Prior
Knowledge:
Guiding
Questions:
Learning
Objectives:
Benchmarks:
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Conservation of Cookie Matter PLUS
SC.4.P.8.3: Explore the Law of Conservation of Mass by demonstrating that the mass of a whole object
is always the same as the sum of the masses of its parts.
SC.4.N.1.4: Attempt reasonable answers to scientific questions and cite evidence in support.
SC.4.N.1.5: Compare the methods and results of investigations done by other classmates.
SC.4.N.1.6: Keep records that describe observations made, carefully distinguishing actual observations
from ideas and inferences about the observations.
The students will be able to:
• Describe a closed system;
• Explain why mass is not changed in a closed system, regardless of what is done to the object;
• Make observations and inferences based on those observations;
• Distinguish between observations and inferences;
• Compare methodology of different groups and explain differences in results across the groups.
Guiding questions are broad questions that the teacher can use to “guide” the student learning
process and can be revisited at any point in the lesson.
Teacher Note: In this activity, students will be learning a very important foundational Science concept:
the mass of a closed system will not change, no matter what you do to the parts, as long as the system
remains closed. This science law is important to understanding in every field of science. The questions
below are important questions that the teacher needs to keep in mind as the investigation unfolds.
• Is it possible for something to change and yet remain the same? (Yes, no matter what you do to an
object in a closed system, the mass will always stay the same.)
• How can human actions impact the results of a scientific investigation? (If the scientist doesn’t
carefully control the experiment, different results can result.)
• How do changes affect the mass of an object?
Students should know that inferences are based on observation They should also know how to compare
the observations made by different groups using the same tools and seek reasons to explain the
differences across groups. They should also know how to measure and compare the mass of objects.
(All are grade 3 benchmarks).
Students should also know the states of matter (liquid and solid) for Part 3.
Submitted by: Wendy Shelden, TASK-Force Resource Guide, Brevard Public Schools
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Materials:
Classroom Management:
Each of the parts of this activity could be used as your whole-class Science Project and individual/team
projects.
Part 1 should take 1-2 class periods (depending on whether you are introducing the Science Fair
process). Part 2 (dried foods) should take 1 class period. Part 3 (ice pops) should only take one class
period, but needs to be separated by several hours to allow time for freezing. Part 4 (grow gator) only
takes about 15 minutes to set it up, then 3-5 minutes a day to check for the next week. One class period
at the end would be ideal to discuss all the investigations.
The most important part of each part of this investigation is controlling the variables—this is what causes
most of the differences in data. Some areas to watch out for:
 Cookies/Dried Food Items (parts 1-2): The cookies must stay in the sealed plastic bags—even
while the students are breaking them and crushing them. That way you are measuring the
combined mass of the pieces and none escaped. If you open and close the bag, you are letting air
in and out, and we know that air has at least a little bit of mass. To model how important this step
is, do the experiment once when you take the cookies out to break them apart. When you weigh
them, the mass is different because part of the cookie mass was left on the table you smashed them
on. This shows the students the importance of controlling your variables. If the bag gets a hole,
that’s an invalid trial.
 Ice Pops (part 3): You have to wipe off the condensation that is frozen to the outside of the pop,
and it will try to re-condense as soon as you wipe it off. So you have to be very quick about getting
the condensation off before finding the mass.
 Gator in the bottle (part 4): Make sure you place the bottle in the same spot on the scale each
time.
Part 1:
~Cookies (2 per student)
~Zippered plastic bags
~Digital scale
Part 2:
~Zippered plastic bags
~Digital scale
Part 3:
~Ice Pops (1 per student)
~Masking tape
~Permanent marker
~Digital scale
~Freezer
Part 4:
~1 empty 2-liter bottle
with lid
~water to fill bottle
~1 “grow gator”
~Digital scale
Engage:
Make up zippered plastic bags with 2 whole cookies per bag. Only make enough bags of whole cookies
for each student in the class. Also make a few bags with 2 cookies broken into pieces and a few with 2
cookies completely pulverized in to crumbs.
