11/10/10

Post date: Nov 09, 2010 8:57:5 PM

    • Bell Ringer: A 3.00 kg Chihuahua is roller skating at 1.5 m/sec. a) How much KE does it have? b) If 50 N of forward force are applied to it over 5 meters, how much KE will it have? c) How fast does it move afterward?

    • Return and discuss quizzes

    • Conservation of energy notes

      • Energy can never be created or destroyed, but it does change forms and locations easily

      • Total energy in a system does not change

      • Ei = Ef

      • example: Car rolling down a hill

    • Energy flow diagrams

      • Since energy transforms so readily, it is useful to have a clear way to picture where the energy goes

      • Box energy type at each point, make notes in parentheses below boxes

      • Show energy transformations as arrows from one box to another.

      • Each box ends up with multiple arrows coming from it, can label each with a percentage to show efficiencies.

      • Almost all energy can be traced back to the sun (matter), and all matter can be traced back to the big bang (when it was transformed from energy into matter). Before that ... who knows?

      • example: ball rolling down a ramp

      • example: ball rolling through a loop

      • example: brick pendulum

      • example: Tom Hanks fire

    • How to solve conservation or energy problems

      • Draw free body diagram for time period of interest

      • Decide what types of energy are present in "initial" and "final" states

      • Write a conservation equation: (Initial energy type a) + (Initial energy type b) + (Initial energy type c) ... = (final energy type z) + (final energy type y) + (final energy type x) ...

      • Plug in numbers or equations for each energy type, and solve for unknowns.

      • example: Superman leaping a tall building in a single bound