Topic: Energy Flow and Matter Cycles

Lesson: Energy and efficiency

Objectives of the lesson

• Realize that energy is needed to overcome disorder/chaos/entropy• Define energy efficiency • Realize that efficiency of different energy convertors vary widely

Introduction – Second law of thermodynamics• The second law of thermodynamics can be stated in three ways• FORM 1: In any transformation of energy from one form to another,

there is always a decrease in the amount of useful energy• FORM 2: Heat cannot, by itself, flow from cold to hot. It

spontaneously flows from hot to cold.• FORM 3: In any closed system, disorder has a natural tendency to• increase.

Introduction -It is a one way Street • In this activity you we looked for order in the world by dumping

pennies on the table /floor. • Pennies landing with the same side up, would indicate order. • If they did not, then you have what is called disorder, chaos,

randomness, or entropy.

Procedure: Questions 6

• A. Describe the system the pennies are part of.• They are pat of a system that includes, the tray, the floor and the

people• B. As the pennies fall to the floor, are they becoming more or less• ordered?

• Why do you think so?• C. To restore the pennies to their original state, what do you need to

add to the system?

Questions –No 7 A

• A. As plants grow, they create order by taking CO2 and H2O and making them into structured plant material (see Figure 3.35). • Are plants violating the second law of thermodynamics? Why or why not?

Q7 A&B

• Plants cannot create order without sunlight powering the photosynthesis process. The sun is the outside force that drive the plant system• B. If there is as much silver in the world today as there always has

been, why are we “running out” of silver?• We are disposing silver in a disorderely manner that requires too

much energy to retrieve it from our dumps. The silver is lost from an economic point of view.

Question 7 C&D

• C. Why can’t automobile exhaust be easily recycled and changed back into gasoline again?• An automobile breaks up orderly gasoline molecules as it extracts

energy from them. It requires energy to put those molecules back together again(recycle them), and this would not make economic sense.• D. How would you explain this statement: “Little children are truly

entropy’s little helpers.• Parents usually like their living space picked up and neat. This is order.• Children have the tendency to take toys and other things out and not

put them away. This is disorder

Q7 –E & F

• E. Iron is extracted from concentrated iron ore and made into thousands of different products, all of which will eventually end up in the hundreds of dumps. Which form of the second law of thermodynamics does this illustrate ? Explain your answer. • Form 3; the iron in the mine is more concentrated (less random) than

the iron that is spread out in landfills. • F. Things tend to go from an orderly condition to one of disorder. To

reverse this process, what must be provided?• Energy

Q7 -G

• G. Relate the balance implied in Figure 3.36 to Form 3 of the second law. Is there balance in our biosphere today? If a balance is achieved , theoretically, how long can human life last on Earth

Q 7 -G

• Plants create order in their structure as they grow . Animals destroy that order as they extract energy from the plant they use for food and fuel. In the process, animals give back to plants the carbon dioxide and water they need for growth. Humans dominate the equation. When we maintain a balance, these energy relationships can be maintained indefinitely.

Energy and Efficiency

• The efficiency of a machine is the ratio of the desired output (work or energy) to the input. As an equation,this becomes the following:• Efficiency (useful energy or work out/energy or work in) 100%• The first law of thermodynamics (the conservation of energy) places a limit on how

high efficiency can go. Since you can’t create energy, no efficiency can be greater than 100 percent.• In most real world situations, efficiencies are much less than 100 percent. For

example, in industry, much energy is lost as heat caused by friction. • For that reason, industrial engineers try to reduce friction. Their efforts have

included machining smooth surfaces, developing new lubricants, inventing better electrical conductors,and so on. • Though the losses may be small, they are still there.

Energy and efficiency

• Any device that converts heat energy into mechanical energy is called a heat engine. Heat engines are important. • The internal combustion engine in our cars, jet engines, and the coal-

fired steam turbines at electric power plants are all examples.• Unfortunately, heat engines are very inefficient.

Efficiencies of various energy converters.

• Devices that are inefficient are at the top of the illustration.

• Devices with high efficiency are at the bottom.

• Note that electric motors, generators and batteries are highly efficient.

• Heat engines are inefficient devices. Heat engines made of metal must be quickly cooled, which adds to their inefficiency.

• Devices that are used for lighting are also very inefficient.

Energy Systems and Strategies

• In modern societies, energy is usually not used in one or two simple steps• For instance making a toast requires many steps. Farmers must first plant,

fertilize, and harvest grain. The grain must then be shipped, stored, ground, and the resulting flour hauled to a bakery. At the bakery, the flour is made into dough that is baked into a loaf, packaged, and then shipped to a supermarket. Consumers buy the loaves and take them home to make toast. • The energy to power the farm equipment, trucks, and cars and the

electricity to power the toaster are also produced in many step systems.• A system, in this case, is a series of steps designed to produce a useful

product or service.