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WHAT IS ENERGY?

The ability to do work

LAWS OF THERMODYNAMICS

- 1st Law:

Energy can be changed from one form to another, but cannot be created or destroyed

- 2nd Law:

Energy tends to change from a more ordered to a less ordered form; in other words, entropy increases.

Entropy = the amount of energy not able to do work.

LAWS OF THERMODYNAMICS

- Explain the 2 laws of thermodynamics using the previous example
- How is the energy we consume measured ?

CONVERSIONS

ENERGY CONVERSIONS:

http://www.onlineconversions.com/energy.htm

TEMPERATURE CONVERSIONS:

http://www.onlineconversions.com/temperature.com

ENERGY CONVERSIONS

when energy changes from one form to another, we say that some of the energy is “lost”, but what we mean is that some of the energy is dissipated to the surrounding environment as heat.

When we use energy it is best to use it by changing its form as few times as possible.

AN EXAMPLE: MAKING TEA

In a rural village in China:

- Sun
- Plant / tree
- Harvest by human
- Match
- Hot water

In the US:

- Sun
- Fossil fuel
- Mining using machines
- Processing
- Shipping using truck, etc.
- Electrical generation
- Heating element on stove
- Hot water

ENERGY CONSUMPTION

- Per person, the most industrialized nations use up to 100 times more energy than do the least industrialized nations
- For example, the US has only 5% of the world’s population, but consumes 23% of the world’s energy
- Developed and developing nations “spend” their energy differently
- developed nations spend 1/3 of their energy on transportation, 1/3 on industry, and 1/3 on everything else
- Developing nations spend most of their energy on agriculture, food preparation, and home heating; very little on transportation

LESSON LEARNED: USE ENERGY EFFICIENTLY

Efficient energy consumption is difficult to determine if we don’t know how to measure energy consumption…

Measuring energy consumption requires the conversion of units commonly used to measure different forms of energy – see the “Energy Consumption” worksheet:

ENERGY CONSUMPTION WORKSHEET

- Heating and Air Conditioning
- Heating Water (1 kWh costs $0.19)
- Electrical Appliances – microwave question only!

FOLLOW THE DIRECTIONS ON THE WORKSHEET – ASK IF YOU DO NOT KNOW HOW TO COMPLETE A STEP!

HEATING and AC

- 21.96 ft2
- 75 F – 34 F = 41 F
- Heat change = 21.96 ft2 X 41 F / 1.85

= 486.7 BTU / hr

- 24 X 365 = hrs / year = 8760 ; 486.7 BTU X 8760 hr = 4,263,492 BTU / yr
- 21.96 ft2 X 36 F / 1.85 = 427.3 BTU / hr
- 10.98 ft2 X 41 F / 1.85 = 243.3 BTU / hr
- 21.96 ft2 X 41 F / 2.8 = 321.6 BTU / hr

Solve this!

How many gallons of oil could be saved in one year if one window was removed from this room?

How many gallons of oil could be saved in one year if one window was removed from each classroom in this building? (73 rooms)

HEATING WATER

- 81 grams water in 5mins = 972 g / hr
- 972 g / 454 = 2.1 lbs / hr
- 2.1 X 8760 = 18,396 lbs / yr
- 120 F – 40 F = 80 F increase in temperature
- 1 BTU raises 1 lb water 1 F ;

18,396 lbs X 80 F = 1,471,680 BTUs

- 1 kWh = 3412 BTU ; 1,471,680 / 3412 = 431 kWh
- 431 kWh X $0.19 = $81.89

MICROWAVE

Watts is the energy used per hour

- 975 W X 50 hrs = 48,750 W used in a year
- 48,750 W = 48.75 kW
- 3412 BTU X 48.75 kW = 166,335 BTU
- 166,335 BTU / 145,000 BTU = 1.15 gals oil

HOMEWORK

- Read Chapter 21 pages 603 – 625
- Complete “Energy Use Of Home Appliances”

3. Work on your energy project – remember, it is due April 30!!!

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