8 TH GRADE ENERGY UNIT

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

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4. Categories of Energy

5. 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

6. 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 causing gravity to affect it more. • GPE: height of object (h) x mass (m) = ______ Joules (J)

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8. Work

9. 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.

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

11. 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)

12. Transfer & Transformation • TRANSFER • Air particles • Surface & cup GPE KE KE GPE TRANSFORMATION

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

14. 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)

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

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

17. Energy Chains • Energy can transfer & transform. • This reaction forms “energy chains”, where we can map out energy’s change. We usually start with the Sun

18. 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 objects, usually a sliding motion.

19. 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!!!

20. Activity #7 Force (pulling) • KE can be transferred and some of it transforms into heat energy. Friction transfers energy… • more force = more friction = more KE transfer = more heat energy!! Force of Friction

22. Thermal & Heat Energy If all matter has KE, then it must possess Thermal Energy!!

23. Phases of Matter

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

25. Temperature • Temperature measures the “average KE” (motion) of particles that make up a substance. • Thermometers are the instruments we use. • Liquid thermometers (water, alcohol, & liquid mercury) work by thermal expansion & contraction.

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

27. What is Thermal Energy? • The TOTAL energy of all the particles in a substance (matter). • 3 Factors to find thermal energy: • Must know the avg. KE (temp.) • Must know how much (mass or volume) • Must know the arrangement of particles (solid, liquid, or gas) which one has A more thermal B energy? 100 ml of water 125 ml of water at 30 C at 30 C

28. 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

29. 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!!

30. 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!

31. 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).

32. Phase change names

33. Phase change graph

34. 3 ways “heat energy” moves… • CONDUCTION • CONVECTION • RADIATION

35. 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

36. Conductor vs. Insulator • A good conductor is a substance that allows heat to transfer through it easily. • A bad conductor (Insulator) is a substance that does NOT allow heat to transfer very well toward the cooler area.

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

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

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

40. 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.

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

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

43. 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.

44. FLAME Wax 1 Wax 2 Wax 3 ROD

45. 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.)

46. 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.

47. Final set-up for Investigation #11

49. CONVECTION • Represents the 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

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