Energy

The many different forms of energy are interchangeable, and the total amount of energy in an isolated system is conserved.

Key terms:

Work (measured in Joules or J)

Energy (measured in joules or J)

Power (measured in watts, W or kilowatts kW)

Watt

Kilowatt

Kinetic energy

Potential energy

Thermal energy (heat)

Wave energy

Trophic level

Conservation law

System

Frist law of thermodynamics

Fuel cell

Equations and Constants:

W=fdwork in Joules = force in Newtons x distance meters

E = Ptenergy in Joules = power in watts x time in secs

KE = ½ mv2kinetic energy in joules = ½ mass in kilograms x (velocity in m/s)2

GPE = mghmass in kilograms x g x height in meters

E = mc2energy associated with mass at rest in Joules = mass in kilograms x (speed of light in m/s)2

c = speed of light = 3 x 10 8 m/s

Review Questions:

  1. What is the scientific definition work?
  2. How does the scientific definition differ from ordinary everyday use of the word?
  3. What is a Joule?
  4. Differentiate between energy and power.
  5. What is the unit of power?
  6. Relate speed to power.
  7. How do mass and speed relate to kinetic energy? Be specific; give examples.
  8. Explain how sound is actually a form of energy.
  9. How do sound waves travel?
  10. Give examples of changes of energy form kinetic to potential and potential to kinetic.
  11. What is a trophic level? Give an example.
  12. How much energy is transferred or “lost” at each trophic level?
  13. Does the total amount of energy in an isolated system change over time? Explain your answer.
  14. Is mass a form of energy? Why or why not?
  15. How did the discovery that mass is a form of energy resolve the debate over the Earth’s age?
  16. Explain the following statement: Energy flows through the Earth.

Discussion Questions:

  1. What kinds of energy are used in the following:

  1. Surfing
  2. NASCAR racing
  3. Hang gliding
  4. Skiing
  5. Golf
  6. Mountain climbing

  1. What forms of energy are you using when you:
  2. Start your car
  3. Run up the stairs
  4. Dry your clothes
  5. Where does geothermal energy come from? Is it a renewable energy source?
  1. Is hydroelectricity a renewable energy source? Explain your answer.
  1. Is it possible to use alternative energy sources to meet the current energy demands of the United States?
  1. What are some of the environmental costs of the alternative energy sources?
  1. Define fossil fuels.
  1. How are coal and oil forms of solar energy?
  1. Plants and animals are still dying and falling to the bottoms of ocean floors toady. Why then do we not classify fossil fuels as renewable energy sources?
  1. Ancient civilizations are described as labor intensive while modern society is said to be energy intensive. Explain what is meant by these terms.
  1. How do warm blooded animals warm their blood? What form of energy do “cold blooded animals use to warm their blood and bodies?

Problems:

  1. How much work against gravity do you perform when you walk up a flight of stairs five meters high (assuming that your body mass is 75 kg)?
  2. Compare the work done to that done by a 100-watt light bulb in one hour.
  3. How many times would you have to walk up those stairs to equal the work of the light bulb in one hour?
  4. Which has more gravitational potential energy:
  5. A 200-kg boulder 1 meter off the ground
  6. A 50-kg boulder 4 meters off the ground
  7. 1 kg boulder 200 meters off the ground
  8. Of the boulders in problem 29, which can do the most work if all the GPE is converted to KE?
  9. Compared to a car moving 10 mph, how much KE does the same car have when it moves 20 mph? 50 mph? 75 mph?
  10. Graph your results
  11. What does the graph suggest about the difficulty of stopping a car as its speed increases?
  12. According to Einstein’s famous equation, E=mc2, how much energy would be released is a pound of feathers was converted entirely into energy? (to convert pounds to kilograms, take the number of pounds and divide by 2.2)
  13. A pound of lead?
  14. If you eat 600 calories / day ( approx.. one large order of fries) above your energy needs, how long will it take you gain 20 pounds?
  15. How long will you have to walk to burn off those 20 pounds? (Assume 80 calories burned / mile walked)
  16. If the process of beef is $2.50 / pound, estimate what the price of lion meat might be, and give reasons for your prediction.
  17. Why are both forms of meat more expensive, pound for pound, than carrots?
  18. Joules and kilowatt hours are both units of energy. How many joules are equal to 1 kilowatt hour?

Investigations:

38.Look at your most recent electric bill and fins the cost of one kilowatt hour in your area. Then:

a. Look at the back of your CD player or an appliance and find the power rating in watts. How much does it cost for you to operate the device for one hour?

b. If you leave a 100 watt light bulb on all the time, how much will you pay in a year of electric bills?

39.Keep a record of the calorie content of the food you eat and the amount of exercise you do for one week. If you wanted to either lose or gain a pound per month, how might you change your current habits?

40.Rub your hands together for several seconds. What energy conversion is occurring?

EC If you work out on a stationary bike at a power output of 100 watts for 30 min, does the energy output compensate for eating a 250 calorie jelly filled doughnut? (Assume that the body converts 20% of the energy input to work and the other 80% is lost as heat and movement) 1 food calorie = 1 kilocalorie 1 calorie = 4.2 kilojoules