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Conservation of energy

Conservation of energy. Conservation of energy. For an isolated, closed system Energy is not created or destroyed, only transferred or transformed. Conservation of Energy. Like momentum, energy can be transferred from one object to another

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Conservation of energy

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  1. Conservation of energy

  2. Conservation of energy For an isolated, closed system Energy is not created or destroyed, only transferred or transformed

  3. Conservation of Energy Like momentum, energy can be transferred from one object to another Unlike momentum, energy can also be transformed from one type to another

  4. Conservation of energy Closed system – energy remains constant in system over time Open system – energy flows in/out of the system

  5. Change in Energy Energy Transformations: Energy is utilized in everyday life through by being transferred or transformed. Transferred means energy is passed from one object to the next Transformed means energy is changed from one type to at least one other type

  6. TRANSFERRING AND TRANSFORMING ENERGY

  7. Transfer of Kinetic energy Switching a light switch on or off Bumping into someone Kicking a ball Can you think of 3 more transfers of Kinetic energy between 2 objects since you woke up?

  8. Transfer of kinetic to potential Load an object up with more energy than what it had at the start. Lifting a book off the desk Stretching a rubberband Can you think of 3 more examples of loading an object with more potential energy you witnessed this morning?

  9. Transfer is not always a one to one experience Energy may be transferred to more than one object or energy type at any instant in time

  10. Cliff diver What type of mechanical energy does he have before he dives off the cliff? At the midway point of the dive As he enters the water

  11. Example problem A 50 kg man dives off a 20 m high cliff. Assuming his initial velocity was zero and no air resistance: Determine the initial amount of GPE the man has Determine how much KE he has halfway through the dive Determine the velocity at which he is falling halfway through the dive.

  12. Energy transformations/transfers explain the bouncing of a ball

  13. Basketball drop Observe the action of the basketball being dropped. List the types of energy changes that occur between the basketball, the ground and the surrounding air through the entire event Does the ball have the same amount of energy at the end as it had at the moment of release?

  14. Ball As ball drops, GPE is transformed into KE A tiny amount is lost to air resistance, sound

  15. OTHER EXAMPLES OF CONSERVATION OF ENERGY

  16. SYSTEMS

  17. DETERMINATION OF ENERGY DURING CONSERVATION

  18. Conservation of energy Energy can not be created or destroyed, only transformed or transferred in a closed system Before EventAfter Event KEi + GPEi + EPEi = KEf + GPEf + EPEf

  19. The equation can be expanded to handle more types of energy

  20. Question A high jumper jumps 2.04 m. If the jumper has a mass of 67 kg, what is his gravitational potential energy at the highest point of the jump?

  21. What is given? 2.04 m Height at highest point of jump 67 kg Mass of person

  22. What is wanted? What is his gravitational potential energy at the highest point of the jump? GPE

  23. What equation to use Need to connect GPE with mass and height GPE = mgh G is the acceleration due to gravity G is constant on earth’s surface = 9.8 or 10

  24. Plug in and solve GPE = m g h GPE = (67) (10) (2.04) Around 1300 J The units are the units for energy, which can be used if all else is measured in m, kg, and s

  25. Example A 65 kg person begins to roll down a roller coaster hill. At some point they are moving a 12 m/s and are still 100 m off the ground. A) what is the total mechanical energy of the person? B) do they have more KE or GPE?

  26. Follow up question As they continue down the hill, they reach a point where the car is only 17 m off the ground. If the system is closed, how fast is the person going?

  27. NON-CONSERVATIVE FORCES

  28. Is energy conserved in any event? If not, how could we measure the loss of energy?

  29. Non-conservative situations Any situation where there is a change in the overall amount of energy in a system

  30. Loss of energy of a roller coaster Some of the total energy of the roller coaster is lost: while overcoming friction between track and car while overcoming friction between air and car producing sounds of the coaster Roller Coaster is not a closed system by it self

  31. Non- conservative forces Any force that adds energy into a closed system OR takes energy out of a closed system Friction Air Resistance Applied forces

  32. Non-conservative forces Friction Air-resistance Applied force Internal forces on an object

  33. Results on the application of a non-conservative force Energy is either added or taken out of the system because work is done

  34. To determine the amount of energy lost or work done by non-conservative forces Work lost due to non conservative forces equals the difference in energy before and after application of force Wl = Ef – Ei Positive result indicates energy was put into system

  35. Remember W = f x d Can solve for displacement or size of force

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