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Background Information
This Tracing Origins activity is the second in a series of three
“Thought Experiments.” Scientists use thought experiments
when it is not possible to actually conduct real experiments with
real equipment. In Activity
1, students traced the origins of pizza ingredients back to
atoms, the building blocks of matter. But atoms have their own building
blocks—protons, neutrons, and electrons; and protons and neutrons
have their own “fundamental particles”—quarks.
In this second activity students will explore the characteristics
of quarks. Quarks and electrons may have been among the first stable
particles formed in the early universe. At the conclusion students
will be challenged by the question, “If electrons exist as
free particles in the universe today, why aren’t quarks free
particles today?”
This question will be the basis for the final activity of the series,
“Tracing the Origins of Our Universe.” Students will
combine the “tracing process” they used in the first
activity to trace quarks and electrons backwards in time to discover
what important role these fundamental particles may have played
in those early cosmic periods when the universe was in a state of
high density and high energy. This activity will engage students
in a discussion of the energy (temperature) changes that have occurred
from the beginning of the cosmos until now.
| National Science
Education Standards Addressed |
| Grades 5–8 |
| Science As Inquiry
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- Understands about scientific inquiry
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| Physical Science |
- Properties and changes of
properties in matter
- Transfer of energy
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Science
and Technology |
- Understandings about science and technology
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| History and Nature
of Science |
- Nature of science and scientific
knowledge
- History of science and historical
perspective
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| Grades 9-12 Science
As Inquiry |
- Understands about scientific
inquiry
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| Earth and Space Science |
- The origin and evolution of
the universe
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| Physical Science |
- Structure of atoms
- Motions and forces
- Interactions of energy and
matter
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| Science and Technology |
- Understandings about science
and technology
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| History and Nature
of Science |
- Nature of science and scientific
knowledge
- History of science and historical
perspective
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| (View the full text
of the National
Science Education Standards.) |
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| Materials |
| For each pair of students |
| An envelope that contains: |
- Three squares labeled “Ru” = red
up and three labeled “Rd” = red down
- Three squares labeled “Bu” = blue
up and three labeled “Bd” = blue down
- Three squares labeled “Gu” = green
up and three labeled “Gd” = green down
- A PDF template for the braille version of these
squares is available here
or from Tactilelearning.org.
A PDF template for color-coded squares for
use with partially-sighted students can be downloaded
here.
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For
each student: |
 A
copy of Student Activity, “Making Arrangements”- A copy of the Student Text, “Quarks are Fundamental Particles”
- A copy of the Glossary that accompanies the Student Text, “Quarks
are Fundamental Particles”
- An Energetic Electron tactile card which depicts an energetic
electron being deflected by a particle inside a proton.
This can be obtained free of charge by downloading the PDF template
at insert URL here. You can then make thermally-enhanced copies
for your students. Follow the directions
for doing this or you may request The Fundamental Particles Tactile
Card Set, which is available
at cost.
The Student Activity and Student Text materials are available for
use with audio-amplified computer software, 18-point bold
font print copy for partially sighted students, and in Braille for
significantly sight-impaired students. You may select the most appropriate
version of these materials and following these directions.
Note that there are two forms of the Student Texts and Student
Activity available. One includes the phonetic pronunciation of glossary
terms and is written in paragraph form for large print hard copy
readers. The other is suitable for screen readers or braille transcription.
It does not contain the phonetic pronunciation.
An audio tape that contains the student activity the two student
texts, and glossaries is also available.
You may wish to have headsets to use with screen-reading students.
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| Getting Ready |
- Before class make copies of the following
handouts in the form most appropriate for each of your students:
- Student Text, “Quarks are Fundamental
Particles”
- Glossary that accompanies the Student Text,
“Quarks are Fundamental Particles”
- Student Activity, “Making Arrangements”
- Prepare one set of “quark squares”
for each pair of students.
- Prepare (or order) a thermally-enhanced Energetic
Electron tactile card for each student.
- Preview the text material using your audio-amplified
computer software and in Braille. Give your visually-impaired
students any instructions they need to take advantage of their
appropriate learning aids.
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| Background
for Quarks: The Fundamentals of Our Universe |
| In Activity 1, you brought
students to the conclusion that all matter is made of atoms and that
most of the matter on Earth consists of atoms that were formed inside
stars and were distributed through space in earlier supernova explosions.
For many years we have known that protons, neutrons, and electrons
are the building blocks of atoms and that atoms are the building blocks
of matter. In some references, protons and neutrons have been called
fundamental particles, particles that cannot be divided into
smaller particles. It is true that protons and neutrons are stable
particles at temperatures in the universe today, but are they fundamental
particles? Not according to some models of the early universe.
This student activity, “Making Arrangements,"
is designed so that students will discover the combinations of “up”
and “down” quarks that form protons and neutrons. The
use of “flavors” and “colors” to describe
the characteristics of quarks will probably be very new uses of
these terms for both you and your students.
Quarks are very different from any other type of
particle that we usually study. Quarks come in “flavors,"
but not the kind you can taste. There are six flavors, or varieties,
of quarks. Quarks also have assigned characteristic called “color,"
but their “colors” refer to the strong forces that hold
them together, not to their ability to reflect light. It takes one
red, one blue, and one green quark to form a stable particle.
Quarks of the same color repel each other because
they have similar forces, so only one quark of a given color is
found in a stable particle. In addition, no two quarks can form
a particle because their “color” forces would not be
balanced, in the same way that you cannot balance a three-legged
stool on two legs.
