The unit “Energy in a Clean Environment” is designed for a ninth grade integrated science class. The topics of energy, work and power will be covered in this unit. The class will begin by covering what energy is and its various forms. The relationship of work and energy will then be discussed. We continue by correlating the units calories, joules and watts used to describe energy, work and power. The first two activities “Heat Energy Calculation Lab” and “Personal Power Lab” are inquiry-based labs used to help the student created an understanding of what the joule and the watt are. The student will be able to take these ideas out of the classroom into real life applications such as reading their energy bill and understanding wattage in home appliances. A discussion will follow on our current energy use and acquisition and conclude with the issues of alternative and sustainable energy sources while looking at each sources advantages and disadvantages. At this point in the unit a field trip to a local power company is used to justify what the class has been learning. It will help to create relevance to the subject of energy. The final unit activity consists of a group research project and presentation on renewable energy sources. In this presentation the students pay particular attention to the efficiency of each alternative energy source as well as what limitations exist in terms of extracting the useable energy. The student will be able to determine which energy source will be most effective to the economy and the environment in the future. It is suggested that the teacher prepare their own model presentation of fossil fuels following the guide lines of the presentation prior to the field trip to enhance the understanding of how heavily we rely on fossil fuels and their role in electrical energy production.
After completing this unit students will:
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1. Distinguish between potential and kinetic energy
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2. Identify and describe different forms of energy
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3. Explain how heat is a form of energy in transfer
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4. Define units for describing energy, such as the calorie and joules.
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5. Explain how power is used to describe work done over time.
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6. Recognize that some energy is wasted in energy conversion.
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7. Demonstrate and understanding of renewable and nonrenewable sources of energy
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8. Explain why the supply of fossil fuels is finite and discuss the deleterious environmental effects of fossil fuel use.
I. Discussion on Energy and its Various Form
A. Introduction
The survival of human beings has been predicated on our artful manipulation of energy. When fire was first used to radiate heat this harnessing of energy began. The use of energy has been important to food supplies, industrialization and in the improvement of the quality of life. The use of energy relies on the availability of resources and the technological skills in converting the resources to useful heat and work.1
The U.S. industrial society is based on energy and its ability to do work. The success of an industrial society, its economical growth, the quality of life of its people and its impact on other societies depends largely on the quantities and kinds of energy resources it exploits and on the efficiency of its systems for converting potential energy into work and heat.1 Therefore our industrialized society is characterized by its consumption of energy. This consumption is currently based on its dependence of fossil fuels; solar energy stored potentially as coal, oil and natural gas rather than renewable sources such as wind, hydro, nuclear, solar, geothermal and biomass.
During the 1970’s and early 1980’s there was an increase in the price of oil. This was largely due to the global reductions in oil supplies as a result of the OPEC oil embargo in 1973 and the Iranian hostage crisis in 1979. As a result there was an increasing interest in energy policy and energy conservation nationwide. As the price of oil increased during this period both government and private sectors scurried for the development of renewable energy sources such as solar, wind, geothermal and biomass. When the oil prices fell back to reasonable levels toward the late 1980’s national commitment to renewable energies subsided. The prices of these alternative sources were too high for government and consumers to invest in and the inexpensive fossil fuels were again the primary source of energy.1
In recent years there has been a growing interest in renewable energy due to environmental health and political concerns. Fossil fuel use correlates to air pollution especially in urban areas, which is a growing health concern while acid rain and global warming continues to evoke debate. Another growing concern is the current Middle Eastern situation due to the U.S. dependence on foreign oil.
The youth are the future that is why it is crucial for the education of our future engineers and policy makers in the laws of thermodynamics and alternative energy sources. Public policy issues concerning energy have direct correlations with the economy. To solidify wise public policy citizens and legislators must have an understanding about energy sources and be able to apply this knowledge to economic concepts in their analysis of energy issues.
What are energy, work and power?
