Kinetic Potential Energy Notes Energy Transfer Diagrams Notes

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

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

Kinetic Energy • 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 2 nd), 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 • There a number of If an object ain’t moving, it different types of Potential may not exhibit energy… but Energy (since there are so it could! many positions & – Def. : The energy of an object conditions for an object) due to its position or • We will focus on the condition position of an object with • symbol: respect to the ground– PE Gravitational Potential • units: Energy – J

Conservation of Energy m = 100 kg • The Total Energy in a system y = 100 m cannot change – …Unless Work is done on the system from outside • Consider Mr. Mc. Guire 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 v = 0 m/sec KE = 0 J PE = 100, 000 J y = 66 m PE = 66000 J KE = 34000 J

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) Earth/Gravity Potential Kinetic

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

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

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 TMEi + W = TMEf KEi + PEi + W = KEf + PEf

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