The lab activities are required for this course.  If you missed the first lab session, you need to complete the activities below and hand in this sheet by Thursday April 15, 2004 before you perform the next lab

 

Part 1:  Do activity 2 on page 92 in the textbook.

 

Part 2: Human Power and the Watt!

 

Introduction:

 

Power is the rate of energy use or the rate of doing work:

 

                        Power  = Energy/time

 

The unit of power in the metric system is the watt.  Energy is used at a rate of one watt if one joule is used per second.  Some useful conversion factors for other units of power are:

 

                        1 watt = 1 joule/sec

                        1 kilowatt (kW) = 1000W = 103W

                        1 megawatt (MW) = 106W

                        1 ft-lb/sec = 1.36W

                        1 horsepower (hp) = 550 ft-lb/sec = 746W

                        1kg mass = 2.2lbs: So a 220 lb person has a 100kg mass

                        3.2ft = 1 meter

 

  1. How many horsepower can you generate?  Walk up a flight of stairs and record the time it takes. Then Run up a flight of stairs and record the time.  In going up the stairs, you have gained gravitational potential energy equal to your weight in pounds times the height of the stairs in feet. (Another option is to use your mass in kg multiplied by 10m/s2 and divide by the time which will give you watts).

 

Thus the power rate is

 

Power  =(weight)x(height)/time= _____ ft-lbs/sec

 

What is your power output in watts and horsepower?

 

                                                                                    Watts

 

_____________ hp

 

Calculate the power for walking up the stairs and running up the stairs and compare the results. What can you say about the energy and power differences in running and walking?

 

 

Time in seconds

Power in Watts

Walking Up Stairs

 

 

Running Up Stairs

 

 

 

B. (HOMEWORK)   How do you compare to a 100 watt light bulb?  A human being must take in about 2500 Calories (kilocalories) of energy in his or her food each day in order to continue to function properly.  This means that he or she uses up energy at a rate of (power) of 2500 kilocalories/day.  Using the fact that 1 calorie = 4.2 joules, and the appropriate time conversions show that this rate of energy usage is about the same as a 100 watt light bulb.

 

 

 

 

 

 

 

 

 

 

 

 

            Compare this result to Part I.  Why are they different?

 

 

C.  (Homework) The table below lists the rate of energy use by a human being during various activities.  Calculate the power rating of your body pursuing one of these activities in watts and horsepower.  ( Remember that 1Cal = 1kcal = 1000cal)

 

Table 1. Energy expenditure rate in various activities in of body weight.

Sleeping                                 0.45

Walking (2.8 mi/h)                  1.5

Sitting still                               0.6

Carpentry, plumbing                1.75

Standing relaxed                      0.7

Active exercise                         1.9

Sewing by hand                       0.75

Walking fast (4 mi/h)              2.0

Dressing, undressing               0.8

Going down steps                   2.25

Singing                                    0.85

Loading heavy objects              2.5

Typewriting                             0.9

Heavy exercise                        2.75

Washing dishes, ironing          0.95

Tennis, swimming                   3.25

Sweeping                                 1.0

Running (5.5 mi/h)                  3.75

Light exercise                          1.25

Very heavy exercise                4.0

Going up stairs                        7.0

 

 

 

 

 

 

 

 

 

 

How does this compare to the power rating you measured in Part A?

 

PART 3:  Energy in One Form or Another

 

ENERGY CONVERSION

 

We have discussed most of the following types of energy:

 

Type of Energy                                   Abbreviation

 

A.  Kinetic Energy                                           KE

B.  Gravitational Potential Energy                   GPE

C.  Chemical Potential Energy                         CPE

D.  Elastic Potential Energy                             ELPE

E.  Potential Difference or Voltage                  V

F.  Magnetic Potential Energy                         MPE

G.  Electromagnetic Radiation (Light)             ER

H.  Heat or Thermal Energy                            H

 

There are several energy conversion devices in the lab room.  Your job is to analyze each, and write down all of the energy conversions involved in the operation of the device.  Use the abbreviations from above and follow the example (1) below.

 

1.  Mass oscillating on a spring

    ELPE --> KE --> GPE --> KE --> ELPE --> repeat until all the motion is turned into heat and the oscillation stops.

 

2.  Pendulum

 

 

3.  Electric Clock

 

 

4.  Wind-up toys

 

 

5.  Incandescent Light Bulb

 

 

6. Super ball, or any ball that bounces: Throw the ball up and describe the conversions from after the ball is released.

HOMEWORK:  SOME MORE CHALLENGING ENERGY CONVERTERS:

 

1.  Try to write down the overall energy conversion involved in the operation of the following devices which you come in contact with every day; i.e., what type(s) of energy is put in and what comes out?

 

                                                                        ENERGY IN               ENERGY OUT

 

A.  Television

 

B.  Toilet

 

C.  Clothes Dryer

 

D.  Jet Taking off

 

 

2.  List the energy conversions that take place in an automobile engine.

 

 

 

 

3.  What happened to the kinetic energy of a moving automobile that was moving and stopped? What happens to the energy in sound waves from a radio when the sound is turned off?  What happened to the kinetic energy of a pendulum bob as it slowed down and came to rest?