In Most Energy Transformations, Some Energy Is Always Changed Into What?

Learning Objectives

By the end of this section, you will exist able to:

Describe the stardom between renewable and nonrenewable energy sources.
Explain why the inevitable conversion of energy to less useful forms makes information technology necessary to conserve free energy resources.

Energy is an important ingredient in all phases of social club. We live in a very interdependent globe, and access to acceptable and reliable energy resources is crucial for economic growth and for maintaining the quality of our lives. Only current levels of free energy consumption and production are non sustainable. About 40% of the world's free energy comes from oil, and much of that goes to transportation uses. Oil prices are dependent equally much upon new (or foreseen) discoveries equally they are upon political events and situations around the world. The U.South., with 4.5% of the world's population, consumes 24% of the world's oil production per twelvemonth; 66% of that oil is imported!

Renewable and Nonrenewable Energy Sources

The master energy resources used in the world are shown in Effigy 1. The fuel mix has inverse over the years but at present is dominated by oil, although natural gas and solar contributions are increasing. Renewable forms of energy are those sources that cannot exist used upwardly, such every bit water, current of air, solar, and biomass. Well-nigh 85% of our energy comes from nonrenewable fossil fuels—oil, natural gas, coal. The likelihood of a link between global warming and fossil fuel use, with its production of carbon dioxide through combustion, has made, in the optics of many scientists, a shift to non-fossil fuels of utmost importance—merely it will non exist easy.

Figure 1. World free energy consumption by source, in billions of kilowatt-hours: 2006. (credit: KVDP)

The World's Growing Energy Needs

Earth free energy consumption continues to rise, especially in the developing countries. (Run into Figure two.) Global need for energy has tripled in the past 50 years and might triple again in the next 30 years. While much of this growth will come from the apace booming economies of Prc and India, many of the adult countries, especially those in Europe, are hoping to run across their free energy needs by expanding the utilise of renewable sources. Although presently only a small percent, renewable energy is growing very fast, especially wind energy. For instance, Germany plans to come across twenty% of its electricity and 10% of its overall energy needs with renewable resources past the year 2020. (See Figure 3.) Energy is a key constraint in the rapid economic growth of China and Bharat. In 2003, China surpassed Nippon as the globe'south second largest consumer of oil. However, over one/3 of this is imported. Unlike well-nigh Western countries, coal dominates the commercial energy resource of Mainland china, accounting for 2/3 of its energy consumption. In 2009 Prc surpassed the The states as the largest generator of CO₂. In Republic of india, the master energy resources are biomass (wood and dung) and coal. Half of India'due south oil is imported. Most 70% of India'south electricity is generated by highly polluting coal. Yet there are sizeable strides being made in renewable energy. Bharat has a rapidly growing wind energy base, and it has the largest solar cooking plan in the world.

Figure two. Past and projected world energy use (source: Based on data from U.S. Free energy Information Administration, 2011)

Solar cell arrays lined up in a field.

Figure three. Solar cell arrays at a ability plant in Steindorf, Germany (credit: Michael Betke, Flickr)

Table 1 displays the 2006 commercial energy mix by country for some of the prime energy users in the world. While non-renewable sources dominate, some countries go a sizeable percentage of their electricity from renewable resources. For instance, about 67% of New Zealand's electricity demand is met by hydroelectric. Simply x% of the U.S. electricity is generated by renewable resources, primarily hydroelectric. It is difficult to determine total contributions of renewable free energy in some countries with a large rural population, so these percentages in this table are left blank.

Table i. Energy Consumption—Selected Countries (2006)
Country	Consumption, in EJ (ten¹⁸ J)	Oil	Natural Gas	Coal	Nuclear	Hydro	Other Renewables	Electricity Employ per capita (kWh/yr)	Free energy Use per capita (GJ/yr)
Australia	5.iv	34%	17%	44%	0%	3%	1%	10000	260
Brazil	9.6	48%	7%	v%	1%	35%	2%	2000	50
China	63	22%	3%	69%	1%	half dozen%		1500	35
Egypt	2.4	50%	41%	1%	0%	6%		990	32
Federal republic of germany	16	37%	24%	24%	eleven%	1%	three%	6400	173
India	fifteen	34%	seven%	52%	1%	5%		470	thirteen
Indonesia	4.9	51%	26%	16%	0%	two%	3%	420	22
Nippon	24	48%	14%	21%	12%	4%	ane%	7100	176
New Zealand	0.44	32%	26%	6%	0%	11%	19%	8500	102
Russian federation	31	19%	53%	16%	v%	6%		5700	202
U.Southward.	105	40%	23%	22%	8%	3%	1%	12500	340
World	432	39%	23%	24%	6%	6%	two%	2600	71

Energy and Economic Well-being

The last two columns in this tabular array examine the free energy and electricity use per capita. Economical well-existence is dependent upon energy utilise, and in most countries higher standards of living, as measured by Gdp (gross domestic product) per capita, are matched past higher levels of energy consumption per capita. This is borne out in Figure 4. Increased efficiency of free energy utilise will change this dependency. A global problem is balancing free energy resource development against the harmful effects upon the environs in its extraction and utilize.

