Forces and Newton's Laws
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Does It Have to
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Two friends are arguing about forces. They disagree about whether something has to
be touched in order for a force to act. This is what they say:
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Akiko: "I think two things have to touch in order to have a force between them."
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Fern:
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Which friend do you most agree with? _ _ _ __
"I don't think two things have to touch in order to have a force between them."
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Explain YOut thinking. Ptovide examples that support your ideas about forces.
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Uncovering Student Ideas in Physical Science
75
Forces and Newton's Laws
Does It Have to Touch?
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Purpose
or repelling each other). The action-at-a-distance
The purpose of this assessment probe is to elicit
beginning ideas about types of forces. The
probe is designed to reveal whether students
recognize that forces can act both in direct
contact with an object and at a distance.
forces can also act when they are in contact with
an object, such as a hall resting on the ground, a
nail stuck to a magnet, or a piece of paper stuck
to an electrically charged balloon.
Related Concepts
action-at-a-distance force, contact force
Explanation
Fern has the best answer: "I don't think two
things have to touch in order to have a force
between them," Forces can act between objects
without the objects being in contact with each
other. Forces can involve direct contact between
objects (such as a person pulling a wagon or
pushing a cart) or action at a distance (such as a
ball being pulled toward the Earth by gravity, a
magnet attracting or repelling another magnet,
or two electrically charged balloons attracting
76
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Administering the Probe
This probe is best used in the elementary grades
after students have developed the concept of
force as a push or pull. It can be used when
students have learned ahout forces they have
experienced through direct contact and are
ready to learn abo~t different types of forces
that act at a distance, such as gravity, magnetic
force, and electrical force. If needed, clarify
what is meant by touched in the probe. In this
context touch means direct, physical contact
between two things, such as kicking a ball.
The probe is also useful in uncovering middle
school students' preconceptions about forces.
National Science Teachers Association
1
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Forces and Newton's Laws
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Related Ideas in National
Science Education Standards
(NRC 1996)
charged or negatively charged. Two objects
K-4 Position and Motion of Objects
attraction on each other.
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The position and motion of objects can be
changed by pushing or pulling,
that are charged in the same manner exert
a force of repulsion on each other, while
oppositely charged objects exert a force of
Related Research
•
K-4 Light, Heat, Electricity, and
Magnetism
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Related Ideas in Benchmarks
for Science Literacy
(AAAS 1993, 2009)
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K-2 Forces of Nature
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Things ncar the earth fall to the ground
unless something holds them up.
Magnets can be used to make some things
move without being touched.
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3-5 Forces of Nature
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The earth's gravity pulls any object toward
it without touching it.
Without touching them, a magnet pulls on
all things made of iron and either pushes
or pulls on other magnets.
Without touching them, material that has
been electrically charged pulls on all other
materials and may either push or pull other
charged materials.
6-8 Forces of Nature
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and other planets in their orbits, just as
the planets' gravitational pull keeps their
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A charged object can be charged in one of
two ways,
which
we call either positively
living things, physical activity, and muscular strength (Driver et a1. 1994).
Elementary students typically do not understand gravity as a force. They see "falling" as
a natural action by an object (AAAS 1993).
Students often describe electric and magnetic interactions without using words
that distinguish among forces, properties
of matter, and fields. This is an example of
a common student difficulty related to the
difference between a cause and an effect
(Andersson 1985).
A study of children ages 3-9 (Selman
et a1. 1982) found two different conceptual
levels of thinking about magnetism. At the
first level, children appeared to be simply
linking events, without the notion of force
being involved. At the second level, chilchen demonstrated an emerging notion of
an "unseen force" and they began to talk
about a magnet "pulling on things" (Driver
et a1. 1994).
Suggestions for Instruction and
Assessment
'The sun's gravitational pull holds the earth
moons in orbit around them.
Electric currents and magnets can exert a
force on each other.
Younger students tend to bring lay meanings of the word force to their learning. They
often associate the word force with coercion,
Magnets attract and repel each other and
certain kinds of materials.
@
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Present student.s with examples of forces
and ask them to decide which ones are
pulls and which are pushes. Then ask
them to decide which ones involve contact
between objects and which do not.
Younger students should first have opportunities to experience pushes and pulls
with contact forces. Later, once they
understand the idea of forces that act at
*: Indicates a strong match between the ideas elicited by the probe and a national standard's learning goal.
Uncovering Student Ideas in Physical Science
77
Forces and Newton's laws
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a distance, they can explore pushes and
pulls with falling objects, magnets, and
electrically charged objects.
Because gravity, magnetic force, and the
force between electrically charged objects
cannot be seen, children need to grasp the
concept of action at a distance by observing
its effects. Give students multiple opportunities to see these effects and to describe
them as pushes or pulls.
Students need to recognize that with the
exception ofgravitational, magnetic, and electric forces, no other forces act at a distance.
eracy online. www.project2061.orglpublicationsl
bsllonline
Andersson, B. 1985. the experiential gestalt of causation: A common core to pupils' preconceptions
in science. Gothenburg, Sweden: University of
Gothenburg, Department of Education and
Educational Research.
Driver, R., A. Squires, P. Rushworth, and V WoodRobinson. 1994. Making sense of secondary
science: Research into children's ideas. London:
RoutledgeFalmer.
National Research Council (NRC). 1996. National
science education standards. Washington, DC:
References
American Association for the Advancement of Science (AAAS). 1993. Benchmarksjor science literacy. New York: Oxford University Press.
American A'isociation for the Advancement of Science (AAAS). 2009. Benchmarks for science lit-
78
National Academics Press.
Selman, R., M. Krupa, C. Stone, and D. Jacquette.
1982. Concrete operational thoughts and the
emergence of the concept of unseen force in
children's theories of electromagnetism and
gravity. Science Education 66 (2): 181-194.
National Science Teachers Association