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

ITEM # PX-9103
\$99.00
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PX-9103

Paul Hewitt teaches: Momentum, Energy, Center of Gravity, and 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:

1. 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

2. 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

3. 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

4. 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.]