Key Concepts:

1. What is energy? And what is conservation of energy?
2. What is momentum and angular momentum?
3. What does conservation of momentum and angular momentum mean?
4. What is escape velocity?
5. How are light and energy related?

Energy = Capacity to Do Work

• Potential Energy
  • gravity: gravitational potential energy (e.g. hydroelectric dam)
  E_G = -GMm/R
  • electro-magnetic: electric and chemical potential energy (e.g. battery, lunch)
  E_q = kQq/R
  • weak/strong force: nuclear energy (e.g. Homer Simpson)
  
  Mass energy:
• Kinetic Energy: energy of motion (includes thermal or heat energy)
E_k = 1/2 mV²
• Temperature is a measure of kinetic energy.
Thermal energy: E_T = 3/2kT
• Radiative Energy: energy carried by light (e.g. heat lamp)
  Photon energy:

Conservation of Energy

Quiz 8A: a firm belief in physics...

Conservation of Momentum and Angular Momentum

• Momentum = (mass) x (velocity)
• A spectacular demonstration of momentum conservation
• Quiz 8B: Evil Twin Skateboarder...
• Angular Momentum = (mass) x (velocity) x (radius)



• Kepler's Second Law: As a planet moves around its orbit, it sweeps out equal areas in equal times.

Escape Velocity

• When you throw a ball straight up, the harder you throw, the higher it goes.


• If thrown hard enough (at high enough velocity), the ball will "escape" Earth.

Quiz 8C: Escape from the Moon...

Light (Radiation)

• Thermal Radiation:temperature/heat (e.g. cafeteria heat lamp, the Sun)
• Non-thermal Radiation:charged particles (e.g. microwave oven, radio pulsar)
• Jackyl & Hyde: wave-like & particle-like

Ocean Wave is: a mechanical train of energy travels through a medium has characteristic speed and lengths

Light = radiant energy. Wave-like ("Electromagnetic Wave"): alternation of magnetic and electric energy transport energy, interact with atoms has characteristic speed and lengths Particle-like (photon): packets of energy: travel in straight line (e.g. laser)

Reading assignment for next lecture: Units 23-25