1
EDSE 460
Michael Dzwiniel
20 January 2005
Assignment #1
Gravitational Acceleration (g) Lab
W. Steven Schneider
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Presentation for Gravitational Acceleration (g) Lab
Purpose:
•
•
Educational – demonstrate how physicists test a law
Scientific – test the validity of Fg = mg, where g is the acceleration due to gravity
Overview:
This is a lab typically preformed in a grade seven science course and it allows the student
the opportunity to falsify Newton's Second Law of Motion. The idea here is that the
student comes to realize that theories and physical laws have to be supported by empirical
evidence, and that separate observers can agree that it is the same.
– students are given a prediction of earth's gravitational acceleration
– students collect the evidence in the lab
– students calculate earths gravitational acceleration from their collected evidence
– students determine if the results are valid for this lab through error analysis, and
proximity of determined answer to predicted value
Lesson Introduction:
1. get classes attention
2. “We're going to do the Gravitation Acceleration Lab today...”
• “Do any of you remember Newton's Second Law of Motion?”
g
• “How can we relate this to gravity?” Fg =m 
 =m a
F
Lesson Closure:
1. Would the results be similar if we did this experiment in another country?
2. Can Newton's Second Law tell us anything about how masses would fall near the
surface of Mars? How would you test it?
Closure for Classmates:
As you can see, this lab lets the student test the validity of Newton's Second Law of
Motion. This may, in turn, encourage the student to test out other concepts that are often
passed as “physical laws.” I attempt to reinforce this through a set of post lab questions,
and as a sub-theme throughout most of the course.
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Information for Teacher for Gravitational Acceleration (g) Lab
One educational concept that I will be attempting to use is the idea of brain growth. How
do I help their brains make permanent connections regarding the scientific principle that I
am attempting to teach? What kind of things can I do in this lesson that will increase the
chances of them recalling it? Can I find any “Real World” examples that could be related
to what they are learning today?
To do so, some of the following educational strategies I will attempt to use in this lesson
are directed learning, lecture, independent learning, and, of course, lab work.
When they come out of this lesson it is hoped that the students will have the correct idea
of Testing in their brains. Afterwards, it will simply be a matter of reinforcing it in
lectures, homework (such as reading, or questions), and as a sub-theme in other labs, and
lessons throughout the course.
The following are the pre-lab questions which I am using to get the students to think
about the math involved in the physical law that we are testing. I remind the students that
we are using SI units so conversion may be necessary, and always remember their
Significant Digits.
Given a 50 g mass, calculate Fg if g = 9.81 m/s2. Fg =
Given the same mass, calculate Fg if g = 10 m/s2. Fg =
N
N
A 25 g mass experiences a force of 0.25 N, what is the acceleration of the mass?
g=
m/s2
A 100 g mass experiences a force of 0.981 N, what is the acceleration of the mass?
g=
m/s2
In my post lab questions I am attempting to get the students to think about some of the
implications of the lab, and how they could test them. Again there are reminders to use
SI units, and Significant Digits.
1. If we repeated this experiment in Australia, could you expect the results to be similar,
or different? How about in Russia, or Nigeria?
2. The value we found was obtained close to the earth's surface. Do you think the result
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might have been different if we were up on a mountain? How about in an airplane, or
in orbit aboard the space shuttle?
3. Can Newton's Second Law tell us anything about the acceleration due to gravity of the
Moon? How would you test it?
4. Assuming that you could survive, how about on the surface of the Sun?
5. There are cases, such as buoyancy, which seem to defy the claim that earth's gravity
pulls things to its surface. Based on what you have learned in this lab, can you think
of a reasonable explanation of why this appears to be the case, and how you might test
it?
Ideally, to preform this lab with a class of thirty students the teacher will require the
following materials:
• fifteen metal stands
• fifteen metal clamps
• fifteen spring force scales
• fifteen 25 g masses
• fifteen 50 g masses
• fifteen 100 g masses
Fasten one metal clamp to the top of each metal stand. Then hang one force scale to each
clamp. Instruct the student groups to only use the 25 g mass if their group has a scale
which cannot be set to zero AND the scale indicator is off of the graduated section.
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Sample Report:
Problem:
What is the acceleration due to gravity (g) experienced by masses having the values of 50
g, 100 g and 150 g?
Prediction:
According to Newton's Second Law, when an object of mass (m) is experiencing an
acceleration – a change in speed, or direction - (a), then there is a force (F) acting on it.