As the students come into class, tell them to grab a bag of cookies. They will probably all grab the whole
cookies. Go over to get your bag of cookies and complain loudly that there are only little pieces left. Try
to exchange bags with the students. If they won’t exchange with you ask, “Why not?” Try to get the
students to say there are more cookies in the whole bags than the pieces bags. If no one says that, then
say, “It’s not fair, your bags have more.” When the kids either laugh or tell you they are all the same
mass, challenge them to help you design a Science investigation to check their hypotheses.
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These directions are for Part 1: Cookies. Part 2, 3, and 4 use this same format, but you just need to
make the appropriate changes based on the new objects being investigated.
Teacher Note: There is a Student Inquiry Lab Report (included at the end of the lesson). It is intended
as a template to help the students keep track of the parts of a science experiment.
Explore:
1. Explain that you are going to design an experiment to test whether the mass of an object changes
when you break it apart. The first thing to do is identify the variables. The independent variable is
the thing you are changing in the experiment. What are we changing? (the number of pieces: 1, 5, or
many) The dependent variable is what we are measuring. What are we measuring? (the mass of
the cookies) Control variables are all the other things in the experiment that must be kept exactly the
same so that we have results we can depend on (scientifically valid results). Ask the students to list
the things that have to be kept the same for a fair (valid) test. Your final variables should look
something like this:
Variables:
Independent-Number of pieces of the cookies (crushed, pieces, or whole)
Dependent-Mass of the cookies
Controlled-number of cookies you started with; same bag; same amount of air in bag;
same scale each time; same person reading the scale each time; repeated trials
(everyone in the class will do it), same cookies for each round of trials, same kind of
cookies, etc.
2. The second step is using the variables to write a question. Model how to write the following question:
Question: How does the number of pieces (independent variable) affect the mass
(dependent variable) of the cookies (topic of experiment)?
3. Model writing an “If…, then…” hypothesis. Everyone does NOT have to have the same hypothesis,
but they do all have to have a justification for their hypotheses.
Hypothesis: If I measure the mass (dependent variable) of cookies that are whole
or in pieces (control variable), then the whole cookie (independent variable condition
that the student thinks will have the most change) will have a mass that is 5 grams
more (needs quantity) than the cookie pieces. I think this will happen because the
cookie loses mass as it is broken. (Justification)
4. Now you are ready to design the Procedure. Work the students through the steps. Guide them to a
fair test by using the control variables. Your Procedure might look something like this:
Procedure:
1) Place 2 whole cookies in a zippered bag. Seal the bag after getting most of the air
out.
2) Find the mass of 2 whole cookies in a sealed bag. Record on data chart.
3) Without opening the bag, break the cookies into bite-sized pieces.
4) Using the same method and scale as Step 2, find the mass of the broken pieces in
the sealed bag. Record.
5) Without opening the bag, pulverize the cookies.
6) Using the same method and scale as Step 2, find the mass of the pulverized
cookies in the sealed bag. Record.
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Explore, Part 2:
Explore, (continued)
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Conservation of Cookie Matter PLUS
5. The next step after designing a Procedure is making a Data Chart. Again, guide the students
through constructing their own Data Chart. Use the one on the Student Inquiry Lab Report as a
guide for you.
6. Once you’ve designed the Data Chart, have the students begin their trials. Monitor the scales to
make sure they are following the procedure. Do not let anyone throw out the bag of cookies at the
end.
7. Check the results with the students. Everyone should have results showing that the mass didn’t
change at all. If some have differences, ask another student to inspect that student’s bag, looking for
holes. Then have the first student go through the procedure again with a new bag of cookies, with
the second student acting as Observer to verify that the control variables were controlled. This
usually helps point out any errors.
