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8 TH GRADE ENERGY UNIT

8 TH GRADE ENERGY UNIT. What is ENERGY ?. ENERGY – The ability to do work or create a change. Law of Conservation : Energy is neither created nor destroyed…only changes form & position. WORK – Force exerted on an object (matter) that causes it to move…energy is needed!

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8 TH GRADE ENERGY UNIT

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  1. 8TH GRADE ENERGY UNIT

  2. What is ENERGY? • ENERGY – The ability to do work or create a change. • Law of Conservation: Energy is neither created nor destroyed…only changes form & position. • WORK – Force exerted on an object (matter) that causes it to move…energy is needed! • W : force x distance moved = ____joules

  3. Kinetic Energy • Kinetic Energy (KE) – The energy of an object due to its motion. • How to find kinetic energy: KE: Mass of object x Velocity ² ÷ 2 =____Joules

  4. Potential Energy / GPE • Potential Energy – Energy that is stored and held in readiness. • Gravitational PotentialEnergy (GPE) – Potential energy that depends on the height of object from surface. • GPE: height of object (h) x mass (m) =

  5. LAB Reviews • Transferof energy means to pass energy from one place to another (one object to another) without changing forms. • Transformationof energy means that energy has changed from one form to another.

  6. Ball & Ramp Less GPE = less speed = less KE GPE KE GPE KE More GPE = higher speed = more KE GPE KE GPE KE

  7. Passing energy along… The KE from the ball was transferred (passed) to the Styrofoam cup…the ball lost KE and the cup gained KE…Work was done!! (Cup absorbed the KE from ball)

  8. Transfer & Transformation • TRANSFER • Air particles • Surface (ramp & floor) • Cup GPE KE KE GPE TRANSFORMATION

  9. Pendulum demonstration GPE KE GPE KE GPE KE GPE KE GPE KE GPE KE GPE KE • Transformation of Energy GPE KE GPE again…

  10. Roller Coaster ‘W’ has the greatest GPE, so ‘X’ will have the greatest KE. The rest of the roller coaster ride will run fine because it has enough initial KE to make it over the rest of the smaller hills.

  11. Energy transfer (absorbed) – activity #5 • How does type of surface affect energy transfer? • Surfaces whose particles are tightly packed can only absorb a little bit of energy at a time (many bounces) • Surfaces whose particles are loosely packed can absorb more energy at a time (less bounces)

  12. Bouncing Ball GPE KE GPE KE Floor accepts less energy at a time… more dense Cardboardaccepts more energy at a time…less dense

  13. Activity #7 (transfer of energy) KE is transferred from person rope wood.

  14. Activity #7 (transformation of energy Because of FRICTION between the rope and wood, the KE transformed into heat !! HOT

  15. Phase Change Particle Model Low KE medium KE High KE

  16. Phase change names melting vaporization condensation freezing

  17. Phases of Matter • Melting – Phase change from solid to liquid. Increased KE of particles from added energy • Vaporization – Phase change from liquid to gas. Lots of KE from added energy. • Condensation – Phase change from gas to liquid. Less KE of particles from loss (transfer) of energy. • Freezing – Phase change from liquid to solid. Very low KE of particles.

  18. Activity #8 (phase change) In this activity, energy was added to the ice which caused increased KE and then phase changes. The reason the graph has areas where temperatures don’t rise is because the energy at that point is not used to heat the substance, but rather change the phase…then heating continues.

  19. What is Thermal Energy? • The TOTAL energy of all the particles that make up a substance (matter). • 3 Factors to find thermal energy: • Temp. • Amount (mass or volume) • Phase (solid, liquid, or gas)

  20. Temperature • Thermometers measure temperature… • Temperature measures the “average KE” (motion) of particles that make up a substance.

  21. What is heat ? • Heat is the actual transfer of Thermal Energy. When Thermal Energy is transferred from one place to another, we call it “heat.” Thermal energy gets transferred to the air, then to the person (HEAT). Fire has LOTS of Thermal Energy

  22. Transformation of Energy examples… • Engine = chemicalkinetic • Heater = chemicalheat • Solar = radiantelectrical • Battery = chemical electrical • Food = chemicalheat / KE • Photosynthesis = radiant chemical

  23. Energy Chains • Energy can transfer & transform. • This reaction forms “energy chains”, where we can map out the transfer & transformation of energy. We usually start with the Sun

  24. Phases of Matter

  25. What becomes of KE? What becomes of KE after it transfers? • When KE transfers from one place to another through physical contact, it not only gives the energy of motion, but also transforms into heat energy! • Friction – A resistance between 2 or more particles or objects causes KE to transfer.

