Name
___________
_
____________
_________________________________________________
You have the
Power
Introduction
The word work represents a concept that has a special meaning in science that is somewhat different from your everyday concept of the term. In science, the concept of work is concerned with the application of a force to an object and the distance the object moves as a result of the force. Work
(W) is defined as the magnitude of the applied force (F) multiplied by the distance (d) through which the force acts, W = Fd.
mgd=
P t
d
F = mg
Figure 13.1
You are doing work when you walk up a stairway since you are lifting yourself through a distance. You are lifting your weight (the force exerted) the vertical height of the stairs (distance through which the force is exerted).
Running
up the stairs rather than walking is more tiring because you use up your energy at a greater rate when running. The rate at which energy is transformed or the rate at which work is done is called power. Power (P) is defined as work (W) per unit of time (t),
P = W
t
When the steam engine was first invented there was a need to describe the rate at which the engine could do 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 engine, defined
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125
horsepower (hp) as a power rating of 550 ft·lb/s. In SI units, power is measured in joules per second, called the watt (W). It takes 746 W to equal 1 hp, and 1 kW is equal to about 1.33 hp.
Today let us calculate how much work you must do to “burn” Calories consumed. For example, a Peanut Butter Cup (pack of two and from the label) has 240 Calories per serving. My alltime favorite candy!
The following information will be needed in this activity for question 6.
Thermal calories are represented by “calorie” with a lower case “c”. The abbreviation is “cal”
Nutritional or dietary Calories are represented by “Calorie” with an upper case “C”. The abbreviation is Cal.
1000 calories = 1 Calorie
4.184 Joule = 1 calorie
We want to answer the question using the energy unit, Joule. For a peanut butter cup which has 240 Calories per serving, we can convert to Joules by the following calculations:
240 Calories = _________ Joules
240 Calories (1000 calories / 1 Calorie) = 240,000 calories
240,000 calories (4.184 J/ 1 calorie) =
1.004 x 106 J
Now let’s find out how much work you must do to “burn” off your favorite snack food Calories.
Procedure (SHOW ALL WORK!)
1. You, the Blue Raider, and another volunteer will measure the work done, the rate at which work is done, and the horsepower rating as you move up a stairwell. The volunteer will measure and record the data for you. First, write down the weight of the Blue Raider. measure and record the data for person A. An ordinary bathroom scale can be used to measure your weight. Record the weight in pounds (lb.) in
Data Table
. This weight is the force (F) needed by you to lift yourself up the stairs.
Your weight in pounds = _____________________________
Your weight in kilograms = __________________________
Assume that the acceleration due to gravity is implied. In other words, you do not need to calculate weight (w = mg) for this experiment. Assume that your weight is the force!
Also, you might need the following conversion: 1 kg = 2.20 pounds
2. 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 this distance (d) in feet (ft) in Data Table.
Height of one step = ____________________ Number of steps = __________________________
Distance traveled in feet = _____________________________________
Distance traveled in meters = __________________________________
Recall that 1 m = 3.281 ft
3. Measure and record the time required for you to
walk normally (and carefully!)
up the flight of stairs. Your volunteer can do this on a cell phone. Record the time in seconds
(s)
in Data Table.
Time (walking) = ______________________
4. Measure and record the time required for you to
run carefully
up the flight of stairs as fast as can be safely accomplished. Record the time in seconds (s) in Data Table.
Time (running) = ______________________________________
5. 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 results in Data Table.
Work = Fd (walking) _______________________________ Joules “burned” doing work
Work = Fd (running) _______________________________ Joules “burned” doing work
Power = Work / time (walking) = ___________________________________
Power = Work /time (running) = _____________________________________
You can find a conversion for horsepower in your textbook.
Horsepower (walking) = __________________________________________
Horsepower (running) = __________________________________________
6. Read the label on your favorite snack food. Use a different snack. Don’t forget units. Complete the following:
· Name of favorite snack = _________________________
· Calories per serving = ___________________
· Servings per snack = ___________________
· Total Calories per snack = ________________
· Convert the Total Calories to thermal calories. Show all work.
· Convert thermal calories to Joules. Show all work. This value is Joules Gained.
7. Compare your Joules gained (from the snack) to Joules burned (from the exercise). Which is larger? What does this tell you about food and exercise?
Results
1. Explain why there is a difference in the horsepower developed(but not in work) in walking and running up the flight of stairs. Use your data.
2. Work has the same units as energy. What does this tell you? Use your data. Explain your answer.
3. What did you learn from this activity? Use correct grammar, spelling and complete sentences.
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126
Data Table You have the Power 