Energy cannot be created or destroyed but it is converted from one form to another. Everything that occurs in the universe revolves around energy. Heat, light, sound, and electricity are all forms of energy. There are two major categories of energy: kinetic and potential energy. Potential energy is stored energy, energy waiting to be used. Kinetic energy is energy in motion. The energy of a moving object or the movements of light energy are both examples of kinetic energy. Heat energy, the motion of rapidly moving and colliding molecules is also an example. The most important potential energy used by our developing societies is chemical energy, which is found in our foods and fuels.
There are limiting laws of energy which describe what can and cannot happen during interactions of energy. The laws of thermodynamics are stated as:
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1. Energy can neither be created nor destroyed.
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2. No device can be constructed which operating in a cycle accomplishes only the extraction of heat energy from a reservoir and its complete conversion to mechanical energy (work).
Energy can be defined as the capacity to do work. Work is defined as any interaction between a system and its surrounding that has or could have as a sole effect in either the system or the surroundings the raising of a weight.2 Work is a measurable amount of energy which is converted from one form to another. Therefore work represents a change in energy from one form to another.
An example of how the concept of energy can be used to do work is the Hero engine described in 150 B.C. by a Greek, Hero of Alexandria. Water is placed into a sphere and heated until it boils. When the steam escapes through nozzles it results in forces that cause it to spin. This was the first example of a properly designed steam engine and jet engine and shows that heat can be transformed into work. Another example is rubbing your hands together. Mechanical work, that is force applied through a distance, is transferred to your hands and you feel the result as a rise in temperature. Therefore heat is produced by work and that heat can be used to cause a force to move through a distance. Heat and work are just different forms of the same thing and can be converted into one another.
Light can cause an object to heat up and the hot object can be made to do work. Therefore light can be converted into work. Electricity flowing through a wire causes it to heat up and that heat can be made to do work. We can also spin a magnet in a coil of wire (by applying a force through a distance) and cause electricity to flow through the wire. We can use that electricity to light a light bulb or heat up wires or boil water in our Hero engine so that it spins around.
In all of these examples we are converting the quantity that we call energy from one form into another. When one part of the universe loses energy another part gains energy in the same amount. Therefore
Energy
is anything that can do
Work
or cause a change.
In comparing the amount of energy stored in foods and fuels the unit called a calorie is used. One calorie is the amount of energy needed to raise the temperature of 1 g of water by 1ºC. One thousand calories equals a kilocalorie or the more standard food Calorie. This is the amount of heat energy, which will raise the temperature of 1 kg of water 1ºC.
The unit of measurement of work combines the unit of force, Newton, with the unit of distance, meter, and the resulting unit of work is the Newton-meter. One joule of work is done when a force of 1 N is exerted over a distance of 1 m. In James Joule’s original experiments of a paddle wheel he was able to show that 1 joule is equal to 4186 Calories. 4
The rate at which work is done is called
Power
and can be calculated by dividing work by time. The SI unit for power are (N)?(m)/s or J/s. The units of power are given the name Watt (W) after the inventor of the first practical steam engine James Watt.
Watt calculated the power of his machines in terms of how fast horses could do work so that people of his time during the 1700’s could understand them. Watt’s observations showed that a horse could lift 550 pounds to a height of 1 foot in one second. That rate of doing work is called a horsepower (HP) and is still used as a standard today in the United States. One HP is equal to about 746 W.
A 100 Watt light bulb uses energy at a rate that could lift 100 N of weight to a height of 1 m each second. That’s about 13 pounds raised to a height of a little more than 3 feet each second. If you run a 60 W bulb for an hour it brings an awful lot of energy into your house. If we look at work as energy then the calculation looks like this.
The amount of electrical energy used over a given time is measured in a unit called the watt. We can use the watt to compare the rates at which different electrical devices use energy. Electricity companies provide us with a lot of energy for a pretty low price. These companies are often called power companies however they are really energy companies. They convert chemical energy in coal, oil, gas, or nuclear energy from the nuclei of uranium atoms into electrical energy for us to consume as light, heat, or some sort of electromagnetic energy.
