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Classroom Activity Theme: Motion Title: Newton’s Cradle The National Science Center One Seventh Street on Riverwalk Augusta, Georgia 30901 1-800-325-5445 www.NationalScienceCenter.org 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. The National Science Center 1 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. The National Science Center 2 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. The National Science Center 3