Quark’s electrical charges are different from
most charges we are familiar with. They have positive and negative
charges, but the charges are fractions rather than whole numbers.
An “up” quark has a charge of positive two-thirds elementary
charge and a “down” quark has a charge of negative one-third
elementary charge.
You may use the questions in the procedure below
to help clarify the term definitions as well as introduce students
to strong nuclear forces and fractional charges on sub-nuclear particles.
To prepare for using this activity with your students,
you may wish to read (or re-read) “The Universe is Expanding”
and “Remnants of the Big Bang," sections of Appendix
A from the original Cosmic Chemistry: Cosmogony module. Another
excellent background source is The Creation of Matter by Harald
Fritzsch. |
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Procedure |
- Divide students into groups of two. Suggest that they take
turns being the arranger and the recorder.
- Give each group of students an envelope with a set of squares —either
with Braille notations or color-coded—and a copy of the
“Making Arrangements” student activity sheet.
 Tell
students to complete the activity by following the instructions
on the student activity sheet. You may let them work through
all the combinations on their own and then ask for feedback
of their results in a post-activity session. Or, you can help
them read the instructions for the first set of combinations,
have them make their arrangements, and ask for immediate feedback
and comparison of their results. Then go on to the next set
of combinations. - You will probably have to clarify the following instructions
about combinations: “Each square can only be used once
in making a set of combinations. Each combination in a set must
be unique.” For example, the first set of combinations
requires combinations that contain three colors, so they can
have six combinations but all combinations must be unique.
They may not have three sets of Ru, Bu, and Gu squares. Call
attention to the fact that sets that contain the squares of
same color and direction are not unique, so the combinations,
Gu, Bu, Ru and Bu, Gu, Ru, are not different from Ru, Bu, Gu.
 The
instructions for the second set require combinations of two
up and one down squares. Students will probably make different
combinations so you may wish to have students compare
There are four possible combinations of groups with
- 2 up and 1 down squares.
- 1 up and 2 down squares.
There are three possible combinations of groups with
- 2 up and 1 down with three colors
- 1 up and 2 down with three colors
The net charges are:
- The combination of 2 up and 1 down would have a net charge
of +1.
- The combination of 1 up and 2 down would have a net charge
of 0.
- Have students compare their results if they have not already
done so. Then center the discussion on questions similar to
the following:
- Were there any differences in the arrangements of the
different groups?
- What do you think is the significance of the instructions
to:
- Use combinations of three squares?
- Use combinations that included three different
colored squares?
- Use combinations that contained specific numbers
of “up” and “down” squares?
- Find combinations whose net charge is either +1
or 0?
- If none of your students deduced the significance of these
characteristics, point out that they have just modeled the
construction of protons and neutrons from quarks, the fundamental
particles from which all matter is made. The term “fundamental
particles” means that these particles do not decay
into smaller particles. Protons and neutrons are not fundamental
particles because they decay into other particles. Outside
the atomic nucleus, neutrons decay in about 10 minutes.
Protons decay in >1030 years outside the atomic
nucleus. That is a long time but it is not forever.
- Ask if any of your students have heard about or know something
about quarks. If so, use his or her expertise to spark the interest
of other in the class. If not, distribute copies of the Student
Text, “Quarks are Fundamental Particles” as their
reading assignment for the next class period.
- In the follow-up discussion period, use questions similar
to the following to review the characteristics of quarks:
- What are some properties (or characteristics)of quarks?
[flavor, color, fractional electric charge, associated with
gluons]
- How are these properties similar to those of the electron,
the other fundamental particles? [they have mass, electrical
charge, and respond to attractive/repulsive forces]
- How are these properties different from those of an electron?
[electrons have a whole number electric charge, gluon attractive
force increases with distance]
- What four fundamental forces do scientists now recognize?
[gravitational, electromagnetic, weak and strong nuclear
forces] You may have to do some prompting before students
recall some of these kinds of forces. If they have not studied
these forces, be prepared to define them and give examples.
See the text box below for additional background information
on fundamental forces.
- Which of these four fundamental forces plays the most
important role in the behavior of quarks? [strong nuclear]
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- Tell students that until very recently, quarks were “theoretical”
particles. That is, physicists theorized that protons and neutrons
were made of quarks. In the year 2000, scientists in Geneva,
Switzerland used a Super Proton Synchroton to accelerate the
nuclei of lead atoms to 33 trillion electron-volts of energy.
As these nuclei traveled at almost the speed of light, they
were smashed into a stationary lead foil. The resulting collisions
produced hot, dense matter. This new material was a highly compressed
gas of the particles called quarks and gluons, which are the
building blocks of ordinary particles like protons and neutrons.
These quarks and gluons then floated freely in a laboratory
for the first time.
As interesting as this may be, you may be asking why we are
studying such tiny particles during a study of the origin of
the Universe. We think that the universe was comprised of these
tiny particles until about 10 microseconds after its beginning,
when matter was crystallized into the particles we know today.
In the final activity of the module, we will use the process
we used in the pizza activity to trace the origin of quarks.
- End the discussion with the question, “If electrons
are free, stable particles in today’s universe, why aren’t
quarks?” [They may remember how much energy the lead nuclei
had to have to release the quarks in the synchroton. Accept
students’ answers so long as they have a reasonable rationale
for them.] Then tell them that in the next activity, “Tracing
the Origins of Our Universe," they will be exploring the
answer to that question.
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