1. Ch.9, Sec.3 – Conservation of Energy Where Does the Energy Go? Where Does the Energy Go?  friction: a force that opposes motion between two surfaces that are in contact - on a roller coaster, not all potential energy is converted into kinetic energy because of friction! - kinetic energy can be converted into thermal energy instead of going back to potential Energy Is Conserved Within a Closed System Energy Is Conserved Within a Closed System - a closed system is a group of objects that transfer energy only to each other - energy is always conserved and never lost!

2. Ch.9, Sec.3 – Conservation of Energy  law of conservation of energy: this law states that energy cannot be created or destroyed but can change from one form to another - the total amount of energy in a closed system is always the same - energy is conserved in all cases & no exception has been found! No Conversion Without Thermal Energy No Conversion Without Thermal Energy - thermal energy due to friction is NOT useful (it cannot be used for work) - example: car (wasted thermal energy leaves the radiator & the exhaust)

3. Ch.9, Sec.3 – Conservation of Energy - perpetual motion is NOT possible because a constant energy supply is needed - energy efficiency is a comparison of the amount of energy before a comparison with the amount of useful energy after a conversion