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Energy

Energy. Chapter 4 Sections 1 & 2. Chp 4 Energy. S1- The Nature of Energy slides 3-18 S2- Conservation of Energy slides 19-. Section 1- The Nature of Energy. What You’ll Learn: The different forms of energy How energy can be stored. What is Energy?. All changes involve energy.

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Energy

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  1. Energy Chapter 4 Sections 1 & 2

  2. Chp 4 Energy • S1- The Nature of Energy slides 3-18 • S2- Conservation of Energy slides 19-

  3. Section 1- The Nature of Energy • What You’ll Learn: • The different forms of energy • How energy can be stored

  4. What is Energy? • All changes involve energy. • Light bulbs heat air • Wind blows trees & leaves • You breathe, blink, move • Moving baseball hits a window…

  5. Does change require energy? • Energy is the ability to cause change. • Anything that causes change must have energy.

  6. What are some different forms of energy? • Electrical- light bulb uses it • Chemical- stored in food • Radiant- comes from Sun • Thermal- heat energy from the movement of atoms & molecules

  7. How is energy like money? • You can change it into different forms. • Energy is the same no matter what form it is in.

  8. Kinetic Energy • Kinetic energy is the energy a moving object has because of its motion. • KE depends on the object’s mass & speed. • KE measured in unit joules.

  9. Kinetic Energy • KE (j)= ½ mass (kg) X [speed (m/s)]2 or • KE= ½ mv2 • Energy is measured using the SI unit called the joule. • 1J= KE of a baseball dropped from 0.5 m

  10. Kinetic Energy • A jogger whose mass is 60 kg is moving at a speed of 3 m/s. • KE= ½ mv2 =1/2 (60 kg)(3m/s)2 =1/2 (60 kg) (9 m2/s2) • = 30∙9 kg∙m2/s2 • = 270 kg∙m2/s2 • The kinetic energy of the jogger is 270 J.

  11. Potential Energy • Objects at rest have stored energy. • Stored energy due to position is called potential energy. • PE can change to KE when position changes.

  12. What is elastic potential energy? • Elastic PE is stored by an object that can stretch or shrink like a rubber band or a spring. • EPE can change to KE when released.

  13. What is chemical potential energy? • Chemical PE is stored in chemical bonds in food and in hydrocarbons like natural gas. • The energy is released when the substance is burned.

  14. What is gravitational potential energy? • Anything that can fall has stored energy. • Gravitational potential energy (GPE) is energy that is stored by objects that are above Earth’s surface. • It depends on mass & height.

  15. What is gravitational potential energy? • GPE= mass (kg) X acceleration of gravity (m/s2) X height (m) or GPE=mgh, where g= 9.8 m/s2 • A ceiling fan has a mass of 7 kg & is 4 m high. • GPE= mgh = (7 kg)(9.8 m/s2)(4m) =274 kg m2/s2 or 274 joules.

  16. How is potential energy stored?

  17. How does GPE change? • The acceleration of gravity is a constant or 9.8 m/s2. • The other two factors mass (m) and height (m) are variables that can change.

  18. What does GPE change into? • GPE changes into kinetic energy as height changes. • If mass is increased, GPE also increases so that when the object falls it converts into more KE.

  19. Section 2- Conservation of Energy • What You’ll Learn: • How energy can be changed from one form to another • How energy is conserved

  20. Changing Forms of Energy • Many situations involve changing energy from one form to another. • Cars use fuel for energy • Bodies digest food for energy • Sun warming Earth, etc.

  21. How can electrical energy change? “A Compact Fluorescent Light produces light when electricity is passed through a gas sealed in a glass tube, creating UV rays which react with a phosphor coating on the inside of the glass tube. CFLs use less power, release less heat, and last a lot longer than an incandescent light bulb.” <www.torontohydro.com/>

  22. How can electrical energy change? In other words, electricity is changed to light and thermal energy or heat. <www.torontohydro.com/>

  23. How can chemical energy change? • Chemical energy can be changed into KE. In an engine, an electrical spark causes a small amount of fuel to burn becoming thermal energy. The gases expand causing parts of the car to move (KE). <http://www.geocities.com/MotorCity>

  24. Do all energy changes result in motion? • Not all changes in energy result in motion that can be seen. • Nor do they all result in sound, heat, or light. • EX. Green plants change sunlight to CE; when you eat the plant the CPE is changed to other forms of energy.

  25. Changes Between Kinetic & Potential Energy • Mechanical energy is the total amount of potential & kinetic energy in a system. • The ME of a rubber band is the total of its PE + KE at any one time. • ME comes from where an object is & the movement of the object.

  26. Does the mechanical energy of an object change? • These apples have GPE; as they fall they lose height thus reducing GPE & raising KE. However, the total ME remains the same. <http://farm2.static.flickr.com/>

  27. How does energy change in projectile motion? • A ball moves through the air in a curved path. • As the ball rises so does its GPE but its KE goes down; as it falls the opposite occurs. <http://ca7science.wikispaces.com/space/showimage/golf3.gif>

  28. What happens to energy during a swing? • Energy is constantly changing during a ride on a swing. The push is KE; at the top of the path KE is low but GPH is high. Going down the speed increases as GPE changes to KE. As you swing KE & PE are constantly changing back & forth.

  29. The Law of Conservation of Energy • Although KE & PE are always changing, mechanical energy always stays the same. • No energy is destroyed; instead it is conserved. • The Law states that energy is neither created nor destroyed.

  30. Is energy always conserved? • There are times when it seems energy is not conserved. • When you are coasting along on your bike you eventually must pedal to keep going. • Why is this?

  31. How does friction affect energy? • Friction and air resistance create thermal energy. • The total amount of mechanical energy remains the same, it just changes form.

  32. Where does the Sun get its energy? • Nuclear fusion is the reaction that takes places when nuclei join together. It changes PE of a small amount of mass into huge amounts of energy. <http://quest.arc.nasa.gov/eclipse99/images/SunActiv_sunCutaway.gif>

  33. What is nuclear fission? • In nuclear fission, the nucleus is broken apart. Once again mass is turned into energy, but energy is also conserved. <http://www.oxfordreference.com/media/images/31908_0.jpg>

  34. Energy & the Human Body • In order to move your body changes stored PE to KE. It also changes it to thermal energy to maintain body temp. • The total amount of mass & energy do not change. <http://media.hcpss.org/newcode/electronicresources/>

  35. How does your body store & use energy? • The PE stored in your body as fat and other chemical compounds is the fuel for processes such as the beating of your heart, digesting of food, & moving muscles. <http://museumvictoria.com.au/>

  36. What are calories? • The food Calorie (C) is a unit nutritionists use to measure how much energy foods contain. • One Calorie = 4,184 J • These Calories produce the energy your body’s cells need to function.

  37. Calories Used in 1 Hour

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