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04 SwabDeck & Balance v1 (2)

Name: _____________________________
SASP 2011
Part A:
Swab the Deck
Get this:
 one alcohol prep swab packet
Do this:
Tear open the packet and pull out the prep swab. Do NOT unfold the swab.
Drag the swab across the table top to make a wet streak about one foot long.
1. Watch the streak for a minute or two. Describe what you see and smell. Use words
and pictures. (Do NOT try to explain what happens; just describe what happens.)
2. Now explain what happened to the alcohol streak. Give your best guess:
Where do you think the alcohol went? Why did it do this? Use words and pictures.
3. In question 2, you came up with an explanation. Now think of an alternative
explanation – a different way to explain where the alcohol went. (Think of how
someone else might try to explain it.) Use words and pictures.
4. In questions 2 and 3 above, you came up with two ways to explain what happened.
Now suppose you want to test these two ideas to see which explanation is better.
Think of some simple experiments that you could do to test these two explanations.
Part B:
Get these:
Do this:
Swab Balance
thick marker pen (such as a white board marker)
masking tape
plastic ruler
new alcohol prep swab packet
Read these three steps first BEFORE you start doing any of them:
Step (A): Lay the marker pen on its side on the table top, and tape the pen onto the
table so that it cannot roll. Lay the ruler across the pen so the ruler
balances horizontally on top of the pen (the pen acts as a fulcrum).
Step (B): Now open the alcohol swab packet, pull out the prep swab – DO NOT unfold
the swab – and immediately lay the wet swab on the right end of the ruler.
Notice that this makes the right half of the ruler drop down, since the
swab makes the right half heavier than the left half.
Step (C): QUICKLY but carefully reposition the ruler slightly on the fulcrum (the pen)
so that the ruler is perfectly balanced horizontally; now there should be a
little more of the ruler’s length on the left side of the fulcrum than on the
right side, to compensate for the extra weight of the swab.
As soon as the ruler is perfectly balanced, do not touch it.
5. Watch the balance for a few minutes. What happens? Simply describe; don’t explain.
6. Suppose Pam says, “I think matter is made of tiny particles.” Do your observations in
question 5 seem to agree with Pam? Why or why not?
7. The activities on this page used alcohol. If you tried all of these same activities with
water instead of alcohol…
a) … in what ways do you think the results would be the same as for the alcohol?
b) …in what ways do you think the results would be different from the alcohol? Why?
The two activities “Swab the Deck” and “Swab Balance” lead you to some very important class
discussion about the idea that the world is made of tiny particles. Be sure to read through both
sections below called “Whole-class discussion”.
Intended Learning Outcomes
Students will understand the following:
 The process of evaporation is most easily explained if we think of the liquid as being made of tiny
particles. (Important: The teacher will not use the word “evaporation” and will ask students not to
use it either.)
 More than one possible explanation is usually possible and even plausible for many phenomena
(including explanations that we might not initially believe are valid).
 A good explanation fits the observations we make of a phenomena.
 A good explanation prepares us to makes predictions for future experiments.
Supplies for Part A — “Swab the Deck”
Alcohol swabs - one sealed packet for every group of
students. (These are sold in the medical
supply section of many variety stores; they
come in small square tear-open packets.
You can substitute cotton balls dipped into
rubbing alcohol.)
Supplies for Part B — “Alcohol Balance”
alcohol swabs again - one sealed packet for every group of students
thick marking pens (or something similar in shape, to act as a simple fulcrum for the ruler)
masking tape
12-inch ruler (or something similar in shape, made of plastic, not wood; it will act as a balance)
Optional: White boards and white-board pens
Safety Note
Because rubbing alcohol is flammable, be sure there are no open flames or sources of high
heat/sparks near the swabs.
Class Time Needed
Part A – Swab the Deck: 1520 minutes
(This is time for small groups to do the initial procedure and complete questions # 1-4,
especially if they are thoughtful about answering the questions.)
Class discussion before Part B: At least 10 minutes.
Part B – Swab Balance: 1015 minutes
(This is time for small groups to do the procedure and answer the questions if they
understand the set-up.)