Walking 
Running 
Weight (F) (kg) 

Vertical height (d) of steps (m) 

Time required (t) to walk the flight of steps (s) 

Time required
(t) to run the flight of steps (s) 

Joules Burned (Work done) W = Fd (J) 

Power
P = W/t (J/s) 

Horsepower developed P ÷ 550 ft·lb/s 

Joules Gained from snack (J) 
____________
____________
____________
___________
____________
____________
___________
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128
Data is provided. Read and follow the directions carefully!
Introduction
An estimate of pi was made by the ancient Chinese and Egyptians who used a value of 3. But the Greeks were probably the first to make a more accurate determination. Archimedes found the value of
pi as a number between 31/ 7 and 310 / 71• A more accurate value was not possible until the decimal system was introduced in the 17th century. Today modern computers can determine pi with more than a mil lion digits after the decimal.
In today’s experiment we shall determine the value of pi by examining the relationship between the radius of a circle and its circumference.
The direct proportionality between any two entities, y and x, is represented by the generic equation of a straight line:
y=mx+b
in which m and bare constants. The value of mis called the slope of the line. The value of bis called theyintercept because it becomes the value of y when x = 0.
If we assign the symbols c for circumference and
d
for diameter, the equation can be written as
c = md + b
In this equation the slope, m, of the line shows the direct relationship between circumference and diameter, which is the value of 7t.
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10 Experiments in Physical Science
Equipment
Several circular objects (Assortment of PVC pipes) Ruler, 30 cm
Procedure
I. Measurements. Obtain a variety of circular objects from the instructor’s desk. (Return them to the desk when you have finished using them.) Measure the diameter, d, and the circumference, c, of six circular objects. Make sure that you are measuring the outer diameter. Include the largest and smallest object. You will find it easier to use the decimal scale. Your measurements should be pre cise to a tenth of a centimeter (or millimeter). Record your measurements in the Data Table on the lab report. Pay attention to significant figures. If your measurement happens to fall exactly at the centimeter level, then you need to show that there are no millimeters beyond that point and you place a decimal point followed by a zero. For example, if your measurement happens to be exactly 12 cm and nothing more (or less) than 12, you would report 12.0 cm.
Note: In a data table, if units are given at the head of a column, you should not repeat them after each number in the column.
2. Plotting. You will now determine the pattern that exists between diameter and circumference by graphing the data that you have obtained. Using the graph paper provided, the horizontal (x) axis will represent the diameter, d, and the vertical (y) axis, the circumference, c. For each measured circular object, plot the value corresponding to its diameter and circumference as a single point surrounded by a small circle on the graph (0). Use a ruler and a lead pencil to draw the best straight line through all the points. The “best straight line”, also called the trendline, is a single line that passes through, or as close to, as many points as possible. This line represents an average trend for all the points, although it may not pass through any point.
3. Slope of the line. You will now determine the slope, m, of the line on your graph. Locate any two points on the line, fairly wide apart, and find their values, cl’ d1 and cz, dz.
The points should be taken from the line on your graph and not from any of the measurements. Mark each point with
an arrow, but do not draw a circle around the points because they are not actual measurements.
On your data sheet, calculate the ratio (cz – c1) I (dz – d1 ) . This is the slope of the line, which is your experimental value of 7t.
4. Theyintercept. Use a ruler to extrapolate (extend) the line all the way to the vertical axis. The point where the line meets the vertical axis gives the value of the constant, b, called the yintercept. The value of b obtained from your graph can be positive if the line meets they axis above zero, negative if it meets they axis below zero, or zero if it exactly meets the origin.
Now consider this: As the circumference of a circle gets smaller, what happens to the diameter? It gets smaller too, of course. This means that as c approaches zero, so does the value (md + b) and therefore the value of b will also be zero. Theoretically therefore, the equation of your line should be:
c= md+ 0 or c = md
Determining the Value of Pi 11
