Conceptual Physics Alive: Newton's 1st, 2nd, 3rd Laws
Master teacher Paul Hewitt teaches non-computational Conceptual Physics. Observe Hewitt teach in a classroom with real students, using engaging demonstrations and artwork.
DVD Includes 3 Episodes:
Episode 1: Newton's 1st Law: The law of inertia and the concept of mass are introduced and supported with a variety of examples and intriguing demonstrations, such as the tablecloth-and-dishes stunt. The concepts of net force and statics are also illustrated.
Segment length: 45 minutes
Episode 2: Newton's 2nd Law: The relationship of force, acceleration, and mass is illustrated with a variety of examples. The effects of friction on motion are shown using both sliding and falling objects. Segment length: 42 minutes
Episode 3: Newton's 3rd Law: The notion that a force is a push or a pull is developed. The concept that forces always occur in pairs as interactions between one thing and another is supported with numerous examples, including a tug-of-war. Segment length: 43 minutes
Newton's 1st Law includes:
• Hewitt begins by lifting a heavy anvil and discusses the motion the anvil would experience with impressed forces.
• Historical perspective; Aristotle on motion; cannonballs and arrows.
• Newton's 1st law; inertia.
• Blobs of clay are suspended by a coat hanger on Paul's head. How can he see the blob at the back of his head? [By simply turning around; the blobs stay put and demonstrate inertia.]
• Weight and mass are distinguished.
• Block of wood (mass) on a piece of cloth are shown. Hewitt asks, 'When yanked, will the block follow the cloth, stay put, or recoil in the opposite direction?' [For humor it follows the cloth, but only because it has been stapled to the cloth!]
• Demonstration of dishes on a tablecloth, where the cloth is rapidly pulled beneath the dishes.
• Demo repeated with more massive metal cylinder.
• Cylinder is rolled across a table, to demonstrate that in the absence of an impressed force a body in motion tends to remain in motion.
• Concept of net force is explained.
• Examples illustrate that inertia is a resistance to change.
• Demonstration of hanging ball and the breaking of strings. This demo compares the role of weight and the role of mass in string breakage.
• Sledgehammer-and-anvil demo, where Hewitt puts the anvil on his stomach and is hit by the hammer.
• The example of tightening a hammerhead on a handle illustrates a body in motion tends to remain in motion, which leads to the explanation of why people are shorter at nighttime.
• Story of Hewitt painting signs with Burl Grey, and how their discussions of physics changed Hewitt's life. Hewitt poses some of the questions asked by Burl.
• Story of Harry the painter who rearranges the rope support in his bossun's chair, with devastating consequences because of his ignorance of physics.
Next-Time Question: Why is Harry's last day on the job prompted by his act of tying one end of the rope to the flagpole? [With only one strand to support him, the tension in the strand would have to be his whole weight, 200 pounds. But the rope has dry rot and will only support 150 pounds. So the rope breaks and Harry falls (fortunately an untrue story).]
Newton's 2nd Law includes:
• Hewitt begins with historic evidence against earth at rest.
• Coin flipping while undergoing accelerated motion.
• Zero acceleration and zero net force.
• Newton as a unit of force.
• Demonstration of a block dragged across the table with a force-measuring scale.
• Questions highlight the concepts of force and acceleration.
• Airplane thrust and drag.
• The concept of mass.
• Comparison of a= (change in v)/t, what acceleration is, and a= F/m, how acceleration is produced.
• Galilee compared to Newton.
• Kid skit on falling masses; development of Newton's 2nd law.
• Newton's 2nd law as a guide to thinking.
• Rollercoaster example of Newton's 2nd law.
• Parachute example of Newton's 2nd law.
• Air resistance.
• Terminal velocity.
Newton’s 3rd Law includes:
• Hewitt begins with "I can't touch you without you touching me in return." Then Newton's 3rd law is defined.
• Force defined as an interaction.
• Demonstration of blocks pulled by elastic band.
• Demonstration of a tug of war with visitor, Helen Yan (co-author of the Next-Time Questions that accompanies the high school edition of Hewitt's Conceptual Physics).
• Fingers stretching a rubber band produce a single interaction. Likewise with the gravitational interaction between the earth and moon.
• Action, A on B; Reaction, B on A.
• Examples of walking on floor; swimming, tires pushing road, tug of war, pulling up on bike handlebars, weighing oneself and pulling up (or pushing down) on sink, dropping an object.
• Different accelerations shown with exaggerated symbols.
• Examples of gun kick, firing squad, rocket fired to the moon, being stranded on ice, and punching a sheet of paper.
Next-Time Question: Horse-and-cart problem sketched on board: How can the horse exert a force to move the cart when the cart exerts as much reaction force? [The answer to this is best understood by defining the "system" the force acts upon. If the system is simply the cart, then the force the horse exerts will accelerate the cart. The fact that the cart reacts on the horse is of no consequence to the cart. If the system is the horse, then two horizontal forces act; the reaction to the horse's push against the ground, and the reaction by the cart on the horse. If the reaction by the ground is greater, the horse accelerates in that direction. If the system is taken to be the horse and cart together, the force that moves the system is the reaction of the horse's push against the ground.]