1 / 40

Ch. 15 - Energy

Ch. 15 - Energy. I. Energy and Work (p.124-131) Energy and Work Energy Conservation of Energy. Energy and Work. What is energy? Whenever work is done, energy is transformed or transferred from one system to another When is work done?. Energy is the ability to do work. Energy and Work.

illana-leach
Download Presentation

Ch. 15 - Energy

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ch. 15 - Energy I. Energy and Work (p.124-131) Energy and Work Energy Conservation of Energy

  2. Energy and Work • What is energy? • Whenever work is done, energy is transformed or transferred from one system to another • When is work done? Energy is the ability to do work.

  3. Energy and Work • How are energy and work related? • REMEMBER: Work is done only when an object moves. • BUT energy can be present in an object or a system when nothing is happening. • HOWEVER it can only be observed when it is transferred from one object or system to another.

  4. SI Unit of Energy Because the amount of energy transferred is measured by how much work is done – energy and work are expressed in the same unit. Joules (J) is the unit of Energy

  5. Energy and Work • Work • transfer of energy through motion • force exerted through a distance W = Fd W: work (J) F: force (N) d: distance (m) 1 J = 1 N·m Distance must be in same direction of force!

  6. W d F Energy and Work • Brett’s backpack weighs 30 N. How much work is done on the backpack when he lifts it 1.5 m from the floor to his back? GIVEN: F = 30 N d = 1.5 m W = ? WORK: W = F·d W = (30 N)(1.5 m) W = 45 J

  7. W d F Energy and Work • A dancer lifts a 40 kg ballerina 1.4 m in the air and walks forward 2.2 m. How much work is done on the ballerina during and after the lift? GIVEN: m = 40 kg d = 1.4 m - during d = 2.2 m - after W = ? WORK: W = F·d F = m·a F =(40kg)(9.8m/s2)=392 N W = (392 N)(1.4 m) W = 549 J during lift No work after lift. “d” is not in the direction of the force.

  8. Potential Energy AKA – Energy of Position Potential Energy is energy that is stored. You can’t see it but you know it’s there.

  9. Types of Potential Energy

  10. Gravitational Potential Energy AKA - GPE • Depends on mass and height. • GPE = m g h Or • GPE = mass x free-fall acceleration x height (mg = weight in Newtons) Mass (m) = kg; Gravity (g) = 9.8 m/s2; Height (h) = m

  11. Gravitational Potential Energy Potential Energy (PE) • stored energy • cannot be seen • depends on position or configuration of an object • Which boulder has greater gravitational PE? • What other ways can an object store energy?

  12. Example • A 65 kg rock climber ascends a cliff. What is the climber’s gravitational potential energy at a point 35 m above the base of the cliff? • Given: m = 65kg h = 35 m g = 9.8m/s GPE = ? GPE = mgh GPE = 65 x 9.8 x 35 2 GPE = 22,295 J

  13. Kinetic Energy • is the energy of motion.

  14. Which has the most KE? • Which has the least KE? 80 km/h 50 km/h 80 km/h Kinetic Energy • Kinetic Energy (KE) • energy in the form of motion • depends on mass and velocity 80 km/h truck 50 km/h motorcycle

  15. Kinetic Energy AKA = KE KE = ½ mass x velocity OR KE = ½ m v mass (m) = kg velocity (v) = m/s 2 2

  16. Note: Kinetic energy depends more on speed than on mass.

  17. Example • What is the kinetic energy of a 44kg cheetah running at 31 m/s? Given: m = 44 kg v = 31 m/s KE = ? KE = ½ m v 2 2 KE = ½ (44) x (31) KE = 22 x 961 KE = 21142 J

  18. Forms of Energy • Forms of Energy: • Each of these forms of energy can be converted into other forms of energy.

  19. THERMAL The ability to cause change. MECHANICAL NUCLEAR ELECTRICAL CHEMICAL joules (J) Energy internal motion of particles ENERGY motion of objects changes in the nucleus motion of electric charges bonding of atoms

  20. Energy Electrical energy: • results from the flow of charged particles or electrons. Electric charges can exert forces that do work. Chemical Energy • is the energy stored in chemical bonds – when the bonds are broken, the released energy can do work.

  21. Energy Mechanical Energy • the energy associated with the motion or position of an object. The sum of potential and kinetic energy in a system (Usually involves movement of an object) • Nuclear Energy: energy stored in atomic nuclei – nuclear fission releases energy by splitting nuclei apart, nuclear fusion releases energy by combining 2 nuclei into a larger nuclei.

  22. Energy Electromagnetic Energy: a form of energy that travels through space in the form of waves (visible light and X-rays are examples). Thermal Energy: • energy given off as heat (friction). The total potential and kinetic energy of all the microscopic particles in an object.

  23. Energy Conversions The process of changing energy from one form to another.

  24. Law of Conservation of Energy • Energy can not be created nor destroyed, it can only be changed. • Energy can be transferred to another object/system or to another form.

  25. Conservation of Energy • Law of Conservation of Energy • Energy may change forms, but it cannot be created or destroyed under ordinary conditions. • Example: • PE  KE • mechanical  thermal • chemical  thermal

  26. E. Conservation of Energy PE  KE View pendulum animation. View roller coaster animation.

  27. E. Conservation of Energy Mechanical  Thermal View rolling ball animations. View skier animation.

  28. Ch. 5 - Energy II. Thermal Energy Temperature Thermal Energy Heat Transfer

  29. A. Temperature • Temperature • measure of the average KE of the particles in a sample of matter.

  30. B. Thermal Energy • Thermal Energy • the total energy of the particles in a material. • KE - movement of particles • PE - forces within or between particles due to position. • depends on temperature, mass, and type of substance.

  31. 80ºC 80ºC 400 mL A B 200 mL B. Thermal Energy • Which beaker of water has more thermal energy? • B - same temperature, more mass

  32. C. Heat Transfer • Heat • thermal energy that flows from a warmer material to a cooler material. • Like work, heat is... • measured in joules (J) • a transfer of energy

  33. C. Heat Transfer • What are 3 types of heat transfer? • Conduction • Convection • Radiation

  34. D. Conduction • Transfer of heat as a result of direct contact

  35. E. Convection

  36. F. Radiation

  37. Summary

  38. Quiz

  39. 80ºC 10ºC A B C. Heat Transfer • Why does A feel hot and B feel cold? • Heat flows from A to your hand = hot. • Heat flows from your hand to B = cold.

  40. C. Heat Transfer • Specific Heat (Cp) • amount of energy required to raise the temp. of 1 kg of material by 1 degree Kelvin • units: J/(kg·K)or J/(kg·°C)

More Related