A scatter plot of power consumption per capita versus G D P per capita for various countries. Power consumption in kilowatt per capita is shown along the horizontal axis and G D P per capita is show along the vertical axis.

Effigy iv. Power consumption per capita versus GDP per capita for various countries. Note the increase in energy usage with increasing GDP. (2007, credit: Frank van Mierlo, Wikimedia Commons)

Conserving Energy

As we stop this affiliate on energy and work, it is relevant to depict some distinctions between two sometimes misunderstood terms in the area of energy use. As has been mentioned elsewhere, the "police of the conservation of energy" is a very useful principle in analyzing physical processes. It is a statement that cannot be proven from basic principles, simply is a very good bookkeeping device, and no exceptions take ever been found. It states that the total amount of energy in an isolated organization will always remain constant. Related to this principle, but remarkably dissimilar from it, is the important philosophy of energy conservation. This concept has to exercise with seeking to subtract the amount of energy used by an private or group through (1) reduced activities (east.g., turning downwardly thermostats, driving fewer kilometers) and/or (two) increasing conversion efficiencies in the performance of a particular task—such every bit developing and using more efficient room heaters, cars that take greater miles-per-gallon ratings, energy-efficient compact fluorescent lights, etc.

Since energy in an isolated system is not destroyed or created or generated, one might wonder why we demand to exist concerned almost our energy resources, since energy is a conserved quantity. The problem is that the final outcome of most energy transformations is waste heat transfer to the environment and conversion to energy forms no longer useful for doing piece of work. To land it in another way, the potential for energy to produce useful work has been "degraded" in the energy transformation. (This will be discussed in more particular in Thermodynamics.)

Section Summary

The relative apply of different fuels to provide energy has inverse over the years, but fuel use is currently dominated by oil, although natural gas and solar contributions are increasing.
Although non-renewable sources dominate, some countries encounter a sizeable percentage of their electricity needs from renewable resource.
The The states obtains only nigh 10% of its energy from renewable sources, mostly hydroelectric ability.
Economical well-being is dependent upon energy utilize, and in well-nigh countries higher standards of living, as measured by GDP (Gross domestic product) per capita, are matched by higher levels of energy consumption per capita.
Fifty-fifty though, in accordance with the constabulary of conservation of energy, energy can never be created or destroyed, energy that can be used to practice piece of work is always partly converted to less useful forms, such as waste heat to the surround, in all of our uses of energy for practical purposes.

Conceptual Questions

What is the difference between energy conservation and the police force of conservation of energy? Give some examples of each.
If the efficiency of a coal-fired electrical generating plant is 35%, then what exercise we mean when we say that energy is a conserved quantity?

Problems & Exercises

Integrated Concepts.(a) Calculate the force the woman in Figure 5 exerts to do a push-upwardly at constant speed, taking all data to be known to three digits. (b) How much work does she do if her center of mass rises 0.240 k? (c) What is her useful ability output if she does 25 push-ups in 1 min? (Should work washed lowering her torso be included? Run across the word of useful work in Work, Free energy, and Power in Humans.

Figure v. Forces involved in doing push button-ups. The woman's weight acts as a force exerted downward on her center of gravity (CG).
Integrated Concepts.A 75.0-kg cantankerous-country skier is climbing a 3.0º slope at a constant speed of 2.00 m/southward and encounters air resistance of 25.0 N. Find his power output for piece of work done against the gravitational strength and air resistance. (b) What average forcefulness does he exert backward on the snow to accomplish this? (c) If he continues to exert this forcefulness and to experience the same air resistance when he reaches a level expanse, how long volition it take him to reach a velocity of ten.0 yard/s?
Integrated Concepts.The 70.0-kg swimmer in Figure 6 starts a race with an initial velocity of 1.25 m/south and exerts an boilerplate strength of 80.0 Due north backward with his artillery during each i.80 m long stroke. (a) What is his initial acceleration if h2o resistance is 45.0 N? (b) What is the subsequent average resistance forcefulness from the water during the five.00 s information technology takes him to reach his elevation velocity of ii.50 one thousand/s? (c) Discuss whether h2o resistance seems to increment linearly with velocity.

