Resumo de About Energy Part 2

11. What are some examples of Energy Transformation?

a) When you are out in the sunshine (sunlight) you feel warm because the solar radiant energy excites the molecules of your skin and so creates heat there. b) When you do physical exercise the chemical energy stored in the carbohydrate, fat, and other molecules in the cells of your body is converted to energy of motion. c) When coasting downhill on your bicycle the potential energy you possess because of your distance from the center of Earth becomes converted to kinetic energy and your speed increases until you reach the bottom of the hill.

12. What is the relationship between change (meaning 'work') and energy?

Change - or work - in all systems and processes in both the physical and biological worlds relies on the availability of energy. Heat energy within the Earth creates change through the activity of volcanoes and distortion of the Earth's crust. Chemical energy creates change by being the basis of metabolism in plant and animal life. Energy stored in dead vegetable matter ultimately (as fossil fuel) is a source of electrical power which is necessary for work done by electrical equipment of all kinds.

13. Is energy involved in changes of physical state?

Yes. When water, for example, changes its physical state from one in which the molecules are tightly packed together to one in which they are loosely packed (as from ice to water) energy is necessary to effect the change. The amount of energy needed for one gram of ice to change to water is 80 calories (335 joules). To change one gram of solid ice to water vapor requires 680 calories (2843 joules) of energy.

14. How is energy involved when water changes from its gaseous (water vapor) state to its liquid state?

In this situation loosely packed molecules of water vapor release energy as they become more closely packed together to become liquid water. This is why a burn from steam from boiling water in a tea kettle can be more severe than a burn from the hot water in the kettle. As it touches the skin the hot steam not only heats up the skin because it is hot but, in addition, as it changes from steam to hot water its molecules release extra heat energy this increasing the severity of the burn.

15. How can energy be measured?

In animals and plants the amount of stored energy can be measured using a 'bomb calorimeter'. In this device a sample of plant or animal material can be converted to heat energy which is measured as an increase in temperature. This increase in temperature is converted to an energy measurement. (Energy is measured in joules or in calories.)

16. What units are used in the measurement of energy?

For example, the amount of energy needed to move one kilogram of mass a distance of one meter in one second-per-second (one second squared) is called a Newton (named for Isaac Newton an English scientist 1642-1727). Energy is also commonly measured in units called gram calories. One gram-calorie - usually spoken of simply as a calorie with a lower case 'c', is the amount of energy needed to raise the temperature of one gram of water from 14.5 degrees Celsius to 15.5 degrees Celsius.

17. Are food Calories the same as other calories?

No. The term Calorie used in relation to food energy means a kilocalorie and one Calorie (upper case 'C') or kilocalorie is equal to 1,000 gram-calories. In many parts of the world (but not yet in the US) a different unit is now used for food energy. This unit is the 'joule'.

18. Is food energy always measured in calories?

No. The calorie (gram-calorie) and Calorie (kilocalorie) are being replaced by the joule and kilojoule. Here are some equivalents:

1 Calorie (kilocalorie) = 1,000 calories

1 Calorie (kilocalorie) = 4184 joules

1 Calorie (kilocalorie) = 4.184 kilojoules

1 kilojoule = 0.239 kilocalories (Calories).19. Does all of the Sun's radiated energy reach Earth?

No. The Sun is a spherical object and it radiates energy equally in all directions. Earth intercepts only a tiny fraction of the total radiation emitted by the Sun. However, this tiny fraction is actually an enormous amount of energy. The amount of solar energy intercepted by Earth in one minute is approximately equal to the total electrical energy artificially generated on Earth in an entire year.

20. Does Earth receive the same amount of solar energy all the time?

No. Earth intercepts the greatest amount of solar radiation in January when its orbit brings it closest to the Sun; and the least amount in July when its orbit takes it farthest from the Sun. This difference amounts to about 7 percent.

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