8. Once all the results are verified, guide the students to an understanding that the zippered bag
creates a “closed system.” As long as the bag isn’t opened, the mass of the bag and its contents will
not change, regardless of what you do to it. As soon as you open the bag, you’ve opened the
system, and the mass could change.
9. Draw conclusions about how the size of the pieces affected the mass of the cookies.
Conclusion: My data (does or does not) support my hypothesis. My hypothesis stated
that ____(give full hypothesis)_____ , and my data showed that the mass of the cookies
didn’t change at all. I think this happened because the zippered bag created a closed
system. As long as it was closed, nothing could change the mass of the cookies.
10. If you are using this as a Science Fair process, continue on with the Summary. Then proceed to
Part 2.
Part 2: Dry Food
 Give each child a new zippered bag. Tell them to take it home and put a dry food item in the
bag. Some suggestions are chips and cereal. Explain that they will be repeating the
investigation with items of their choice tomorrow.
 On the next day, go over the variables, question, hypothesis, and procedure from Part 1. Ask,
“What do we need to change? The only change should be to substitute the new item for the
word cookie.
HINT: In the Science notebook, you can have the students write the new question and
hypothesis, but for the procedure, just write: “Follow procedure from Part 1.”
 Also, remind the students to think about their hypothesis. Caution: Do not tell them that the
mass should be the same—let them come to that understanding on their own. Don’t worry
if some continue to think that the mass will change. The fact that the mass stays the
same is counter-intuitive. The students will need lots of evidence to get them to change
their minds, which they will get with Parts 2, 3, and 4.
 Follow Steps 7-8 above to test and discuss the results. Again, if anyone has different results,
assign an Observer.
Submitted by: Wendy Shelden, TASK-Force Resource Guide, Brevard Public Schools
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Explore, Part 4:
Explore, Part 3:
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Conservation of Cookie Matter PLUS
Part 3: Ice Pops
 Give each student a room temperature Ice Pop. Show them how to fold the ice pop in half, wrap
masking tape around the ice pop several times to hold it in half, then use a permanent marker to
write his/her name on the pop.
 Explain that you are going to be freezing the ice pop. This time, the independent variable is the
state of matter (liquid or solid). Guide them in changing the question and writing a new
hypothesis. Again, don’t tell them what to expect. Students know that ice expands, so
they will expect the mass to increase.
 Ask if the procedure needs to change. (Yes, we aren’t breaking it into pieces; we are putting it in
a freezer for ___ hours. Also, they will need to add a step for wiping off all the condensation/frost
on the outside of the frozen ice pop before weighing it.)
 Test the ice pops and discuss the results as you did for Parts 1 & 2.
Part 4: Grow Gator
 This investigation is done by the teacher only. Fill a 2-liter bottle with water. Push one “grow
gator” (available at www.stevespanglerscience.com) into the bottle and replace the lid tightly.
Make sure you dry off any external water drops!
 Place the bottle on the scale, placing it directly in the middle of the scale. Record the mass of the
bottle on the board, then place the bottle up high on a shelf where everyone can see it, but no
students can touch it or mess with it.
 Explain that we will be leaving the bottle on the shelf, but taking it down each morning to find the
mass and make any observations. Explain to the students that the gator is a “grow gator.” Don’t
tell them anything else!
 Guide them in changing the question and writing a new hypothesis. Again, don’t tell them what
to expect. This is where they really have to face their misconceptions.
 Each morning, take down the bottle, weigh it in exactly the same place and record the results on
the board (and in the Science notebooks). Encourage the students to also record any
observations they make. (Possible observations: the gator is getting larger; the water level is
dropping.)
 At the end of the week, find the mass of the bottle one more time. The mass should not have
changed, even though the gator got noticeably larger.