5. The percent error is a measure of how close your results are to an accepted value. It is determined as follows. Note that only the absolute value of a difference is used. Calculate your percent error for pi.
6. Note that the accepted value of pi = 3.14
15
9
7. Calculate your percent error using the following equation.
Percent error = Accepted value – experimental value x 100
Accepted value
= ___________%
NAME PARTN ER. .SECTIO N _
Data and Results for Determining the Value of Pi
DATA TABLE
Description of Measured Object
Diameter (cm)
Circumference (cm)
Small pipe
3.7
13
.0
Small to medium pipe
4.5
16.1
Medium pipe
5.3
18.0
Large Pipe
9.7
32.0
Extra Large pipe
11.1
34.9
2XL Pipe
14.2
40.0
1. Use a lead pencil to plot the data in the table on the graph paper provided, and use a ruler to draw a bestfit line through your data.
2. Locate two convenient points on your line, and determine the slope, m, of the line on your graph.
Show your work:
This is your experimental value of pi. Give its value to three significant figures
3. Give the value of theyintercept, b, obtained from your graph cm Theoretically, what should this value be? cm
Is your value reasonably close to what it should be theoretically? [Yes] [No] (Circle the correct answer.)
13
14 Experiments in Physical Science
4. Now you can use the values that you obtained for your slope and yintercept to complete the equation of your straight line:
c= d+ _
5. Calculate the percent error from the actual value of 7t. (See page 11 .) Show your work:
Sources of Error
1. While determining the circumference of a cylindrical object, suppose that you wrapped the measuring tape around it at a slight slant. Comment, using complete sentences, on how this would affect the following:
a. Would your circumference measurement be larger, smaller, or would it make any difference?
b. Would the value you obtain for pi be larger, smaller, or would it make any difference?
2. While measuring the diameter of a circular object, suppose that your ruler did not pass exactly through the center of the circle. Comment on how this would affect the following:
a. Would your diameter measurement be larger, smaller, or would it make any difference?
b. Would the value you obtain for pi be larger, smaller, or would it make any difference?
3. In determining the slope of your line, why is it more precise to select points on the line and not from any of the measurements?
15.0
15
Eventhough you are conducting these labs at home, we do want you to be aware of laboratory safety.
For this lab activity, read and answer questions in the following sections:
Read Laboratory Safety Rules and answer questions on lab report Part A: Laboratory Safety
Do not answer B, Laboratory Safety and
Equipment
Answer the questions for C.
Measuring Length
Complete D.
Measuring the Density of a Solid: Pennies
. Complete Data Table 1 and SHOW ALL WORK!
Introduction
In this introduction to the physical science laboratory, you will become acquainted with safety rules and equipment, perform a measurement of length, an experiment using density and significant figures, and use a pendulum with timer to find what determines its period.
Laboratory Safety Rules
Safety is a very important issue in any laboratory. All students are required to follow the laboratory rules listed. Violation of the rules may result in a student being removed from the laboratory for the one lab period. Continual violation of the rules will be grounds for action aimed at removing the vio lator from the laboratory on a permanent basis
1. Approved safety goggles are required to be worn at all times for experiments involving chemicals. Persons with contact lenses are encouraged to wear glasses to the lab, if possible. Students wearing eyeglasses or contacts must wear safety goggles also. Approved safety goggles are available at Phillips Bookstore.
2. Eating and drinking in the laboratory are absolutely forbidden. Any food or beverage brought into the laboratory will be considered contaminated and will be disposed of immediately.
3. Backpacks, purses, books, and jackets may not be placed on or around a lab bench, or on the floor. They can cause spills or present a tripping hazard. All belongings must be stored in an area designated by the lab instructor.
4. No horseplay, roughhousing, or any other form of physical activity not directly required for the experiments will be tolerated in the laboratory.
5
. Students must have supervision while in the lab. Students are not permitted in the laboratory without a lab instructor present.
6. No unauthorized experiments of any kind will be performed by any student.
7
. No opentoed shoes, flipflops, or sandals are to be worn in the laboratory.
8. Shorts, skirts, and dresses must be kneelength or longer. All students are reminded that chemicals have a tendency to spill and stain clothes. Students are encouraged to wear old clothes to the lab.
9. No exposed midriffs (stomach area) will be permitted.