  26. Different Temperature Scales Absolute Zero K: Point at which all motion has stopped…no energy!!

  27. Force • In order for KE to be transferred or transformed, there must be something making “matter” accelerate or change direction. • Force = is a push or pull that causes a substance with mass (takes up space) to accelerate in a certain direction. • Force can change amount of friction!!!

  28. Thermal Expansion & Contraction • In physics, thermal expansion is the tendency of matter to change in length or volume in response to a change in temperature. When a substance is heated, its particles move around more vigorously and by doing so generally maintain a greater average separation. This requires more space!!

  29. 1st Law of Thermodynamics • States that energy is neither created nor destroyed…it is just passed along and/or transformed (conservation of energy). • All the energy that is in the universe right now can only change position or form!

  30. 2nd Law of Thermodynamics • Thermal energy flows (heat) spontaneously from a warmer body to a cooler one. • One cannot transfer or transform heat completely into useful work, some of the energy becomes unusable… • Every isolated system becomes disordered in time (entropy).

  31. 3 ways Thermal Energy transfers (heat) • CONDUCTION • CONVECTION • RADIATION

  32. CONDUCTION • Process where heat energy is transferred by physical contact through a substance. Particles of a substance have to touch each other to pass heat from warmer to cooler. Cooler area, gaining KE… warming up Warmer area, Lots of KE Collision of particles

  33. Conductor vs. Insulator • Conductor – A substance that allows heat to transfer through it. • Insulator – A substance that does NOT allow heat to transfer to the cooler area easily.

  34. Insulators Fire gear: keeps heat from skin exposure Space suit keeps heat from sun minimal Ice actually slows the transfer of heat from inside to outside

  35. CONVECTION • Transfer of heat by circulation or movement of the hot particles to cooler areas. Warmer, less dense fluids rise, while cooler, more dense fluids fall and replace. Warm, less dense air rises…cools Cool, more dense air falls…warms again

  36. RADIATION • Energy that travels through the emptiness of space…does not need particles to transfer (medium). Travels by electromagnetic wavesaway from a heat source.

  37. Investigation #11Conduction • Purpose / Question: • To observe how HEAT energy moves by conduction. • Do some substancesallow heat energy to conduct better than others?

  38. Background Knowledge: • Look at the demonstration. Which spoon would you pick up first? metal or plastic • Why?

  39. Hypothesis: • Rods with more mass will (allow / not allow) heat to transfer well. • Rods with less mass will (allow / not allow) heat to transfer well.

  40. Experiment Materials: • Solid rods (aluminum, steel, brass, glass) • Hollow rods (brass & aluminum) • 2 clothes pins • Candles • Large paper • 2 blocks • Timer • Safety goggles!!!

  41. Procedure • Find the mass of each type of rod (g) and record in data table. • Be very precise in measurements! Metal Rod

  42. 3. Take one rod (save glass rod for last) and line it up on template. • 4. Using the marker, place a line where the 3 globs of wax will be resting & flame line. • Flame line = 3inches from edge. • Wax 1 = 2 inches from edge. • Wax 2 = 1 inch from edge. • Wax 3 = very edge of rod.

  43. FLAME Wax 1 Wax 2 Wax 3 ROD

  44. 5. Light big candle and allow wax to run off and drip onto the designated 3 areas for wax globs (edge, 1in., and 2 in.)

  45. 6. Use the clothes pins to suspend the bar above the surface. • 7. stack 2 blocks & place a lit candle directly under the inner-most marked line on bar. • 8. Once flame hits the bar, start timing. • 9. You are looking for how long it takes each glob of wax to start melting. • 10. Write observation times in data table.

  46. Final set-up for Investigation #11

  47. CONDUCTION Process where heat energy is transferred by physical contact through a substance. Particles of a substance have to touch each other to pass heat from warmer to cooler. Cooler area, gaining KE… warming up Warmer area, Lots of KE Collision of particles

  48. What is Radiation? • All energy, typically from a light source like a star (Sun) that transfers energy without a medium (but can transfer some through liquids & gases) • A medium refers to anything made up of particles (solids, liquids, gases)

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