Student’s Prior Knowledge
& Experience
It is highly recommended that you have
students do the previous activity with a
sugar cube, “How Small?” In that activity,
you will have introduced to the class the
central theme of this entire unit—a theme
that we can pose as a question:
Is it reasonable to say that all
things in the world around us
(or at least most things) are
made of extremely tiny
The question above will guide all of the
activities and discussions for the rest of
this unit. In future activities, the question
will be turned into a model called the
“Particle Model of Matter”. At the
moment, however, the students are not yet
ready to call it a model. For now, we will
simply say to them that we are “proposing
the idea” or “asking the question”: Is all
the world made of tiny particles? The
activities over the next couple of weeks
are designed to let students test this
proposal and see if it makes sense of the
world around them.
The activity “Swab the Deck” is intended to give students some first-hand evidence in your class for
the Particle Model of Matter.
Lesson Outline and Teaching Suggestions
Introducing Part A: “Swab the Deck”
Ask students to remind you of the main discoveries in the sugar cube investigation. One key finding:
We found that sugar cubes can be broken down into smaller and smaller particles, so small that we
had trouble seeing them with our eyes. Based on this finding, we raised a new question:
“Can all things (or at least most things) be broken down smaller and smaller into tiny
bits or pieces or particles?”
Write this question on the board, and tell students that it will be the central theme of the next couple of
weeks. Tell them that today’s activity will be a way to begin testing that question/proposal.
Pass out the handout, “Swab the Deck”. Before you let them get started, you might need to tell them a
few things – and NOT tell them a few things:
 If you think students will misunderstand the procedure with the swab (the “Do this” section),
demonstrate it briefly for them—or at least act out how to do the procedure .
 DO NOT tell them what to expect. Yes, you know the alcohol will seem to disappear or
“evaporate”, but do not tell that to the students, even if you think they already expect it to
happen. Let them discover it. DO NOT use the word “evaporate”. A student can easily say
“The alcohol evaporated” and sound knowledgeable but have no idea what evaporation
really means (i.e. have no idea what the alcohol really did).
 Tell them to do only Part A — stop at the bottom of the first side of the student handout.
They will get to do Part B soon, but not until the teacher tells them to do it.
 Point out to them the difference between question 1 and question 2 — the difference
between “observing” and “explaining”. This distinction is very important.
During the activity (students working in small groups)
After these initial instructions, get the students working. As they work in groups, wander around the
room and make sure of these things:
 They should be talking to each other within the group about what they are seeing/thinking.
 Make sure they remember to simply “observe” in question 1 – they are writing only the facts that
their eyes saw and their noses smelled. They should not make any inferences in question 1, such
as “the alcohol evaporated” or “the alcohol got absorbed into the table”. Inferences like these
should go into question 2.
 Look and listen for students who might be using the word “evaporate”. If they do use it, tell them
something like, “Our class doesn’t know what that word means, at least not yet. Can you explain
what happened without using fancy science words? If the alcohol is not visible on the table top
anymore, can it be found somewhere else now? Where? How did it get there?”
 Students sometimes need some help with question 3. They can think of only their own best
explanation but not an alternative. As you continue to wander from group to group, if you find a
group that can’t think of an alternative, you might give them a prompt like, “What might other
students in this class think happened?” or “What might a student a few years younger than you think
happened?” If they still can’t think of anything, you can suggest some possibilities, such as “Could
someone think the alcohol simply vanished into nothingness – it doesn’t exist anymore?” or “Could
someone think the table is like a sponge?”
Check to see how quickly the groups get to questions 3 and 4. Some groups move quickly, and others
move more slowly; this is normal. If some groups finish question 4 and start getting impatient, you
may decide to stop the group activity time and begin the whole-class discussion of Part A before the
other groups finish question 4.
Whole-class discussion after Part A
Goals for the whole class discussion:
a) Review some of the answers that students wrote for the questions.
b) Help students focus on the ideas that are most important to today’s theme;
help students set aside details or ideas that are not important.
c) Help students listen to each other and see that not everyone sees the same things or comes up
with the same explanations.
d) Give students some practice respectfully debating and defending their ideas.
e) Bring the class to some consensus about which ideas/explanations are most reasonable
(based on evidence).
f) Prepare students for what activities/experiments they will be doing next.
Question 1
You might start by asking the students to give you examples of things they wrote for question 1. As
students respond, you might want to make a list on the board of what they say.
Here are some things to watch out for during this discussion:
 Do not give your own answers; let the students generate the list of observations. If they are
overlooking anything important, prompt them with questions.
 Do not evaluate their answers as “right” or “wrong”, and don’t allow other students to criticize
any of the ideas. If they disagree with an idea, tell them they will have a chance to speak up
 As much as possible, try to write down a student’s idea in his/her own words.
