Physics Laboratory Experiments 8e Instructor’s Manual 1
SOLUTIONS MANUAL
,2 Physics Laboratory Experiments 8e Instructor’s Manual
EXPERIMENT 1. THE SCIENTIFIC METHOD AND THOUGHT
Skewed Balloon (And it doesn't burst)
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible
website, in whole or in part.
, Physics Laboratory Experiments 8e Instructor’s Manual 3
The purpose of the demonstration is to get the students to think and apply the
scientific method (or scientific thinking) in forming explanations and drawing
conclusions. The demonstration consists of pushing a wooden (bamboo) skewer
completely through an inflated balloon without it collapsing (• Fig D1).
Items needed
• Latex rubber balloons (12-in. size)
• Bamboo skewers (12-in. long, found in the grilling or cooking section)
• Cooking oil (small amount)
Procedure
1. Blow up balloon to nearly full size and let air out so about 2/3 in size
(about 9 inches). Tie a knot in the end to keep the balloon inflated. Note
the thick areas of the inflated balloon near the tied knot and opposite end.
2. Fully rub cooking oil on the length of the skewer with the fingers. (You can
do this openly or surreptitiously, depending on how difficult you want to
make the demo explanation.)
3. Place the sharp end of the skewer on the thick end of the balloon near the tie
aiming toward the opposite thick end. Use gentle pressure (twisting may
help) and puncture the balloon.
4. Push the skewer steadily toward the opposite end until the tip of the skewer
touches the thick end portion of the balloon. Keep pushing until the skewer
tip penetrates through the rubber a couple inches. The skewed balloon
should remain inflated. (A little air may be lost.)
5. Ask the students to explain. You may want to repeat the demonstration
showing the oil coating of the skewer if you didn’t do it before.
, 4 Physics Laboratory Experiments 8e Instructor’s Manual
Explanation
Latex rubber is made up of long-chain polymer molecules. When the balloon is
punctured, the long chains form a seal around the skewer. The cooking oil acts as a
lubricant for the puncture.
EXPERIEMENT 2. EXPERIMENTAL UNCERTAINTY (ERROR)
AND DATA ANALYSIS
Problem in Data Analysis (There's something missing)
Procedure
To illustrate a problem in data analysis, have the students consider the following:
A student wants to buy a new cell phone for $97 and borrows $50 from each of
two friends. He buys the phone and gets $3 back. He gives each friend $1 and
keeps the other $1.
Now he owes his two friends $49 apiece. But $49 plus $49 is $98; and when you
add the $1 he kept, you get $99. Where is the missing dollar?
Explanation.
The data was manipulated and the wrong figures added. The student now has a $97
cell phone plus $1 cash. That totals $98, which indeed is what he owes to his
friends.
EXPERIMENT 3. MEASUREMENT INSTRUMENTS (MASS,
VOLUME, AND DENSITY)
Mixed Liquids Become More Dense
The purpose of this demonstration is to show the students how unexpected results
may occur in an experiment from unexpected sources. 500 mL of methyl alcohol
(ρal = 0.790 g/cm3) and 500 mL of water (ρw = 1.000 g/cm3) are weighed (in grams),
from which the density of a mixture may be theoretically determined. The liquids
are mixed, and the mixture’s weight and volume measured. Using experimental
measurements, the density of the mixture is calculated and found to be greater than
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible
website, in whole or in part.
SOLUTIONS MANUAL
,2 Physics Laboratory Experiments 8e Instructor’s Manual
EXPERIMENT 1. THE SCIENTIFIC METHOD AND THOUGHT
Skewed Balloon (And it doesn't burst)
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible
website, in whole or in part.
, Physics Laboratory Experiments 8e Instructor’s Manual 3
The purpose of the demonstration is to get the students to think and apply the
scientific method (or scientific thinking) in forming explanations and drawing
conclusions. The demonstration consists of pushing a wooden (bamboo) skewer
completely through an inflated balloon without it collapsing (• Fig D1).
Items needed
• Latex rubber balloons (12-in. size)
• Bamboo skewers (12-in. long, found in the grilling or cooking section)
• Cooking oil (small amount)
Procedure
1. Blow up balloon to nearly full size and let air out so about 2/3 in size
(about 9 inches). Tie a knot in the end to keep the balloon inflated. Note
the thick areas of the inflated balloon near the tied knot and opposite end.
2. Fully rub cooking oil on the length of the skewer with the fingers. (You can
do this openly or surreptitiously, depending on how difficult you want to
make the demo explanation.)
3. Place the sharp end of the skewer on the thick end of the balloon near the tie
aiming toward the opposite thick end. Use gentle pressure (twisting may
help) and puncture the balloon.
4. Push the skewer steadily toward the opposite end until the tip of the skewer
touches the thick end portion of the balloon. Keep pushing until the skewer
tip penetrates through the rubber a couple inches. The skewed balloon
should remain inflated. (A little air may be lost.)
5. Ask the students to explain. You may want to repeat the demonstration
showing the oil coating of the skewer if you didn’t do it before.
, 4 Physics Laboratory Experiments 8e Instructor’s Manual
Explanation
Latex rubber is made up of long-chain polymer molecules. When the balloon is
punctured, the long chains form a seal around the skewer. The cooking oil acts as a
lubricant for the puncture.
EXPERIEMENT 2. EXPERIMENTAL UNCERTAINTY (ERROR)
AND DATA ANALYSIS
Problem in Data Analysis (There's something missing)
Procedure
To illustrate a problem in data analysis, have the students consider the following:
A student wants to buy a new cell phone for $97 and borrows $50 from each of
two friends. He buys the phone and gets $3 back. He gives each friend $1 and
keeps the other $1.
Now he owes his two friends $49 apiece. But $49 plus $49 is $98; and when you
add the $1 he kept, you get $99. Where is the missing dollar?
Explanation.
The data was manipulated and the wrong figures added. The student now has a $97
cell phone plus $1 cash. That totals $98, which indeed is what he owes to his
friends.
EXPERIMENT 3. MEASUREMENT INSTRUMENTS (MASS,
VOLUME, AND DENSITY)
Mixed Liquids Become More Dense
The purpose of this demonstration is to show the students how unexpected results
may occur in an experiment from unexpected sources. 500 mL of methyl alcohol
(ρal = 0.790 g/cm3) and 500 mL of water (ρw = 1.000 g/cm3) are weighed (in grams),
from which the density of a mixture may be theoretically determined. The liquids
are mixed, and the mixture’s weight and volume measured. Using experimental
measurements, the density of the mixture is calculated and found to be greater than
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible
website, in whole or in part.
