Wednesday, February 13, 2008

• Reflection paper - submit for class participation credit:  Why was performance on Exam1 so low?  What could you have done (and hopefully will do next time) to better prepare for this exam?
• I will be assigning groups very soon, so let me know if you have a particular preference for who you would like to work with for the Web Project.  Keep in mind that groups cannot have more than 4 members.

Assignments:

• Answer the recommended conceptual exercises and problems for Chapter 6, and check your understanding by looking at the answers in the back of the textbook.
• Read Chapter 7 and come to class prepared to discuss.
• Test corrections are due next Monday
• Begin thinking about topic ideas for your physics Web Project

Energy is physics' most important concept.
Fundamental physics principle - Conservation of Energy:  E = constant in the Universe
Energy is the ability to do work:  W = F*d

Energy can be in various forms:

• Gravitational Potential Energy:  GravE = mgh
• Kinetic Energy:  KinE = 1/2mv²
• Rotational Kinetic Energy:  RotE = 1/2Iw²
• Elastic Potential Energy:  ElastE = 1/2kx²
• Electromagnetic (light, magnetic fields):  ElectE
  
• Heat (from friction, air resistance):  ThermE
  
• Sound (from collision, explosion):  SoundE
  
• Light:  RadE
  
• Chemical energy (battery):  ChemE
  
• Nuclear:  NuclE
  

How high can you hike using the energy consumed by a 300-Calorie candy bar?  Assume a metabolic efficiency of 10%.

Bowling ball demo - How much energy is dissipated in one oscillation?  How efficient is this system?
Balls rolling down 3 different tracks of same height - How do the final speeds compare?  Which is the fastest track?

Work:  W = F*d  (vector dot product)   d = distance through which the force is exerted
    Compare the work done by a long ramp versus a short one.

Power:  P = W/dt   (rate that work is done)  measured in Watts (W) or horsepower (HP):  1 HP = 750 W
    Estimate 1 human-power (as opposed to horse power).

Ponderable:  Do we pay for electrical power or energy?

Identify the energy transformations that apply to the following situations:
- Ball rolling down a hill
- Car going over a bump in the road
- Flashlight operating (note incorrect answer for CE #29)
- Lightning
- Nuclear bomb exploding

In groups of 2 or 3, identify as many examples as possible for each of the following energy tranformations.  Extra credit will be awarded to the top 3 groups.

1. KinE -> ThermE
2. ThermE -> KinE
3. RadE -> ChemE
4. RadE -> KinE
5. KinE -> ElectE
   

Many people claim to have invented perpetual motion machines.  Why is this not possible?
http://en.wikipedia.org/wiki/Perpetual_motion

Examples of heat engines:  automobile, power plant