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 = potential energy + kinetic 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 Swing rises & loses speed 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

Chemical Potential Energy 1 food Calorie (C) = 4,184 Joules Food Energy Chemical Potential Energy 1 food Calorie (C) = 4,184 Joules 1 gram fat = 9 Calories 1 gram of carbohydrates & proteins = 4 C

In-Class Assignment/Homework Continue working on Lecture Tutorial

5.2 reinforcement Answers – 29 pts 2 pts Electrical  Thermal 2 pts Radiant/Light  Thermal 3 pts CPE  Kinetic (thermal) AND Deputy = GPE sitting on Horse 5 pts Waiter = CPE  Kinetic AND Chandelier = GPE Electrical  Light 3 pts CPE  Kinetic  Sound  Kinetic  Electrical (CPE)

5.2 reinforcement Answers – 29 pts 3 pts CPE  thermal  Kinetic & PE (mechanical) 2 pts GPE  Kinetic  PE 3 pts CPE  Mechanical (KE & PE)  Kinetic  GPE 3 pts CPE  Kinetic  thermal (friction) 3 pts CPE  thermal (friction)  Mechanical (KE & PE)