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Warm up 11/15

Warm up 11/15. Create a KWL as page #9 in your notebook like below and complete columns K and W. 9-3 Conservation of Energy. Where’d the energy go?. When two surfaces are touching, the force of friction opposes the motion between the two object

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Warm up 11/15

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  1. Warm up 11/15 Create a KWL as page #9 in your notebook like below and complete columns K and W

  2. 9-3 Conservation of Energy

  3. Where’d the energy go? • When two surfaces are touching, the force of friction opposes the motion between the two object • Place your hand on the table in front of you and slide your hand across the table • Do you feel any drag keeping your hand from easily moving? • Try it again against the bottom of your shoe • Why do you feel more resistance on your shoe than the desk?

  4. How do you get past friction? • Energy must be used to overcome friction • Think of a roller coaster • The wheels of a roller coaster run along the tracks creating friction between them • There is also friction between the cars of the roller coaster and the air around them • The roller coaster can never reach the same height of the highest hill without help from a chain pulling it up • This is because not all of the potential energy at the top of the hill is converted into kinetic energy • Some of this energy is converted into friction!

  5. This system is closed • A closed system is a group of objects that transfer energy only to each other • Ex: a roller coaster, the track and the air around it • When a roller coaster runs along its track, some of the mechanical energy (potential and kinetic energy) is used to overcome friction • When this happens, it is turned into thermal energy which can be felt as heat • Think about when you rub your hands together – after a period of time, your hands feel hot • The potential energy at the top of the first hill is equal to the kinetic energy + thermal energy from friction + sound energy produced

  6. Its all about conservation • Just like you conserve mass in chemistry, we all also conserve energy in physics • The law of conservation of energy tells that energy is not created or destroyed • the total amount of energy in a closed system is always the same • Energy can be converted into other forms, but you will always have the same amount • Any time energy is converted from one form to another, there is always conversion into thermal energy • This is not useful energy • It can not be used to do any additional work

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