On earth we notice that some force acts on objects “forcing” them toward its surface.
This force is known as the force of gravity (Fg), and the acceleration is known as the
acceleration due to gravity (g).
Physicists have measured this acceleration (g) and have so far determined it to be
approximately 9.81 m/s2.
In this lab, we will find the acceleration due to gravity (g) that a set of known masses
experience due to the force of gravity (Fg), and determine whether or not Newton's
Second Law is valid. If it is, we should get a value close to 9.81 m/s2.
Remember, we are NOT trying to get the “right” answer, we are trying to see for
ourselves if Newton's Second Law deserves to be a law.
Newton's Second Law:
 =m 
F
a

F g =m g (g: acceleration due to gravity = a: acceleration)
To find acceleration due to gravity: g =
Fg
m
Experimental Design:
Known masses will be measured on spring scales. The force of gravity (Fg ) will be
determined from the difference between the initial (beginning) and final readings of
force on the spring scale. This value will then be used to see if the acceleration due to
gravity (g) can be found.
Your set of masses includes a 25 g mass, this mass will NOT be used to calculate
acceleration. Some of the scales cannot be set to zero, and have initial readings which are
off of the scale. If your scale has an initial reading which is off of the scale then use the
25 g mass to bring the indicator down into range, and use that as your initial force.
In the initial force column of the the table below, record the beginning position of the
indicator on the scale to the nearest decimal place of a Newton. Add the 50 g mass and
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record its final position in the final force column of the table below. Find the force of
gravity by subtracting the initial force from the final force such that:
Fg = final force−initial force
and record the result in the Fg column in the following table.
Evidence:
mass
(kg)
final force
(N)
Analysis: (show calculations)
initial force
acceleration
Fg
(N)
(m/s2)
(N)
0.050
0.7
0.2
0.5
1 x 101
0.100
1.2
0.2
1.0
10
0.150
1.7
0.2
1.5
10
Materials:
one metal stand
one metal clamp
one 2.5 N spring scale
one 25 g mass
one 50 g mass
one 100 g mass
Conversion: 3/3
SD's:
15/15
Calculation: 6/6
Total:
24/24
Pre-Lab Questions:
(Give all answers in appropriate SI units so convert as necessary. Remember your
significant digits. Mass (m) is in kilograms when using SI units.)
Given a 50 g mass, calculate Fg if g = 9.81 m/s2. Fg = 0.49 N
3/3
Given the same mass, calculate Fg if g = 10 m/s2. Fg = 0.50 N
3/3
A 25 g mass experiences a force of 0.25 N, what is the acceleration of the mass?
g = 10
m/s2
3/3
A 100 g mass experiences a force of 0.981 N, what is the acceleration of the mass?
g = 9.81 m/s2
3/3
36/36
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Analysis:(Record results in table. Remember Significant Digits.)
Convert grams to kilograms:
50 g = 0.050
kg
100 g = 0.100 kg
6/6
150 g = 0.150 kg
Determining force of gravity:
Fg = final force−intial force
0.7 N – 0.2 N= 0.5 N
1.2 N – 0.2 N = 1.0 N
1.7 N – 0.2 N = 1.5 N
6/6
Calculations of acceleration due to gravity: g =
0.5 N/0.050 kg = 10 m/s2
1.0 N/0.100 kg = 10 m/s2
1.5 N/0.150 kg = 10 m/s2
Fg
m
6/6
Calculate the percent difference: diff =
 g −9.81 m/ s 2 
×100
9.81 m/ s 2 
((10 m/s2 – 9.81 m/s2)/9.81 m/s2) x 100 ~ 2 %
2/2
20/20
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Evaluation:
Based on percent difference was Newton's Second Law verified, or falsified?
If a law is verified when its %diff <= 5% then Newton's Law has been verified in this
instance.
1/1
Error of scale: ±0.05 N
Error of masses: ±0.5 g
(0.05 g / 50 g) x 100 = 0.1 %
(0.05 g / 100 g) x 100 = 0.05 %
(0.05 g / 150 g) x 100 = 0.03 %
6/6
Total error:
2 % + 0.1 % ~ 2.1 %
2/2
What does the total error say about the experiment?
The size of the total error tells us that the results of the lab are reasonably accurate
despite any errors due to the instrumentation, and can be accepted with a high degree of
confidence.
1/1
How good a test of acceleration due to gravity do you think the experiment was?
1/1
How easy did you find the procedure to follow?
