1. Chapter 15 Energy

2. Cow Power Without a supply of energy to run our millions of machines, society as we know it would cease to exist! Because of our reliance on fossil fuels, supplies of coal, gas, and oil are dwindling. But the ability to convert from one form to another may yet save our way of life, An unusual source of energy may save us upto 300,000 barrels of oil a year- cow power!! In a mutualistic relationship, owners of cow feedlot and 250,000 head of cattle are supplying a power plant in California with about 1500 metric tons of cow manure a day. Once manure is scraped out of the feedlots, it is piled in long, wide berms, sprinkled with line, and dried for later use. The manure is fed into the plants combustor and is passed down a series of platforms or hearths to dry. Escaping gases are recaptured and burned, reducing emissions from the plant. The hot manure is then burned, and the burning manure heats up an adjacent boiler to produce steam. The steam turns a turbine, which turns a generator to produce electricity. The electricity is then sold to a power company. Cow manure is readily available, easily obtained, and cheap source of fuel for the production of electricity. Thank a cow - it may be providing more than just a glass of milk in the near future.

3. Section 1 Energy and Its Forms

4. Key Concepts How are energy and work related? What factors does the kinetic energy of an object depend on? How is gravitational potential energy determined? What are the major forms of energy?

5. Energy and Work Energy is the ability to do work. In other words, energy is transferred by a force moving an object through a distance. When work is done on an object, energy is transferred to that object. Both work and energy are typically measured in joules (J).

6. Kinetic Energy The energy of motion The kinetic energy of any moving object depends upon its mass and speed. Formula: Kinetic energy (KE)= 1 2 mv 2 m= Mass v= Velocity

7. A 70.0-kilogram man is walking at a speed of 2.0 m/s. What is his kinetic energy?

8. A 1400-kilogram car is moving at a speed of 25 m/s. How much kinetic energy does the car have?

9. A 50.0-kilogram cheetah has a kinetic energy of 18,000 J. How fast is the cheetah running? (Hint: Rearrange the equation to solve for v.)

10. Kinetic Energy Notice that doubling the mass in the formula would double the kinetic energy. However, doubling the speed would quadruple the kinetic energy, since kinetic energy is proportional to the square of an object’s speed.

11. Potential Energy energy that is stored as a result of position or shape. Two forms of potential energy are gravitational energy and elastic potential energy. When this musician pulls the string of her cello to one side, the string is stretched and gains potential energy.

12. Gravitational Potential Energy Potential energy that depends upon an object’s height An object’s gravitational potential energy depends on its mass, its height, and the acceleration due to gravity. This diver has gravitational potential energy as she stands at the end of a diving board.

13. Gravitational Potential Energy Formula: Potential energy (PE) = mgh m= mass g= gravity h= hieght The acceleration due to gravity, g, has a value in SI units of 9.8 m/s 2 on Earth.

14. Elastic Potential Energy The potential energy of an object that is stretched or compressed Something is said to be elastic if it springs back to its original shape after it is stretched or compressed. A compressed bicycle shock absorber and a wound-up toy robot both have elastic potential energy.

15. Forms of Energy All energy can be considered to be kinetic energy, potential energy, or the energy in fields such as those produced by electromagnetic waves. The major forms of energy are mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy, and nuclear energy.

16. Mechanical Energy The energy associated with the motion and position of everyday objects Mechanical energy is not limited to machines. Mechanical energy is the sum of an object’s potential energy and kinetic energy Speeding trains, bouncing balls, and sprinting athletes all have mechanical energy.

17. Thermal Energy Almost all of the matter around you contains atoms. The total potential and kinetic energy of all the microscopic particles in an object make up its thermal energy When an object’s atoms move faster, its thermal energy increases and the object becomes warmer Energy occurs in many forms. This molten metal is extremely hot. It contains a Great deal of thermal energy

18. Chemical Energy the energy stored in chemical bonds When bonds are broken, the released energy can do work. All chemical compounds, including fuels such as coal and gasoline, store energy. This family is using the chemical energy of burning wood to produce thermal energy for heating marshmallows.

19. Electrical Energy the energy associated with electric charges. Electric charges can exert forces that do work. Electrical energy also occurs in nature. CD players, flashlights, and calculators. Lightning bolts transfer electric charge.

20. Electromagnetic Energy a form of energy that travels through space in the form of waves. Visible light and X-rays Because electromagnetic waves can travel long distances through air and space, they are often used for communication. Galaxies are giant structures in space that typically contain billions of stars. The stars give off enormous amounts of electromagnetic energy

21. Nuclear Energy The nucleus of an atom is held together by strong and weak nuclear forces, which can store an enormous amount of potential energy. The energy stored in atomic nuclei is known as nuclear energy. Nuclear fission is a process that releases energy by splitting nuclei apart. Nuclear fusion, releases energy when less massive nuclei combine to form a more massive nucleus.

22. Reviewing Concepts 1. Describe the relationship between work and energy. 2. How is the kinetic energy of an object determined? 3. What factors determine the gravitational potential energy of an object? 4. Give an example of each of the major forms of energy. 5. When you heat a pot of water over a flame, what form of energy is added to the water?