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5.2 – CONSERVATION OF ENERGY OBJECTIVES • Describe how energy can be transformed from one form to another. • Explain how the mechanical energy of system is the sum of the potential and the kinetic energies. • Discuss the law of conservation of energy. CHANGING FORMS OF ENERGY • Light bulb Light & Heat • Electrical Radiant & Thermal CHANGING FORMS OF ENERGY • Fuel Moving Car • Chemical Potential Thermal • Electric spark ignites fuel • Thermal Kinetic • Gases expand and move parts of engine LESS OBVIOUS CHANGES • Green plants convert sunlight into energy stored in chemical bonds • Eating corn (chemical potential energy) becomes other forms of energy in your body MECHANICAL ENERGY • Energy due to the position and motion of an object or objects in a system • mechanical energy = potential energy + kinetic energy MECHANICAL ENERGY • the total amount of potential and kinetic energy in a system • Sum of KE + PE • Bikes, Roller coasters, Swings, Rubber Bands all involve Kinetic & Potential Energy FALLING OBJECTS • Object has gravitational potential energy due to Earth pulling it down • Object becomes loose and accelerates downward due to gravity • Loses gravitational potential energy • Transformed into kinetic energy as speed increases PROJECTILE • Kinetic & Gravitational Potential Energy are converted between each other as ball rises and falls • Kinetic Energy gets ball moving • Kinetic Energy converted into GPE as ball rises • GPE greatest at peak of path • GPE converted back to Kinetic Energy as it moves downward and increases speed SWING • Push gets you moving • KINETIC ENERGY • Swing rises & loses speed • Kinetic changes into GRAVITATIONAL POTENTIAL ENERGY • Greatest at top of path • Swing accelerates downward • GPE changes into KINETIC ENERGY LAW OF CONSERVATION OF ENERGY • Energy cannot be created or destroyed • Energy simply changes from one form to another, but total amount of energy never changes WHY DON’T WE ALWAYS SEE CONSERVATION? • Friction & Air Resistance cause mechanical energy to be converted into thermal energy • That’s why chains get hot on a swing • Energy not created or destroyed, but changed into a new form NUCLEAR FUSION • Sun’s energy Light & Heat on Earth • Small amount of mass is transformed into tremendous amount of energy • Combining of 2 or more small nuclei into one larger nucleus In the reaction shown here, the nuclei of the hydrogen isotopes deuterium and tritium undergo fusion. NUCLEAR FISSION • Splitting of one large nucleus into 2 or more smaller nuclei • Power Plants create electrical energy using fission HUMAN BODY • Chemical Potential Energy maintains body temperature • Excess given off as heat to environment • CPE fuels processes such as heart beat and food digestion • Energy is converted into heat and movement HUMAN BODY • Obeys Law of Conservation of Energy • To maintain a healthy weight you must have a balance between energy consumed and energy used • Excess energy can be stored as fat FOOD ENERGY • Chemical Potential Energy • 1 food Calorie (C) = 4,184 Joules • 1 gram fat = 9 Calories • 1 gram of carbohydrates & proteins =4C IN-CLASS ASSIGNMENT/HOMEWORK • Continue working on Lecture Tutorial 1. 5.2 REINFORCEMENT ANSWERS – 29 PTS 2 pts Electrical Thermal 2. 2 pts Radiant/Light Thermal 3. 3 pts CPE Kinetic (thermal) AND Deputy = GPE sitting on Horse 4. 5 pts Waiter = CPE Kinetic AND Chandelier = GPE Electrical Light 5. 3 pts CPE Kinetic Sound Kinetic Electrical (CPE) 6. 5.2 REINFORCEMENT ANSWERS PTS 3 pts CPE thermal Kinetic &– PE 29 (mechanical) 7. 2 pts GPE Kinetic PE 8. 3 pts CPE Mechanical (KE & PE) Kinetic GPE 9. 3 pts CPE Kinetic thermal (friction) 10. 3 pts CPE thermal (friction) Mechanical (KE & PE)