Conceptual Physics Alive: Momentum, Energy, Center of Gravity & Rotation

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 4 Episodes: Episode 1: Momentum: Newton's 2nd law is rearranged to the form: Impulse = Change in Momentum. A variety of everyday examples, such as bouncing are used to support this impulse-momentum concept. Conservation of momentum is demonstrated with colliding carts on an air track. Segment length: 50 minutes Episode 2: Energy: Mechanical energy in its potential and kinetic forms is illustrated with demonstrations that include a bouncing dart, a pendulum, and a simple pulley system. The conservation of energy is illuminated using everyday examples and a hand-cranked electric generator. Segment length: 48 minutes Episode 3: Center of Gravity: The concepts of torque, center of gravity, and center of mass are applied to balancing. Demonstrations include finding the center of gravity of irregularly-shaped objects, a weighted disk that rolls uphill, and a seesaw. Segment length: 33 minutes Episode 4: Rotation: The concept of rotational inertia is developed from a variety of everyday examples and demonstrations using weighted objects, and rolling cans filled with both liquids and solids. Finally, Paul stands on a rotating turntable to demonstrate angular momentum. Segment length: 46 minutes Momentum includes: • Hewitt begins with comparison of mass and moving mass momentum. • Impulse and momentum are defined. • Delta notation introduced. • Examples of impulse-momentum: Golf ball, Slingshot, Cannonballs shot from short and long cannons, Car with failed brakes, Jumping into a net, Riding with the punch when boxing, and Catching a baseball • Distinction between impact and impulse. • Bouncing and its effect on impulse. Karate and Pelton wheel • Demonstration of elastic colli sions on an air track. • Demonstration of inelastic collisions on an air track. • Definition of a system. Pushing on automobile dashboard. • Momentum conservation. • Railroad cars example. Next-Time Question: Demo of the swinging balls apparatus: Why will two balls not eject one ball at twice the speed? [Although momentum would be conserved, there would be twice the KE.] Energy includes: • Begins with a review of momentum, and poses questions that support the concept of impulse. • Hewitt demonstrates momentum transfer by a swinging dart that hits a wooden block. The greater impulse of bouncing is demonstrated. • "How long" in terms of distance, rather than time, produces work. • Work-energy relationship introduced; Fd = energy. • Forms of energy are compared. • Energy of motion; kinetic energy (KE). • Cannonball shot from a short and a longer cannon. • Demonstration of a bowling ball pendulum pulled with a spring scale to show the force variation with angle. • Demonstration of energy transfer from potential to kinetic with the bowling ball pendulum. • Conservation of energy. • Chalkboard sketches of conservation of energy • Demonstration of the work done in raising a mass with different forces. • Machines. • Car jack. • Raising a piano with pulleys. • Energy to drive an automobile. • Efficiency. • Demonstration of turning a generator to light a lamp. Paul is assisted by Meidor, a regular visitor. • Gasoline mileage and applying a cigarette tighter in a car, and driving with lights on. • Skidding distance for a car. • Superball demonstration for humor. Next-Time Questions: A section of a racquet ball is inverted (giving it elastic potential energy) and dropped. It bounces higher from the table than its initial position. Why? [When it struck the table it became uninverted and its elastic potential energy sent it higher than gravitational potential energy alone.) Will it always bounce higher? [No, there is an initial height to which it won't bounce higher.] Where is that height? [The same additional height the inverted ball will reach if it reinverts from a rest position on the table.] Center of Gravity includes: • Begins by Hewitt throwing a ball and wooden object through the air to introduce center of gravity (CG) and center of mass. • Center of gravity of L-shaped wood and irregular piece of wood found by suspension technique. • Hewitt demonstrates the toppling of L-shaped wood, and introduces the concept of torque. • The CG of people is discussed. • Hewitt demonstrates the impossibility of toe touching with heels to the wall, with follow-up chalkboard explanation. • Pregnant lady and CG skit. • CG examples: pigeon walk, monkeys, and dinosaur tail. • Trucks on a hill are sketched on board to illustrate CG. • Demonstration of a 'loaded' disk rolling up an incline. • See saws, CG, and torque. • Solitary see saw discussed. • Hewitt saws a broom in half at its CG. Next Time Question: Which weighs more, the broom or the sawed-off broom handle, or do both weigh the same? [Although both produce the same torque about the fulcrum (CG), the broom part weighs more, as evidenced by its closer distance to the fulcrum.] Rotation includes: • Hewitt begins with review of acceleration and force to tie into rotational acceleration and torque. • Rotational inertia introduced. • Demonstration of plastic pipes with lead inserts shaken by students and visitor Tenny Lim. • Demonstrations of balancing a hammer and a lead-weighted stick. • Discussion of flywheels. • Demonstration of dropping two meter sticks, one weighted. • A pendulum swing is demonstrated, and pendulum rate of walking for different creatures compared. • Tightrope walker and rotational inertia. • Demonstration of a wooden dowel rolling down incline. • Demonstration and comparison of a rolling disk and ring down incline. • Hewitt demonstrates angular momentum on a rotating platform. • Rotational speed and linear speed compared by coins rotating at different radii on a rotating platform. • Hewitt swings a water-filled bucket overhead. • Centrifugal and centripetal force compared. • Examples of centripetal force: driving in a car, whirling ball on string, people in rotating space colony, ants in bicycle wheel. • Space station sketched on board and discussed. Next Time Question: Which rolls faster down an incline, a can of pineapple juice or a can of chili beans? [Juice, because liquid slides within rolling can without rotational inertia. Beans. On the other hand, are made to roll because they act like a solid.]