Kinetic & Potential Energy Notes Energy Transfer Diagrams Notes Energy: –The ability to produce change –Kinetic: motion –Potential: stored 1

2 Work & Power Work 1.The product of the Force exerted on an object and the distance that object travels due to that force symbol: W units: N*m= Joule Power 1. Work done over time 2. The rate at which work is done symbol: – P Units: – J/sec = Watt (W) 1 HP (horsepower) = 746 W P

Kinetic Energy If an object is moving, at any speed, it exhibits energy –Def.: The energy of an object due to its motion symbol: KE units: Joules Since a force is required to change the state of an object’s motion (Izzy’s 2nd), it makes sense that to change the energy of an object, external Work must be done. Work-Energy Theorem We will use one kind of Kinetic energy, “Translational,” since any object is moving. Moving molecules we call heat, and vibrating molecules we call sound.

Potential Energy If an object ain’t moving, it may not exhibit energy… but it could! –Def.: The energy of an object due to its position or condition symbol: –PE units: –J–J There are a number of different types of Potential Energy (since there are so many positions & conditions for an object) We will focus on the position of an object with respect to the ground- Gravitational Potential Energy

Conservation of Energy The Total Energy in a system cannot change –…Unless Work is done on the system from outside Consider Mr. McGuire on his Alma Mater, Cass Tech!(mine is only 1 floor so doesn’t work) That Total Energy might be split between Potential & Kinetic, and energy can go back & forth between the two KE = 0 J PE = 100,000 J m = 100 kg y = 100 m PE = J y = 66 m v = 0 m/sec KE = J

6 Conservation of Energy The Total Mechanical Energy in a system cannot change – That Total Energy might be split between Potential & Kinetic, and energy can

Energy Transfer Diagrams Also known as Energy Flow Diagrams They show: – Sequence of forms of Energy – Arrows showing direction of sequence – Cause of transfer from one form of Energy to the next What is doing Work on the object (written above the arrow) PotentialKinetic Earth/Gravity

Energy Transfer Diagrams Also known as Energy Flow Diagrams They show: – Sequence of forms of Energy – Arrows showing direction of sequence – Cause of transfer from one form of Energy to the next What is doing Work on the object (written above the arrow) PotentialKinetic Earth/Gravity

Elevator lifting Gladys to the top of a building Energy Transfer Diagrams PotentialKinetic Motor Electric Cable

Energy Transfer Diagrams A taco in a cart is rolled up a hill, and it coasts to a stop + Potential Kinetic Earth Kinetic Earth + Heat Potential + Heat Friction

Energy Bar Charts As we have seen, Total Mechanical Energy (TME) for a system can actually increase or decrease… – …only if (external) Work is done on it Initial Energy + Work = Final Energy TME i + W = TME f KE i + PE i + W = KE f + PE f

Energy Bar Charts Example 1: A plate of lasagna falls to the ground – Starts out with only PE – Ends with KE Example 2: Hernandez, obeying the 5-sec rule, picks up the lasagna – Starts out with Zero KE & PE – Hand does Work on Lasagna – Ends with PE

Energy Bar Charts Example 1: A plate of lasagna falls to the ground – Starts out with only PE – Ends with KE Example 2: McGuire, obeying the 5-sec rule, picks up the lasagna – Starts out with Zero KE & PE – Hand does Work on Lasagna – Ends with PE