 If a student’s idea is unclear to you or you think it may be unclear to other students, ask the
student to clarify. You can ask questions like, “Do you mean that you saw…?” or “Can you
tell me what you mean by that word?”
 If a response seems like an inference (an explanation or conclusion) instead of a simple
observation, such as “I saw it evaporate”, here are two possible ways you can respond:
 “I don’t think we all understand that word. What did it actually look like to your eyes?”
 “It sounds like you have an idea for how to explain what you actually saw. We will get to
explanations in a moment. What did your eyes actually see that made you think of that
 If a student’s ideas seems “wrong” to you, you can simply write it down with the other ideas.
If it is insignificant, you can probably ignore it. On the other hand, if you think it will cause
significant misunderstanding among students, and you can’t decide how to steer around it,
write it down for now and then deal with it a few minutes later by asking the class, “Let’s
review our list of ideas. Raise a hand if you saw observation 1… observation 2… ” Take a
quick look around the room as you read through the list. When you get to the item that you
think is a problem, see if the number of hands is small enough for you to respond, “Oh, so
not very many of you saw this one… the alcohol streak normally doesn’t do this.” If a lot of
hands go up, you can say, “This observation is interesting… the alcohol streak usually
doesn’t do this one. I’m going to make a note of it, and maybe we’ll figure this one out later.”
Here are some common answers to question 1 (not all groups saw or wrote all of these):
 Initially the alcohol made a long wet streak across the table top.
 The steak began to disappear fairly quickly.
 The streak did not disappear evenly; one end might have disappeared before the other; the
long edges might have disappeared before the middle.
 The disappearance did not proceed in a consistent direction; patches of the streak
disappeared in random places, leaving unconnected remaining patches of wetness.
 There are some spots or “stains” on the table top where the alcohol used to be.
After you have generated a reasonable list, give students a chance to make any final comments about
the list.
Question 2 and 3
After discussing question 1, elicit ideas for questions 2 and 3 together – possible explanations for what
happened to the alcohol. Write them on the board -- all responses, even ones that you don’t think are
good explanations, as long as they are an attempt to explain why the alcohol seemed to disappear.
Typical answers include, but are not limited to, these:
Explanation (a): The alcohol went into the air.
Explanation (b): The alcohol got absorbed into the table.
Explanation (c): The alcohol simply “dried up” or vanished – it does not exist anymore.
When the students are done offering ideas, you might ask something like the following:
How should we decide which explanation is best? Do scientists decide by voting? Do they go
to the courthouse and ask a judge? Do they advertise on TV or the internet to sell their ideas?
Do they decide by having debates on TV?
Sometimes students think that scientists choose an explanation simply because “it is correct”. But real
scientists usually don’t know which explanation is truly correct, and there is no one they can ask who
knows more than they do about it. Real science is not simply answering questions in a science book,
and we can’t simply ask Mr. Know-It-All to tell us the right answers. We are trying to figure out the real
world, and there is no one who has it all figured out for certain. We come up with the best theory we
can for today, using the information we know today, knowing that tomorrow we may discover new
information that shows that today’s theories were wrong.
Students should come to realize that a minimum requirement of a good explanation is this: It fits the
data; it can explain all the observations that we have made so far. A good explanation should be able
to do more than this, as we will later see, but this is a good starting point.
You can use this idea to help the class evaluate the various explanations you have written on the
board. For example: Most students would agree the “vanishing into non-existence” explanation has
trouble explaining one important observation — students could smell the alcohol around the room, as
if it was “floating in the air”. Try to help the students narrow down the list of possible explanations by
helping them think of observations (facts, not opinions) that might argue against some of the
So, after thinking about all the evidence so far, what if your class ends up with two or three
explanations that can explain the alcohol observations? Then perhaps you can try to devise “tests” or
experiments to see which explanation continues to explain any new data you might possibly gather.
This is the point of question 4, and it is also the point of Part B: Swab Balance. Part B will devise a
test for the explanation that the alcohol got absorbed into the table.
Before you introduce Part B, be sure to leave the possible explanations on the board, especially the
ones that your class has not yet ruled out.
Introducing Part B: “Swab Balance”
In the activity “Swab the Deck”, some students may wonder if the alcohol streak is being absorbed into
the table top, even after class discussion. This second activity, “Swab Balance”, will help most
students see that absorption is NOT the best explanation.