10. Long hair (shoulder length or longer) should be tied back so that it does not hang over open flames or in the student’s face. This rule applies to both genders.
11. Know the location of all safety equipment, including exits, safety showers and eyewashes, fire extinguishers, and fire alarms.
12. All accidents involving personal injury, no matter how minor, must be reported to the teaching
assistant, supervisor, or to the instructor immediately.
13. Wash skin thoroughly in the event of contact with hazardous chemicals. All accidents involving spilled chemicals or broken glass, no matter how minor, must be reported to the teaching
assistant, supervisor, or to the instructor immediately.
14. The laboratory work area must be kept clean at all times.
Laboratory Equipment
Common laboratory equipment is illustrated on page vii of your laboratory manual. You will locate these items on the cart in the laboratory and draw a sketch of the equipment listed on your data sheet.
Measuring Length
You will draw a line 12.7 cm long on your report sheet and answer questions about its length.
Measuring the Density of a Solid: Pennies
In this experiment, you will determine the density of United States pennies. Pennies are made of cop per, but are they pure copper? You will compare the density value you obtain for pennies to the known density value of copper, which is 8.96 g/mL.
To determine if the pennies are pure copper (using density), you will need to determine both the mass
and volume of the pennies, given the density equation:
Density = mass/ volume (units of g/mL, or kg/L))
Equipment
Pennies (minted after 1983) 50 mL graduated cylinder Top loader balance
Data is provided for you in Data Table 1.
Procedure
You will use the electronic balance at your desk. Lift the lid open and press the ON/OFF button. After a few seconds the screen will read “0.00 g”. If it does not, press the ZERO button to TARE the balance before weighing.
1. Count out 20 pennies and weigh them together on the balance. If the pennies are wet, dry them first with a paper towel.
2. Record the mass of the pennies to the nearest 0.01 g on the data table. You now have the mass
component of the density equation.
3. Determine the volume of the pennies using a method of “water displacement.” Add between 20 and 30 mL water to a graduated cylinder. Record this initial volume to the nearest 0.1 mL on your data sheet. You will need to estimate between the lines on your graduated cylinder. Ask your instructor if you need help.
4. Carefully place all 20 pennies into the water in the graduated cylinder. The water level will rise, or be displaced, by an amount equal to the volume of the pennies. Read and record the new, or final volume, to the nearest 0.1 mL. The difference between the final and initial water volumes is equal to the volume the pennies occupy. Calculate this volume on the data sheet.
5. Calculate the density of the pennies on your data sheet. Make sure that you use the correct sig nificant figures in your calculation. (See page ix)
6. Perform a second trial by repeating steps 1 to 4. Use a different initial volume of water.
7. Calculate the average of both density trials, and be sure to use correct significant figures.
NAME. PARTNER, SECTION _
Data and Results for Safety and Measurement
A. Laboratory Safety
1. Why must goggles be worn at all times in the chemistry laboratory? Please use complete sentences throughout your work.
2. Where should backpacks, purses, books, jackets, etc. be placed in the laboratory? Why can they not be at or around your bench?
3. What should you do in case of a chemical spill or injury that occurs while in the lab?
4. What types of shoes and clothing are not permitted to be worn in the lab?
5. Why are food and drink not allowed in the laboratory?
5
6 Experiments in Physical Science
B. Laboratory Safety and Equipment = DO NOT DO THIS SECTION
1. In the table below, give the location of five safety features found in this laboratory.
Safety Feature 
Location 
2. Draw the following items in the space below.
a. Erlenmeyer flask b. Graduated cylinder c. Pasteur pipette
C. Measuring Length Do this section.
In the space below, use a small ruler to draw a straight line measuring 12.7 cm.
What is its length in millimeters? (always include units.) _ In meters? _
In kilometers?
NAME PARTNER. SECTION _
D. Measuring the Density of a Solid: Pennies
DATA TABLE I
Trial I
Trial 2
Mass of pennies using balance
50.03 g
50.18 g
Density = volume =
mass
Average both density calculations (show your work):
Average penny density: _
Initial volume of water in cylinder 
50.0 ml 
58.3 ml 
Final volume of water plus pennies 
57.0 ml 
65.1 ml 
Volume of pennies (Final – Initial) 
7.0 ml 
6.8 ml 
Density of pennies: (show your work below) 
g/ml 
g/ml 
3. The density of pure copper is 8.96 g/mL. Are U.S. pennies made of pure copper? Explain your answer.
7