1/1
12/12
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Synthesis:
1. If we repeated this experiment in Australia, could you expect the results to be similar,
or different? How about in Russia, or Nigeria?
You can expect the results to be similar in all of the above cases.
1/1
2. The value we found was obtained close to the earth's surface. Do you think the result
might have been different if we were up on a mountain? How about in an airplane, or
in orbit aboard the space shuttle?
Gravity's effects drop off as one leaves the surface of the Earth. With sensitive enough
equipment one should see these differences grow the higher one goes.
2/2
3. Can Newton's Second Law tell us anything about the acceleration due to gravity of the
Moon? How would you test it?
If laws are uniform throughout the universe, and Newton's Second Law works on Earth,
then is should work on the surface of the Moon too. You could preform the same
experiment we did today, or another experiment that is used for finding acceleration due
to gravity.
2/2
4. Assuming that you could survive, how about on the surface of the Sun?
(Similar to above.)
2/2
7/7
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5. If you performed this lab, but kept getting a result of 20 N, you did not make any
mistakes during the lab, and your equipment was working properly, what could you
say about Newton's Second Law?
Newton's Second Law is no longer valid.
1/1
Fg =2 m g is the resulting new equation for force due to gravity.
6. What would have to happen before scientists would accept what your evidence says
about Newton's Second Law?
They would have to try to disprove it by testing it in a wide variety of locations on Earth's
Surface.
1/1
7. There are cases, such as buoyancy, which seem to defy the claim that earth's gravity
pulls things to its surface. Based on what you have learned in this lab, can you think
of a reasonable explanation of why this appears to be the case, and how you might test
it?
(This question is a little open ended. We're looking for critical thinking skills,
application of Newton's Second Law, and a some imagination.)
Bonus: 3/3
5/5
Total: 80/77
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Lesson Plan for Gravitational Acceleration (g) Lab
Objectives:
Teacher will teach the Nature of Science principle of testing through this lab.
Students will learn the Nature of Science principle of Testing.
• Students will be able to test a law, or a point of theory with reasonable skill to
determine its validity.
• Students will learn to find evidence to support, or refute, accepted “fact”
Motivation:
- Demo
– hold two different masses (baseball and softball stolen from Phys. Ed. Dept.?) and ask
which would fall faster? Tell them to write their answers down on a piece of paper
and that I'll ask someone to give it after a minute.
– After student give answer ask how many agree, and disagree
– drop both masses at same time, repeat if necessary and discuss results
Lesson/Lab:
- review highlights on Newton's Second Law of Motion
• ask if any student needs further clarification
• ask students if they did their “Pre-lab” worksheets
• pass out procedures, and post-lab questions
- model how to “do” the lab
• when to use 25 g mass
• how to hang masses on scale
• how to record values on table (slide show, overhead)
- let students preform the experiment
• make sure every student is part of a group
• make sure every student has everything that they need to do the lab
• walk around to see how they're doing
• answer questions
Closure:
- “alright, lab time is just about up. Put all your equipment back where you found it,
collect your notes and head back to our room”
• ask students to take their seats
- “I want everybody to think about this, and I'll ask someone in a minute. What was the
objective of today's lesson?”
– after a minute, call on someone to answer
– ask who agrees, or disagrees
- discuss how what they've learned applies to
• situations at home
• situations at work
- ask each student to individually to rate out of ten how well they understood the lesson
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and state what they'd like to have clarified
Evaluation:
- formal
• mark pre-, and post lab questions
- informal
• review the ratings received by students
• adjust this lesson as needed to make it more understandable, or objective more obvious
• adjust next day's lesson to clarify if needed
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Pre-Lab for Gravitational Acceleration (g) Lab
Problem:
What is the acceleration due to gravity (g) experienced by masses having the values of 50
g, 100 g and 150 g?
Prediction:
According to Newton's Second Law, when an object of mass (m) is experiencing an
acceleration – a change in speed, or direction - (a), then there is a force (F) acting on it.
On earth we notice that some force acts on objects “forcing” them toward its surface.
This force is known as the force of gravity (Fg), and the acceleration is known as the
acceleration due to gravity (g).
Physicists have measured this acceleration (g) and have so far determined it to be
approximately 9.81 m/s2.
In this lab, we will find the acceleration due to gravity (g) that a set of known masses
experience due to the force of gravity (Fg), and determine whether or not Newton's
Second Law is valid. If it is, we should get a value close to 9.81 m/s2.
Remember, we are NOT trying to get the “right” answer, we are trying to see for
ourselves if Newton's Second Law deserves to be a law.
