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Ch.9, Sec.3 – Conservation of EnergyCh.9, Sec.3 – Conservation of Energy
Where Does the Energy Go?Where Does the Energy Go?
frictionfriction: a force that opposes motion between two surfaces : a force that opposes motion between two surfaces that are in contact that are in contact
- on a roller coaster, not all potential energy is converted into on a roller coaster, not all potential energy is converted into kinetic energy because of friction!kinetic energy because of friction!
- kinetic energy can be converted into thermal energy instead kinetic energy can be converted into thermal energy instead of going back to potentialof going back to potential
Energy Is Conserved Within a Closed SystemEnergy Is Conserved Within a Closed System
- a closed system is a group of objects that transfer energy a closed system is a group of objects that transfer energy only to each otheronly to each other
- energy is always conserved and never lost!energy is always conserved and never lost!
Ch.9, Sec.3 – Conservation of EnergyCh.9, Sec.3 – Conservation of Energy
law of conservation of energylaw of conservation of energy: this law states that energy : this law states that energy cannot be created or destroyed but can change from one cannot be created or destroyed but can change from one form to anotherform to another
- the total amount of energy in a closed system is always the total amount of energy in a closed system is always the samethe same
- energy is conserved in all cases & no exception has energy is conserved in all cases & no exception has been found!been found!
No Conversion Without Thermal EnergyNo Conversion Without Thermal Energy
- thermal energy due to friction is NOT useful (it cannot be thermal energy due to friction is NOT useful (it cannot be used for work)used for work)
- example: car (wasted thermal energy leaves the radiator & example: car (wasted thermal energy leaves the radiator & the exhaust)the exhaust)
Ch.9, Sec.3 – Conservation of EnergyCh.9, Sec.3 – Conservation of Energy
- perpetual motion is NOT possible because a constant perpetual motion is NOT possible because a constant energy supply is neededenergy supply is needed
- energy efficiency is a comparison of the amount of energy energy efficiency is a comparison of the amount of energy before a comparison with the amount of useful energy after before a comparison with the amount of useful energy after a conversiona conversion
