as your height increase and as your are lifting your own weight. You use your chemical energy to do that transfer. The work done is equal to weight (yours) x height climbed.

 

If you climb the stairs running up or walking up you are doing the same _______________.

(same weight, same height). You feel more tired if you run because:

THE RATE AT WHICH ENERGY IS TRANSFERRED IS GREATER.

THE RATE AT WHICH WORK IS DONE IS GREATER.

YOU ARE GETTING THE JOB DONE IN LESS TIME.

 

The rate at which work is done is called power (P). P = W / t.

In the system international, work is in joule, t in time and P in watt.

 

When the steam engine was first invented there was a need to describe the rate a which the engine could work. Since people at that time were familiar with using horses to do their work, the steam engines were compared to horses. James Watt, who designed a workable steam machine engine, defined horsepower (hP) as a power rating of 550ft lbs/s.

A horse has the power to lift 550lbs , over a height of 550ft in one second. People could then compare the new steam machines to the familiar power of a horse:

 

 

 

 

 

 

 

 

In SI units, power is measured in joules per second, called the watt (W) .

It takes 756 W to equal 1 hp.

 

PROCEDURE

 

Step1: Teams of two volunteers will measure the work done, the rate at which work is done, and the horsepower rating as they move up a stairwell. Person A will measure and record the data for person B. Person B will measure and record the data for person A. An ordinary bathroom scale can be used to measure each person’s weight. Do that at home. Record the weight in pounds (lb) in table 1. This weight is the force (F) needed by each person to lift himself or herself up the stairs

 

Step2; The vertical height of the stairs can be found by measuring the height of one step, then multiplying by the number of steps in the stairs. Record the distanced d in feet (ft) in TABLE1.

 

Step3: Measure and record the time required for each person to walk normally up the flight of stairs. Record the time in seconds (s) in TABLE 1.

 

Step5: Calculate the work accomplished, power level developed, and horsepower of each person while walking and while running up the flight of steps. Be sure to include the correct units when recording the data in TABLE 1..

 

 

ANALYSIS

 

1. Why there is a difference in the horsepower developed in walking and running up the flight of stairs.

 

 

 

 

2. Is there some limit o the height of the flight of stairs used and the horsepower developed ?

Why ?

 

 

 

 

3. Describe an experiment that you could do to measure the horsepower you could develop for a long period of time rather then for a short burst up a stair case. (see picture above for inspiration)

 

 

 

4. Was the purpose of this lab accomplished ? Why or why not

Who developed the more power ? ______________________

PLEASE READ THE DISCUSSION BEFORE DOING THE LAB !!