Friday, February 15, 2008

• Group assignments will soon be posted.  Any changes require the consent of all students involved.
• Here is a correlation analysis of Exam1 performance versus various parameters.
  

Assignments:

• Answer the recommended conceptual exercises and problems for Chapter 7, and check your understanding by looking at the answers in the back of the textbook.
• Let me know your 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%.

How could you estimate the maximum power output of a typical human? (Prob. 6.22)

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

Chapter 7 - Second Law of Thermodynamics (you can't even break even)

Zeroth law of thermodynamics - When two objects  have the same temperature, they are in thermal equilibrium.
First law of thermodynamics - Energy cannot be created or destroyed:  The change in internal energy of an object is the heat added to it minus the work done by the object.
Second law of thermodynamics -  When objects of different temperatures are brought into thermal contact, the spontaneous flow of heat is always from higher to lower temperature, never the reverse direction.  The total entropy (disorder) of a system cannot decrease over time.
Third law of thermodynamics - It is impossible to reach absolute zero  K.