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Newton’s first law: A learning cycle approach
To demonstrate how Newton’s first law of motion applies to
students’ everyday lives, I developed the following learning
cycle series of activities on inertia. The discrepant event at
the heart of these activities is sure to elicit wide-eyed stares
and puzzled looks from students, but also promote critical
thinking and help bring an abstract concept to life.
Elicitation phase
I use a demonstration called Newton’s Apple for the elicitation phase of the learning cycle. I begin by embedding
the blade of a knife in an apple, just far enough so that the
apple will remain stuck to the blade when the apple is lifted.
(A potato will also work, but an apple is more appropriate
for a lesson on Sir Isaac.) Next, I ask students to predict
what will happen when I gently tap the back of the knife
blade with the blade of a second knife. After the predictions have been made, I begin tapping. Following a few
taps, the apple is cut in half. I always hear some oohs and
aahs or “That’s really cool.” Students record their observations then huddle in their lab groups and attempt to explain them. Often, students will suggest that the knife simply cut through the apple and that the tapping knife forced
it through. Some groups may not be able to offer any explanation. But there is usually a group who will surmise
that somehow, for some reason, the apple was pushing back
on the embedded knife. I accept all inferences with as little
facial expression or body language as possible.
We do not solve the apple problem that day, nor do I
introduce the term inertia. Instead, we move into the exploration phase to investigate an object’s resistance to motion as well as an object’s tendency to remain in motion.
Exploration phase
The first activity in this phase is a teacher demonstration of
the classic magician’s tablecloth trick. Then, students experiment with stacks of coins and blocks to see what happens when a force is applied to the object at the bottom of a
stack. The three activities are completed in about 20 minutes. (See activity sheet for procedures.) Students are then
asked to draw comparisons between the tablecloth demonstration and the stacking activities.
Invention phase
In this phase I introduce the term inertia after a brainstorming session on the similarities among the three activities.
Eventually the class realizes that the major similarity among
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the bowls, coin stack, and block stack is that they are “heavy”
or have mass, which helps them stay in place. I then write
the science term inertia on the board and have students define it aloud in their own words. We agree on the best definition and it is recorded in their notebooks. After further
discussion using everyday examples of how difficult it is to
move common objects in the classroom—such as a loaded
bookcase, a heavy file cabinet, or water-filled aquarium—
students link mass to inertia and realize that an object resists motion because of its inertia. Some students may even
suggest that by emptying the bookcase, file cabinet, or fish
tank they would decrease the mass, which in turn would
decrease the objects’ inertia.
In the next activity, students
use toy cars and small wooden
blocks to further investigate
Newton’s first law of motion. Explore Newton’s first law of
The law also states that, due to motion at www.scilinks.org.
inertia, objects in motion re- Enter code SS020503.
main in motion unless acted upon by an unbalanced
force. Students place a block on a car and then put the
car through a series of sudden stops and starts to observe
what happens to the block. Next, students swing a small
weight (rubber ball) on the end of fishing line (string)
in a circle, and release the line and observe the path of
the weight. Students then compare the two activities.
At this point, students surmise that inertia also keeps an
object in motion and compare the motion of the block in
the car activity to actual human passengers. Inertia is now a
natural part of their vocabulary and an important concept
associated with Newton’s first law is formed.
To bring relevancy to our classroom activities, I ask
one student to sit in a wheeled chair and describe how
they feel as another student begins to push the chair across
the classroom. (Students are reminded to hold on for
safety, but not to brace themselves so they can feel the
forces acting on their body.) The initial comment of the
passenger is usually, “Something is pushing me back in
my seat.” But when I ask the class if they observed anyone or anything pushing their classmate backward, the
passenger acknowledges the misconception. Next, the student is asked to describe how he feels as the chair is pushed
backward across the room. After observing the student
nearly fall out of his seat a few times, students begin to
Deborah McCarthy is a science teacher at the Academy of the Sacred Heart in New Orleans, Louisiana.
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realize that the passenger is at rest
and resists moving because of inertia. When pushed in a forwardfacing position, the back of the
chair back actually pushes the
passenger’s body forward until it
is traveling at the speed of the
chair. Inevitably, a student will
connect the importance of
seatbelts to the sudden stopping
of a car. Inertia causes the body
to continue in motion at the
same speed at which the car was
initially traveling. Students now
understand why passengers without seatbelts are thrown through
the windshield.
Back to the apple
The class is ready to revisit
Newton’s Apple for another attempt at an explanation of what
they observed. After very little
reflection, the chorus is now
“The apple has mass, therefore
inertia, so it wants to stay in
place.” The majority of students
realize that the apple, because of
its mass, has inertia and resists
being moved. When the knife is
struck and begins to move forward, the apple remains in place
and eventually is cut in half as
the knife proceeds forward.
Exploring Newton’s first law of motion
Exploration activities
Magician’s tablecloth
Materials
• woman’s headscarf with a very smooth texture
• heavy bowls
Procedure
1. Place the headscarf on a smooth flat surface.
2. Put two heavy bowls on the edge of the scarf in
the center of a table.
3. Have students predict what will happen when you
quickly pull the scarf from under the bowls.
4. Yank the scarf from beneath the bowls and ask students to describe, record,
and explain what they observed.
