Physics/Dr. Lankar                  Name: ________________ section: ______________: %: _______
LAB POWER
WORK and POWER - Compute the “Horse power” in you!


PURPOSE
 
To understand the difference between power and work. To convert the work done in horsepower.
 
DISCUSSION - FILL BLANKS
  When you are climbing the stairs, you are doing work against the pull of ________ . You gain potential ________ as your height increases and as your are lifting your own _______. You burn  your chemical energy (fator sugar) to do gain _________ energy.
The work done (ENERGY spent)  is equal to |force applied x distance| = your _______   x height climbed with weight(N) = _____ (Kg) x ____ (m/s/s)
so WORK (J) = ________ (N)  x ________ (m)


If you climb the stairs running up or walking up you are doing the same _______________.
(because same weight, same height).  However, 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 ___________.
 
The rate at which work is done is called POWER noted P (rate here  is energy produced per second)  
In the system international, work is in ________  (J) , time in _______ (s) and POWER  in watts (W).
POWER (in watts) = WORK (in joules) / TIME (in seconds)   or for short    P  = W  / t 
When you are climbing the stairs :  WORK = WEIGHT x HEIGHT so

POWER =  ___________________________  (use power = work / time  with work = weight x height)
IF YOU RUN up the stairs instead of walking, you are PRODUCING MORE __________ eventhough the energy burn is the SAME.
 
When the steam engine was first invented there was a need to describe the rate a which the engine could work.
(how much energy burnt per second  or how much coal burnt in 1 second)
Since people at that time were familiar with using horses to do their work, the steam engines were compared to _________.
James Watt, who designed a workable steam machine engine, defined horsepower (hP) as a power rating of 550lbs ft/s.

That is horse can  lift 550lbs , over a height of 1ft in one second.
People could then compare the new steam machines to the familiar power of a horse:

An average horse can lift 550lbs over 1 foot in 1 second.
If you convert to joules you get a rate of
746 joules per second.
A horse produces _______ J per second or simply
746 watts.
A horse power is a another unit for power.
1 horse power = 746 watts.
It is always fun to convert power to hp to compare your power
or the power of a machine  to a __________


PROCEDURE
you need a bathroom scale, stairs case, meter stick, stop watch on line

USE A STAIR CASE. USE 2 floors.  

Step1: Teams of two students will measure the work done, the rate at which work is done, and the horsepower rating as they move up a staircase.
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.  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. (  1 foot = 12 in)
 
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..

person Aperson Bperson C
walkingrunningwalkingrunningwalkingrunning
weight (in pounds))
vertical height
(in number of stairs)
vertical height in feet
(height of 1 stair x number of stairs)
time (required in seconds)
work required
 (weight in lbs  x height in ft)
Power = work (ft lbs) / time (s)
horse power = power / 550
how many horses in you ?
convert last row number in fraction. use TI

ANALYSIS
 
1. Why there is a difference in the horsepower developed in walking and running up the flight of stairs.
  
 2. Who is the class is able to produce the more horse power ? and the least ? why do you think so ?


3. Is there some limit of  the horsepower developed ? Why ?
 
  
4. 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.
 
 
5. Was the purpose of this lab accomplished ? Why or why not? describe what you learnt.

 

 


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