Figure six.
Integrated Concepts.A toy gun uses a bound with a forcefulness abiding of 300 North/m to propel a ten.0-g steel ball. If the leap is compressed 7.00 cm and friction is negligible: (a) How much force is needed to compress the leap? (b) To what maximum tiptop can the ball be shot? (c) At what angles above the horizontal may a child aim to striking a target 3.00 chiliad away at the same height as the gun? (d) What is the gun's maximum range on level ground?
Integrated Concepts.(a) What force must exist supplied by an elevator cable to produce an acceleration of 0.800 m/due south² against a 200-N frictional force, if the mass of the loaded elevator is 1500 kg? (b) How much work is done by the cable in lifting the lift 20.0 m? (c) What is the last speed of the elevator if it starts from balance? (d) How much work went into thermal energy?
Unreasonable Results.A car advertisement claims that its 900-kg motorcar accelerated from rest to 30.0 m/due south and drove 100 km, gaining 3.00 km in distance, on one.0 gal of gasoline. The average force of friction including air resistance was 700 North. Assume all values are known to three significant figures. (a) Calculate the machine's efficiency. (b) What is unreasonable about the outcome? (c) Which premise is unreasonable, or which premises are inconsistent?
Unreasonable Results. Trunk fatty is metabolized, supplying 9.xxx kcal/grand, when dietary intake is less than needed to fuel metabolism. The manufacturers of an exercise bicycle claim that you tin lose 0.500 kg of fatty per mean solar day past vigorously exercising for 2.00 h per day on their machine. (a) How many kcal are supplied past the metabolization of 0.500 kg of fat? (b) Calculate the kcal/min that you would take to utilize to metabolize fat at the rate of 0.500 kg in 2.00 h. (c) What is unreasonable about the results? (d) Which premise is unreasonable, or which premises are inconsistent?
Construct Your Ain Problem.Consider a person climbing and descending stairs. Construct a problem in which yous calculate the long-term rate at which stairs can be climbed because the mass of the person, his power to generate power with his legs, and the height of a single stair pace. Too consider why the same person can descend stairs at a faster rate for a nearly unlimited time in spite of the fact that very similar forces are exerted going down as going up. (This points to a fundamentally different process for descending versus climbing stairs.)
Construct Your Own Trouble.Consider humans generating electricity by pedaling a device similar to a stationary bicycle. Construct a trouble in which you make up one's mind the number of people information technology would accept to replace a large electrical generation facility. Amidst the things to consider are the power output that is reasonable using the legs, rest time, and the need for electricity 24 hours per day. Discuss the practical implications of your results.
Integrated Concepts.A 105-kg basketball player crouches down 0.400 chiliad while waiting to jump. After exerting a force on the flooring through this 0.400 m, his feet leave the floor and his center of gravity rises 0.950 m above its normal standing erect position. (a) Using energy considerations, calculate his velocity when he leaves the floor. (b) What average strength did he exert on the floor? (Practice not neglect the force to support his weight besides as that to accelerate him.) (c) What was his power output during the dispatch phase?

Glossary

renewable forms of energy: those sources that cannot be used upward, such as water, current of air, solar, and biomass

fossil fuels: oil, natural gas, and coal

Selected Solutions to Problems & Exercises

1. (a) 294 North; (b) 118 J; (c) 49.0 W

3. (a) 0.500 m/s²; (b) 62.five North; (c) Assuming the acceleration of the swimmer decreases linearly with fourth dimension over the 5.00 s interval, the frictional force must therefore be increasing linearly with fourth dimension, since f= F− ma. If the dispatch decreases linearly with time, the velocity will comprise a term dependent on time squared (t ²). Therefore, the water resistance will not depend linearly on the velocity.

5. (a) 16.i × xⁱⁱⁱ N; (b) 3.22 × 10^v J; (c) v.66 m/southward; (d) 4.00 kJ

seven. (a) 4.65 × 10³ kcal; (b) 38.viii kcal/min; (c) This power output is higher than the highest value on Table two in Piece of work, Energy, and Power in Humans, which is about 35 kcal/min (corresponding to 2415 watts) for sprinting; (d) It would be impossible to maintain this power output for two hours (imagine sprinting for 2 hours!).

10. (a) 4.32 m/southward; (b) 3.47 × 10³ N; (c) eight.93 kW