Newton's Second Law:
 =m a
F
Fg =m g (g: acceleration due to gravity = a: acceleration)
To find acceleration due to gravity: g =
Fg
m
Experimental Design:
Known masses will be measured on spring scales. The force of gravity (Fg ) will be
determined from the difference between the initial (beginning) and final readings of
force on the spring scale. This value will then be used to see if the acceleration due to
gravity (g) can be found.
Your set of masses includes a 25 g mass, this mass will NOT be used to calculate
acceleration. Some of the scales cannot be set to zero, and have initial readings which are
off of the scale. If your scale has an initial reading which is off of the scale then use the
25 g mass to bring the indicator down into range, and use that as your initial force.
In the initial force column of the the table below, record the beginning position of the
indicator on the scale to the nearest decimal place of a Newton. Add the 50 g mass and
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record its final position in the final force column of the table below. Find the force of
gravity by subtracting the initial force from the final force such that:
Fg = final force−initial force
and record the result in the Fg column in the following table.
Evidence:
mass
(kg)
final force
(N)
Analysis: (show calculations)
initial force
acceleration
Fg
(N)
(m/s2)
(N)
Materials:
one metal stand
one metal clamp
one 2.5 N spring scale
one 25 g mass
one 50 g mass
one 100 g mass
Pre-Lab Questions:
(Give all answers in appropriate SI units so convert as necessary. Remember your
significant digits. Mass (m) is in kilograms when using SI units.)
Given a 50 g mass, calculate Fg if g = 9.81 m/s2. Fg =
Given the same mass, calculate Fg if g = 10 m/s2. Fg =
N
N
A 25 g mass experiences a force of 0.25 N, what is the acceleration of the mass?
g=
m/s2
A 100 g mass experiences a force of 0.981 N, what is the acceleration of the mass?
g=
m/s2
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Procedure for Gravitational Acceleration (g) Lab
1. Record the indicated 50 g of first mass in table using SI units.
2. Record initial force in table.
3. Hang 50 g mass on scale.
4. Record measured force to nearest decimal place of a Newton in table, and in 50 g mass
row.
5. Record the indicated 100 g of second mass in table using SI units.
6. Record initial force in table.
7. Hang 100 g mass on scale.
8. Record measured force to nearest decimal place of a Newton in table, and in 100 g
mass row.
9. Record the indicated 150 g of third mass in table using SI units.
10.Record initial force in table.
11.Hang 150 g mass on scale.
12.Record measured force to the nearest decimal place of a Newton in table, and in 150 g
mass row.
13.Use the evidence collected to calculate the acceleration for 50 g mass.
14.Record calculated values in table in record book in the 50 g mass row.
15.Repeat steps 14 and 15 for the evidence collected for the 100 g and the 150 g masses.
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Post lab for Gravitational Acceleration (g) Lab
Analysis:(Record results in table. Remember Significant Digits.)
Convert grams to kilograms:
50 g =
kg
100 g =
kg
150 g =
kg
Determining force of gravity:
Fg = final force−intial force
Calculations of acceleration due to gravity: g =
Calculate the percent difference: diff =
Fg
m
 g −9.81 m/ s 2 
9.81 m/ s 2 
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Evaluation:
Based on percent difference was Newton's Second Law verified, or falsified?
Error of scale: ±0.05 N
Error of masses: ±0.5 g
Total error:
What does the total error say about the experiment?
How good a test of acceleration due to gravity do you think the experiment was?
How easy did you find the procedure to follow?
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Synthesis:
1. If we repeated this experiment in Australia, could you expect the results to be similar,
or different? How about in Russia, or Nigeria?
2. The value we found was obtained close to the earth's surface. Do you think the result
might have been different if we were up on a mountain? How about in an airplane, or
in orbit aboard the space shuttle?
3. Can Newton's Second Law tell us anything about the acceleration due to gravity of the
Moon? How would you test it?
4. Assuming that you could survive, how about on the surface of the Sun?
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5. If you performed this lab, but kept getting a result of 20 N, you did not make any
mistakes during the lab, and your equipment was working properly, what could you
say about Newton's Second Law?
6. What would have to happen before scientists would accept what your evidence says
about Newton's Second Law?
7. There are cases, such as buoyancy, which seem to defy the claim that earth's gravity
pulls things to its surface. Based on what you have learned in this lab, can you think
of a reasonable explanation of why this appears to be the case, and how you might test
it?