Coin columns
Materials (per group)
• 15 or more coins (pennies,
nickels, and even small
washers
are suggested)
Procedure
1. Place 10 coins in a stack.
2. Predict what will happen when you flick another coin at the stack so that it slides
across the table and strikes the edge of the coin on the bottom of the stack. (If
you have trouble sliding a coin into the stack, you can also tap the bottom coin
with a ruler or index card.)
3. Record your observations and try to explain the behavior of the coin that collides
with those in the stack. Describe the behavior of the stack of coins when it is struck.
Knock-a-block
Application phase
Now it’s time for students to apply
their understanding of inertia to a
new, but similar situation. In their
groups, students place an index
card over the mouth of the cup, put
a penny on top at the center of the
cup, and flick the card away causing the penny to drop into the cup.
Students then compare this activity to those in the exploration
phase and explain how they relate
to Newton’s first law.
Materials (per group)
• 3 small wooden blocks (5 cm × 2 cm) for each group (children’s blocks or
dominoes can also be used)
Procedure
1. Make a stack of the three wooden blocks.
2. Predict what will happen when you flick the bottom block with your finger.
3. Record your observations and try to explain the behavior of the bottom block
and the two above.
4. Try the same procedure but flick the middle block.
5. What happens? Why?
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Exploring Newton’s first law of motion
Invention activities
Stop and go
Materials (per group)
• plastic car (15 cm in
length) obtained from a
science supply catalog
or any toy car large enough to carry an object
• one small (5-cm × 2-cm) wooden block (a domino or
child’s wooden block will do)
Procedure
Part A
1. Place the wooden block on edge in the middle of the car.
2. Predict what will happen to the block when you quickly
roll the car to another group member. Sit on the floor
about 1 meter away, place your fingers on the back of
the car, and quickly push it to your partner.
3. Roll the car between group members (resetting the block
before each run), record your observations, and try to
explain the behavior of the block.
Part B
1. Place the block on the car as before.
2. Predict what will happen to the block when you slowly
roll the car to another group member who will gently bring
it to a stop.
3. Record your observations and try to explain the behavior
of the block.
4. Compare the behavior of the block to a passenger in
a moving car that comes to a gradual stop, an abrupt
stop, or an immediate stop when colliding with an
immovable object.
Around and around
Materials (per group)
• scissors
• fishing line or string
• fishing weight or other small object that can be attached
to the line
• safety glasses
Extensions
As a follow-up, I divide the class into two large groups
to discuss the importance of helmets and have them
brainstorm ways to make bicycle helmets more attrac48
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Safety
You will be swinging a weight on a string and releasing it
during this activity. You must wear your safety goggles at all
times during this activity. The weight should be swung as
slowly as possible to prevent it from injuring anyone when
released. Shout a warning before releasing your weight.
Allow plenty of room between your group and other groups.
Procedure
1. Attach the weight to one end of a 10 cm length of
fishing line.
2. Crouch or kneel and spin the weight in a circular motion
2 to 3 cm above and parallel to the floor.
3. Release the line and observe and record the path
traveled by the weight.
4. Repeat this procedure, releasing the weight at several
different points along its path.
5. Create a diagram indicating the direction the weight
traveled based on its release point.
6. Where do you need to release the weight so that it travels
toward you? Away from you? Explain why.
Application activity
Penny drop
Materials (per group)
• penny or washer
• index or playing card
• cup
Procedure
1. Put the playing card over
the mouth of the cup.
2. Place the penny on top of the card in the center of
the cup.
3. Flick the edge of the card with your finger.
4. What happens to the penny? Why?
5. Reset the card and penny.
6. Flick the other edge of the card. Are the results the same?
7. Compare the penny to a passenger standing on a bus
that suddenly lurches forward.
tive to young riders. Some of the incentives to entice
riders to wear helmets are very imaginative and creative.
One group suggested that kits be sold with the helmets
so that the young riders could decorate and personalize
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them. Others suggested that if possible, the helmets
should be designed to be smaller, lighter, and provide
more visibility.
The cognitive rewards of exploring
Beginning a learning cycle with a discrepant event such
as Newton’s Apple hooks my students and helps them
abandon misconceptions and then form and retain the
concepts introduced. They are eager to engage in activities that will answer their questions, and continue their
investigations the next day if the answer isn’t apparent at
the end of science class. As an added bonus, it reinforces
the importance of safe driving and wearing seatbelts.
References
Beisenherz, P., and M. Dantonio. 1996. Using the learning cycle to
teach physical science: A hands-on approach for middle grades. NH:
Heinemann.
Frank, D., J. Little, S. Miller, et al. 2001. Science explorer: Physical
science. Massachusetts: Prentice Hall.
McCarthy, D. 2002. The influence of the integration of a science
history unit addressing the affective domain with the typical
physical science curriculum on the attitudes toward science of
high school females. PhD diss., University of New Orleans.
Marson, R. 1978. Task oriented physical science: Motion. N.P.: Ron
Marson.
National Research Council. 1996. National science education
standards. Washington, DC: National Academy Press.
Connecting to the Standards
This article supports the following National Science Education Standards (NRC 1996):
Content Standards
Grades 5–8
Standard A: Science as Inquiry
Abilities necessary to do scientific inquiry
Understanding about scientific inquiry
Standard B: Physical Science
Motion and forces
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