Submitted by: Wendy Shelden, TASK-Force Resource Guide, Brevard Public Schools
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Evaluate:
Elaborate:
Explain:
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Conservation of Cookie Matter PLUS
As you discuss the results of all the investigations, ask the students the following questions:
 Why did the mass stay the same, even though the gator got noticeably larger? (The 2L bottle is a
CLOSED SYSTEM. As long as it remains closed, nothing can get in or out—the mass (amount of
matter) inside remains the same, regardless of what physical changes take place within the bottle.
The gator absorbed lots of water that made its size bigger, but there was still the same amount of
mass in the bottle.)
 Why did the mass stay the same, even though the water level dropped? (same as above)
 Compare the “grow gator” experiment to the ice pops and cookie experiment. Why did you get the
same results? (All are examples of CLOSED SYSTEMS—nothing gets in and nothing gets out, so
the mass remains the same.)
 Why did we occasionally get different results? (Sometimes it was that we couldn’t control every
variable—especially with the ice pops condensation problem. Most of the time, though, it was due
to human error.)
 Go over the observations they made during Part 4. Lead a discussion on whether they are all
observations, or if some inferences crept in. If they wrote, “The gator is getting larger.”—that’s an
observation. If they wrote, “The mass is increasing.” or “I think…..”—those are inferences.
If you used this as a Science Fair project introduction, add these questions:
 Is there a component of the Scientific Method that we didn’t do? (Yes, Research)
 What could we have researched to help us make a better Hypothesis? (Accept all plausible
answers; some possibilities: mass, scales, how cookies are packaged to prevent breakage.)
Ask the students to design their own investigation testing the mass in a closed system. Some
possibilities:
 cereal and milk
 an apple as it decays (sealed in a plastic bag)
Diagnostic and/or formative assessments are embedded within the lesson for the purpose of
identifying preconceptions and driving instruction so the students have increased opportunities
to learn the important ideas related to the topic.
Summative Assessment:
Give students the “Seedlings in a Jar” probe from Page Keeley’s Uncovering Student Ideas in Science,
Volume 1. This is another example of a closed system.
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Student Inquiry Lab Report
Use this format to plan out your investigation. Record all parts in your
Science notebook or Science Fair log.
Identify variables:

Independent variable (condition you are changing)_______________________

Dependent variable (what are your measuring)____________________________

Control variable (all other conditions to be kept the same)___________________
______________________________________________________________________
Problem: How does (independent variable) affect the (dependent variable) of
(controlled variable)?
How does __________________________ affect the ______________________ of
__________________________________?
Hypothesis: Use your variables again: If I measure the (dependent variable) of
(control variable), then the (independent variable) will (do what?).
If I measure the __________________________________ of ___________________,
then the ___________________________________ will ________________________
_________________________________________________________. I think this will
happen because ________________________________________________________.
Procedure/Materials: Write on another piece of paper.
Data/Results: What is the best way to record the data you observed? Chart, graph,
illustrations? Use a separate sheet of paper for this so you have plenty of room.
Conclusions: My data (does or does not) support my hypothesis. My hypothesis
stated that ____(give full hypothesis)_____ , and my data showed that the mass of the
cookies didn’t change at all. I think this happened because ______________________
______________________________________________________________________.
Share and Communicate: What is the best way to Communicate your experiment
and Results with the class or others?
Submitted by: Wendy Shelden, TASK-Force Resource Guide, Brevard Public Schools
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Conservation of Cookie Matter
Data Chart
Mass of
Whole cookies
(in grams)
Mass of
Large Chunks (in
grams)
Mass of Crumbs
(in grams)
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Trial 6
Trial 7
Trial 8
Trial 9
Trial 10
Submitted by: Wendy Shelden, TASK-Force Resource Guide, Brevard Public Schools
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Conservation of Ice Pop Matter
Data Chart
Mass of
room temp Pop
(in grams)
Mass of
frozen Pop
(in grams)
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Trial 6
Trial 7
Trial 8
Trial 9
Trial 10
Submitted by: Wendy Shelden, TASK-Force Resource Guide, Brevard Public Schools
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