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Chapter 4

Chapter 4. Energy. What is energy?. Def: ability to cause change Every change involves energy. Different Forms. Electrical Chemical – stored in food, involved in reactions Radiant – gives off Thermal – heat Same thing just different forms. Kinetic Energy.

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Chapter 4

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  1. Chapter 4 Energy

  2. What is energy? • Def: ability to cause change • Every change involves energy

  3. Different Forms • Electrical • Chemical – stored in food, involved in reactions • Radiant – gives off • Thermal – heat • Same thing just different forms

  4. Kinetic Energy • Def: energy of a moving object • Depends on mass and speed • Kinetic energy (Joules) = 1mass (kg) x [speed (m/s)]2 2 • KE = 1 mv2 2 • SI unit for energy is joule (J)

  5. Practice! • What is the kinetic energy of a .15 kg baseball moving at 40 m/s. • A car moving at a speed of 20 m/s has a kinetic energy of 300,000 J. What is the car’s mass?

  6. Potential Energy • Even motionless objects have energy • Stored in the object, has potential to change • Def: stored energy

  7. Elastic Potential Energy • Def: stored energy by something that can stretch or compress • Stretched rubber band – elastic potential energy  kinetic energy

  8. Chemical Potential Energy • Def: energy stored in chemical bonds • Food, gasoline, etc.

  9. Gravitational Potential Energy • Def: stored energy by objects due to position above earth (able to fall)

  10. Practice! • Find the height of a .15 kg baseball that has a GPE of 73.5 J. • Find the GPE of a .3 kg coffee mug on a 1-m high counter. • What could you do to change GPE? • Change height or mass

  11. Section 2 Conservation of Energy

  12. Changing Forms of Energy • Changing electrical energy – electricity – light and heat energy • Energy is constantly changing forms

  13. Transforming Chemical Energy • Cars – MANY energy transformations • Spark plug – gasoline – engine - wheels

  14. Transforming Chemical Energy • Green plants – take in sunlight and transform to chemical energy in plants

  15. Mechanical Energy • Def: total amount of potential and kinetic energy Mechanical Energy = Potential + Kinetic

  16. Falling Objects • As potential  kinetic mechanical energy stays same • Potential lost = kinetic gained

  17. Projectile Motion • Mechanical energy remains constant • Still see transformations of energy

  18. Swinging • Best part is falling from highest point • High GPE = Low KE • Describe transition…

  19. Law of Conservation of Energy • Def: energy can not be created or destroyed • Energy just changes form • All energy in the universe does not change • Energy in = Energy out

  20. Is energy always conserved? • Swinging – you eventually will stop – where does all the energy go? • Friction – air resistance = thermal energy

  21. Human Body – Energy Relations • What forms of energy are in your body? • Conservation of energy still true • Food, fat = potential energy • Activity = kinetic energy • Calorie 1C = 4,184 J

  22. Chapter 6 Section 1 Temperature and Heat

  23. Matter in Motion • Matter is made of tiny particles in constant motion  have kinetic energy • Faster = more kinetic energy

  24. Temperature • Def: measure of average kinetic energy of particles • High Temp. = High Energy • Low Temp. = Low Energy • Unit  Kelvin

  25. Thermal Energy • Collisions between air and butter particles increase energy of butter = higher temperature • Def: sum of kinetic and potential energy of particles in object

  26. Thermal Energy • As temp increases = thermal energy increases • If object has MORE MASS and at the same temp. has HIGHER thermal energy

  27. Heat • Is your seat toasty? • Def: thermal energy that flows from something at a higher temp to a lower temp • Unit: Joule

  28. Beachin’ it up! • How can there be extreme differences in temperature from air, sand and water? • Sun rays are the same why different temp? • Sand heats up 6 times faster than water

  29. Specific Heat • Specific Heat: heat needed to raise 1kg of material by 1C

  30. Water as a Coolant • It’s high specific heat – absorb a lot of heat without changing temp much • Strong bonds have to be broken before particles move really fast

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