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Classroom Activity
Theme: Motion
Title: Newton’s Cradle
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Classroom Activity
Theme:
Topic:
Title:
Motion
Newton Laws of Motion
Newton’s Cradle
National Standard: Physical Science: Content Standard B.
The motion of an object can be described by its position, direction of motion, and speed (B.2.1).
An object that is not being subjected to a force will continue to move at a constant speed and in
a straight line (2.2.2). If more that one force acts on an object along a straight line, then the
force will reinforce or cancel one another, depending on their direction and magnitude.
Unbalance forces will cause changes in the speed or direction of an object’s motion (B.2.3).
Purpose:
To illustrate Newton’s Laws of Motion (Mechanics Section), momentum, kinetic and
potential energy.
Recommended Level: 5-8
Time:
Approximately 10 to 15 minutes.
Materials:
one Newton’s cradle
a desk or table top
Presentation / Procedures:
Acquire a Newton’s cradle. Place the cradle on a tabletop. If the balls are moving, stop them or wait for them to stop. Using the thumb and index
finger, grab a ball on the end and pull it away from the rest of the balls. Release the ball Ask:
What happened? After listening to the responses of the students, stop all of the balls from
moving, raise two balls from the rest of the balls. Ask: What will happen after the balls are
released? One of the responses to both questions will probably be that the ball or balls collided
with the closest ball and caused the others to move. Now, release the balls. When an object is
moving it tends to remain moving in a straight line unless something slows it down, speeds it up
or changes its direction, Newton’s First Law of Motion. Also, when something is not moving, it
will stay in the same position until it is moved by something.
Let students illustrate Newton’s first law of motion using objects in the classroom (the body, a
globe, or a ball). Each of the balls has about the same mass. Therefore, when the ball is
released, it speeds up and collides with the ball that is at rest. The moving ball has momentum
(Linear Momentum and Collisions Section) which means a tendency to remain in motion.
Illustrate momentum and have students provide other examples. The momentum of the raised
ball transfers to the next ball in line. The second ball has no place to go so it transfers the
momentum to the next ball. The process continues until the last ball in line receives the
momentum from all of the previous balls, then it continues on the path of the first ball. The back
and forth process continues until air resistance, friction, and vibrations cause the balls to come
to rest again.
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Classroom Activity
The demonstration also illustrates Newton’s second and third law of motion, potential and
kinetic energy. The second law states that an object accelerates depending on the amount of
force placed on it. Therefore, the amount of mass the ball has determines the amount of force
required to change its position (from raising it up to releasing it). The ball accelerates as it
leaves the fingertip. The stronger the force, the greater the acceleration. As the balls apply
force on each other, each apply an equal and opposite reaction which illustrates Newton’s third
Law of Motion. When the ball is lifted, it is given potential energy. After it is released, the energy
is transformed into a form of motion called kinetic energy. The kinetic energy is transferred as
the balls collide.
After a discussion on potential and kinetic energy, let students demonstrate each. Also, have
students give examples and illustrate how potential energy can be increased.
Expected Outcome: The student will be able to explain and illustrate the laws of motion,
momentum and potential and kinetic energy. The game of pool is another way to help the
students to better understand the concepts covered in this demonstration. Ask if they have ever
played a game of pool. Ask: What will happen if the balls had different masses (the stuff that
they are made of)? Since the balls have the same mass, the transfer of momentum comes out
just right. Ask: What will happen if a very massive ball hits a lighter ball? Tell them to think
about when a baseball bat hits a baseball.
Links: Links used in this activity.
http://guernsey.uoregon.edu/~phdemo/demo/index.html#Mechanics (Mechanics Section)
http://sprott.physics.wisc.edu/demobook/chapter1.htm
http://www.nationalsciencecenter.org/FortDiscovery/Hypercosm3D/coupled_pndlms/coupled_pendulums.htm
http://www.nationalsciencecenter.org/FortDiscovery/Hypercosm3D/newtons_cradle/newtons_cradle.htm
Other links used in this activity.
http://www. NationalScienceCenter.org/FortDiscovery/Hypercosm3D/coupled_pndlms/coupled_pendulums.htm
http://nsc10.nscdiscovery.org/motionsounds/balldrop.htm
http://nsc10.nscdiscovery.org/motionsounds/DynamicsCarts.htm
http://nsc10.nscdiscovery.org/motionsounds/BuckleupBear.htm
http://www.NationalScienceCenter.org/FortDiscovery/MathMotionMomentum/demos/CoupledPendula/CoupledPen
dulaApplet.htm
References:
Barr, B. B., Johnson, G. P. , Leyden, M. B. Physical science (Teacher’s Edition). New
York: Addison-Wesley, 1988.
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Classroom Activity
Hewitt, Paul G., Conceptual physics (2nd ed.). New York: Addison-Wesley, 1998.
Credits:
Swinging Wonder: Newtonian Demonstrator, SNOWCRAFT, 1961 Campground
Road, Hastings, Michigan.
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