Energy

1
Energy

• Definition?

2
Lets talk about money first

• Cash flow
• Income
• Spending
• Steady state

Household Dad Mom Kids
Spending
Income
3
Whats Energy?

• Knight Its like natural money
• Ability to do (mechanical) work or change the
  thermal energy of an object (heat up or cool down
  an object) or a system.
• Energy can be transferred to a system or an
  object and stored (like saving money).
• Energy from system can be transferred to an
  object or another system and do work or heat up
  environment (like spending money).
• So energy is a quantity that is stored in a
  system or belongs to an object while work and
  heat are due to interactions with other objects
  or the environment.

4
Energy Conservation

• as opposed to Conservation of Energy
• First refers to a commendable idea of using as
  little energy as possible
• The second is one of the most important laws of
  physics, which we will discuss in a moment.
• We will definitely return to the problem of
  Energy Conservation later.

5
Kinds of Energy

• Mechanical
• Potential gravitational
• Elastic potential
• Kinetic
• Electrical
• Chemical
• Internal thermal
• Radiation
• Nuclear

6
Thermal energy

• Energy of the moving molecules of the object
• Friction PHET simulations
• Demo with carts and springs

7
System energy or total energy

• System energy mechanical energy thermal
  energy
• Esys Emech Eth K U Eth

8
Energy transformations

• U K
• K U
• One can easily transform one kind of mechanical
  energy into an other.
• One can change mechanical energy in a process
  called work.
• Mechanical energy can be converted to thermal
  energy
• U Eth
• K Eth

9
Kinetic Energy

• K m v02 /2
• Kinetic energy of the car
• http//www.metacafe.com/watch/461249/car_crash_mix
  _iii/

10
Gravitational Potential Energy
11
Gravitational Potential Energy

• Ug mgh

12
Potential and Kinetic Energy

• Demo bouncing ball

13
Conservation of Energy

Example (no thermal loss) EKU
14
Energy Diagrams
Energy
Total Energy TE
TE KE PE
KE and PE change as the particle moves from h1 to
h2, but their sum is always the same.
height
h1
h2
KE
PE
15
(No Transcript)
16
Snowboard Manhttp//phet.colorado.edu/new/simulat
ions/sims.php?simEnergy_Skate_Park