It is likely students will need you to briefly demonstrate the procedure (the “Do This” section) before
they do it themselves. If you demonstrate it, highlight these ideas:
 Steps (a) and (b): First, without the swab, make your ruler act as a see-saw-type balance,
with the marker-pen acting as the fulcrum. Comment that you should make sure there are
no significant air drafts blowing on your ruler.
 Step (c): Next, put the freshly-opened wet swab on the right end of the ruler. The swab’s
weight should make the ruler drop down slightly, so now adjust the ruler to re-balance it on
the fulcrum. It should look horizontal when you have it adjusted correctly.
 Now comment that you need patience. You need to watch the ruler without touching it for a
few minutes. You can tell them what kind of effect you will look for: “See if the swab end of
the ruler goes up, goes down, or stays exactly level.” But DO NOT tell them which of these
three options is correct; let them discover it for themselves.
 Stop your demonstration as soon as you have re-positioned the ruler at the end of Step (c);
do NOT give your demo enough time for the swab to dry out and make the ruler tilt.
During the activity (students working in small groups)
When students do this activity for themselves, if they set it up correctly, eventually they should see the
ruler tilt slightly up on the swab end (and down on the opposite end). Occasionally one or two groups
in the class may not see this result, but most groups should, if they did the set-up carefully and waited
patiently. Those who did not see it tilt up can simply look at a neighboring group’s ruler.
Question 7 (the prediction) is not essential; it is OK if faster-working groups have time to answer it but
slower-working groups do not.
Whole-class discussion after Part B
Ask the class what they saw the ruler do in this activity. Then go back to the board where you
previously listed some possible explanations for the disappearing alcohol swipe at the end of Part A.
Ask them which possibility best explains what happened to the ruler. Most students should agree that
the swab-end of the ruler got lighter and tilted up because the alcohol left it and went into the air.
Now press the class further on this issue. Refer them back to the alcohol swipe across the table top in
Part A. Did the alcohol leave the table top all in one piece, like an invisible ribbon of alcohol that
gradually lifted off the table and is now floating in the room intact (though invisible)? Remind them of
something they should have seen—the streak of alcohol on the table top disappeared unevenly; one
patch of the streak disappeared first, then another, and then another, etc. What does this suggest
about the alcohol? It suggests that the alcohol separated into parts, perhaps small bits or pieces, as it
left the table and went into the air. This is indeed the proposal we made at the beginning of Part A:
Maybe all things in the world around us (or at least most things) are made of extremely
tiny particles.
If it is not already there, write the above statement onto the blackboard. It is the main theme of the
entire unit, and you want students to see keep it forefront in their minds.
This is a good time to have students use the whiteboards. Have each group draw a couple of
diagrams: One diagram showing the table top with a fresh layer of alcohol particles on it, and another
diagram showing where those particles are a minute later (after many of them have left the table top).
Emphasize that their drawings should show particles of alcohol — not simply a layer of alcohol.
Here are some common drawings of the alcohol streak at the beginning and then more than half-way
through the process (air particles are not shown):
Some useful follow-up questions
To wrap up your discussion today, and to prepare students for some important ideas they will see in
up-coming activities, here are two final questions you might ask:
Question 1:
“Eventually all of the alcohol particles left the table top. What do you think made them leave?
Why do you think they didn’t simply stay on the table top?”
Encourage them to suggest (guess) some possible answers. Common student answers:
 The air steals the alcohol particles away. (Teacher might reply: So, do they stick to the air a
 The alcohol particles have some motion (or get moving), and one by one they fly off, away
from the remaining alcohol particles.
 Air currents blow them off the table.
Question 2 (this will be the theme of the next activity “Drops Away”):
“Water can sit for quite a long time on a table top before disappearing. (See student handout
question 7.) Why do you think water particles don’t leave as fast as alcohol particles?”
Common student answers:
 Water particles are heavier.
 Water particles are not moving as fast as alcohol particles.
 Water particles stick to each other better than alcohol particles do.
The point here is NOT to get the “correct answer” but instead to get students wondering. On the other
hand, if students suggest the following two ideas, you might emphasize them and write them down
(perhaps as questions), because they will be important themes in the Particle Model:
Could these tiny particles we are talking about have MOTION?
Could these tiny particles we are talking about have some kind of STICKINESS – some
way they cling or attract each other?
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