Download Work/Power/Energy Lab

Thompkins: Physics Lab
Work/Power/Energy Lab
Purpose
• To determine the work and power required to walk and then run through one floor
stairs.
• To determine the energy burned during that exercise
Theory
In this lab you will examine three physical quantities: Energy, Work, and Power and
related units of measure.
One of the most important concepts in science is energy. Our universe is made of matter
and energy. Matter is substance and energy moves the substance. The concept of matter is
easy to comprehend, because we can see, feel, smell, or measure it. Energy, on the other
hand is very abstract concept, we can’t see, feel, or smell it. But fortunately we can
measure it. There are a number of units used to measure energy. A non metric unit of
calorie (cal) is one of them.
The energy equal to 1 calorie is defined as the amount of heat required to raise the
temperature of one gram of water from 14.5oC to 15.5oC.
When we work with nutritional values and food, a unit of Calories (Cal – capitol C) is
used. Relation between cal and Cal is:
1 Cal = 1000 cal
Metric unit for energy is Joule (J). The energy of 1 Joule is equal to amount of heat
needed to rise the temperature of 1 g of water for 1 oC. The relation between the three
mentioned units is:
1 kcal = 1000 cal
1 cal = 4.19 J
1 Cal = 4190 J
When we lift the load against the earth’s gravity, work is done on the load. The more
mass on the load or the higher we lift the load, the more work is done. Every time when
force is applied and something has moved because of that force. Work is defined a as
product of force and distance.
W=Fd
If we lift 20 kg one story up, we perform twice as much work compared to lifting only 10
kg load, because twice as much force is needed to lift 20 kg. The unit of measurement of
work is combination of unit of force N and unit of distance m: Nm which is also called
Joule J. When work is done on an object, the energy of object is changed – object can
then perform work. When work is done on metal spring mechanism, the spring acquires
the ability to do work on various gears to run the clock, to ring the bell, etc. Work can be
done at various rates, or energy can be changed at various rates. In some situations
happens faster in some others it happened slower. You can walk up stairs or you can run
upstairs in one floor. In both cases you are doing same work but at different rates. The
rate at which the energy is changed, or work is done is called Power “P”.
P = work done/ time interval
The unit of power is:
Joule/second = Watt
J/s = W
Procedure (Intro Exercise)
1. Choose an exercise that involves doing work (such as lifting an object, raising on
toes, sit-ups, push-ups, etc.).
2. Perform this exercise slowly, and:
o Measure or estimate the force that you exert during the exercise. (Hint: At
the surface of the earth, 1 pound = 4.45 Newtons (approximately))
o Have your lab partners help you measure the distance that you exerted the
force.
o Enter your measurements in a data table.
3. Now, perform several repetitions of the exercise as fast as you can (while being
safe!). Have your lab partners count the repetitions and measure the total time it
takes.
4. Repeat for some other exercise. If your first exercise involved your arm muscles,
pick another exercise that involves your legs, or vice versa.
Calculations: (Show work here)

The work required to perform your exercise = the force you exerted times the
distance you exerted it.

The total work you did = the work for one repetition times the number of
repetitions that you performed.

Your power output = the total work you did divided by the total time taken.
Data Table
Force exerted (N)
Distance exerted
(m)
Time it takes to do
10 repetitions (s)
Work for one
repetition (J)
Total Work (J)
Power Output
(Watts)
Analysis:
1. How does the power output of your arm muscles compare to the power output of
your leg muscles? Why do you think this is?
2. How does your power output compare to the power output of a 60 Watt light
bulb? A small lawnmower engine (1 horsepower = 746 Watts, approximately)?
3. Is the power output of your muscles more or less than you thought it would be?
(For Part I) – Determine the power done and energy burned by walking up stairway for
one floor:
1. Each group of students should consist of two students: student A, and student B.
Both students will perform the experiment in the stairway at the end of the
hallway, toward the exit way.
a. Both students measure their mass in kilograms and calculate their weight –
force in Newton’s.
b. If the mass is measured in pound – change that into kilograms.
c. Record the mass and the weight of each student in table.
2. After these measurements, students will measure the vertical height of the stairs.
a. They should measure the height of one step and then multiply by the
number of steps in the stairs. The height should be converted into meters
and recorded in table.
3. Student A starts walking upstairs and student B should measure the time required
to walk up to second floor. Time should be recorded in seconds.
4. Student B starts walking upstairs and student A should measure the time required
to walk up to second floor. Time should be recorded in seconds.
5. Each student should walk up stairways 4 times and record the average time.
(For Part II)– Determine the power done and energy burned by running up stairway one
floor:
Repeat steps from part I by running up stair way one floor.
Data Table
Analysis/Questions
1. Is there a difference in power done walking and power done running upstairs and why?
2. Two guys lift two 40 N rocks up a 5 m staircase. Bob does it in 10 seconds.
Joe does it in 20 seconds. Compare their work and power.
3. If a student had a single peanut before this lab, how many times would a student have
to run upstairs in order to burn the energy from a single peanut? A single peanut has the
energy of 5 Calories = 5000 cal = 20.95 kJ.
4. When doing a chin-up, a physics student lifts her 42.0-kg body a distance of 0.25
meters in 2 seconds. What is the power delivered by the student's biceps?
5. Your household's monthly electric bill is often expressed in kilowatt-hours. One
kilowatt-hour is the amount of energy delivered by the flow of l kilowatt of electricity
for one hour. Use conversion factors to show how many joules of energy you get when
you buy 1 kilowatt-hour of electricity.
6. An escalator is used to move 20 passengers every minute from the first floor of a
department store to the second. The second floor is located 5.20 meters above the first
floor. The average passenger's mass is 54.9 kg. Determine the power requirement of the
escalator in order to move this number of passengers in this amount of time.