1. Varying degrees of conversion in real systems

Although the total amount of energy in an isolated system remains unchanged, there may be a great difference in the 6 ... of different forms of energy. Many forms of energy, in theory, can be transformed completely into work or into other forms of energy. This is true for mechanical energy and electrical energy. The random motions of constituent parts of a material associated with thermal energy, however, represent energy that is not available completely for conversion into directed energy.

The French engineer Sadi Carnot described (in 1824) a theoretical power cycle of maximum 7 ... for converting thermal into mechanical energy. He demonstrated that this efficiency is determined by the 8 ... of the temperatures at which heat energy is added and waste heat is given off during the cycle. A practical engine operating on the Carnot cycle has never been devised, but the Carnot cycle determines the maximum efficiency of thermal energy conversion into any form of directed energy. The Carnot criterion renders 100 percent efficiency impossible for all heat engines. In effect, it constitutes the basis for what is now the second law of thermodynamics.

I. Use the terms to fill in the gaps (1 – 8): Conservative, quality, conservation, magnitude, potential, efficiency, kinetic, velocity, speed.

II. Decide whether the statements are true or false:

1. To show how energy is converted you should throw the ball horizontally.

2. The kinetic energy E_k of the ball increased steadily at the highest point.

3. Potential energy is stored in hidden form and can be drawn upon to do work.

4. In the ideal system we consider the friction of the air.

5. As the ball falls back to the ground level, gravitational potential energy is converted back into kinetic energy.

6. Although the total amount of energy in an isolated system remains unchanged, there may be a great difference in the quantity of energy.

7. A practical engine operating on the Carnot cycle has never been created.

8. The Carnot cycle determines the maximum efficiency of conversion of any type of energy into any form of directed energy.

III. Think of the following:

1. Explain what the basic difference between kinetic and potential energy is.

2. Why does the ball stay at rest at the highest point?

3. What does the law of conservation of energy state?

4. What is a conservative system? Why is the system described called a conservative one? Can you give any more examples of conservative systems?

5. In what way are the real and the ideal systems different?

6. Why is the example with the ball supposed to be idealized?

7. According to Carnot, what is efficiency determined by?

IV. Summarize the article in 7 – 8 sentences.

V. Additional questions:

1. What is understood by mechanical energy? What are the conditions for its being constant?

2. Describe how energy is converted on the example of water behind a dam flowing to lower levels through turbines (hydroelectricity).

3. Why is the mechanical energy of the Earth-Moon system nearly constant?

4. How does the energy change back and forth when you are riding a roller-coaster? What energy prevails when you are:

• at the top

• as you roll down the track

• you go round the loop

• you go over the bump