1 / 72

Do now!

Do now!. 1 Energy Types Word Scramble 2 Title – Energy Flow diagrams and the date. Kinetic energy (KE) Energy due to a body’s motion. Potential energy (PE) Energy due to a body’s position Thermal energy Energy due to a body’s temperature. Chemical energy

thomaskelly
Télécharger la présentation

Do now!

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. Do now! 1 Energy Types Word Scramble 2 Title – Energy Flow diagrams and the date

  2. Kinetic energy (KE) Energy due to a body’s motion. Potential energy (PE) Energy due to a body’s position Thermal energy Energy due to a body’s temperature. Chemical energy Energy associated with chemical reactions. Nuclear energy Energy associated with nuclear reactions. Electrical energy Energy associated with electric charges. Elastic energy Energy stored in an object when it is stretched or compressed. Some examples of forms of energy All of the above forms of energy (and others) can ultimately be considered to be variations of kinetic or potential energy.

  3. Learning Today • Energy flow diagrams • Energy flow circus • Sankey diagrams • Potential Energy – P.E. • Homework Potential Energy Sheet

  4. Other energy measurement examples

  5. Conservation of energy Energy cannot be created or destroyed. It can only be transformed from one form to another form. Conservation of energy also means that the total energy in the universe stays constant.

  6. Energy Flow diagrams – Copy please Energy flow diagrams show energy transformations. Work done = energy transformed For example, when a car brakes, its kinetic energy is transformed into heat energy in the brakes. Kinetic heat

  7. Energy changes 1) Write down the starting energy: 3) Write down what energy types are given out: Electricity Light + heat 2) Draw an arrow To describe an energy change for a light bulb we need to do 3 steps: • Draw energy flow diagrams for the following…? • An electric fire • A rock about to drop • An arrow about to be fired

  8. Television What are the main energy transfers for a television (don’t forget the wasted energy)? light sound electrical heat

  9. Car engine What are the main energy transfers for a car engine (don’t forget the wasted energy)? kinetic sound chemical heat

  10. Radio What are the main energy transfers for a radio (don’t forget the wasted energy)? sound heat electrical

  11. Pendulum oscillation MINIMUM MAXIMUM MAXIMUM ZERO GRAVITATIOINAL POTENTIAL ENERGY KINETIC ENERGY The total energy, gravitational potential plus kinetic, remains the same if there are no significant resistive forces

  12. Wasted sound energy Can you name some devices that waste energy as sound? _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ Hairdryer Washing machine Car engine Computer Microwave Bunsen burner Wind turbine Dish washer

  13. Radio Television Car engine Wasted heat energy Can you name some devices that waste energy as heat? _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ Computer Turbine Motor Transformer Any electrical device

  14. What happens to wasted energy? What happens to the wasted energy you get whenever energy is changed from one form to another? reated estroyed Remember energy can not be c______ or d_______. Wasted e_____ spreads out (d_______) into the s_________. nergy issipated urroundings This makes the energy harder to r____. e-use This is why it is important to r_____ the amount of wasted energy there is. educe

  15. Energy Transfer diagrams Consider a light bulb. Let’s say that the bulb runs on 100 watts (100 joules per second) and transfers 20 joules per second into light and the rest into heat. Draw this as a diagram: “Input” energy “Output” energy 20 J/s light energy 100 J/s electrical energy 80 J/s heat energy (given to the surroundings)

  16. Example questions Consider a kettle: Consider a computer: 2000 J/s electrical energy 150 J/s electrical energy 20 J/s wasted heat Wasted heat Heat to water Useful light and sound 10 J/s wasted sound Sound energy • Work out each energy value. • How much energy is converted into useful energy?

  17. Here is a more complex energy transformation diagram, the sort used by engineers.  This one is for an aeroplane engine.

  18. Choose appropriate words to fill in the gaps below: Energy is required to do ________. Energy is measured in ________ (J) Energy cannot be created or ___________ but can only change ________. Kinetic energy is the energy possessed by __________ bodies. When an object is lifted up it gains gravitational _____________ energy. Heat or __________ energy is often produced as a _________ energy form, dissipated to the surroundings. work joules destroyed form moving potential thermal wasted WORD SELECTION: destroyed potential moving joules thermal work wasted form

  19. Do Now How much energy sort, please arrange the statements in order of how much energy is involved .

  20. Energy to drive a car 60 miles: 250,000,000 J • Energy stored in 1 litre of petrol: 34,000,000 J • Energy used by the human body for 1 day: 10,000,000 J • Energy in 1 unit on electricity bill (costs 15p): 3,600,000 J • Energy in a typical chocolate bar: 1,000,000 J • Energy to boil 1 l of water, from freezing: 500,000 J • Energy stored in a peanut: 25,000 J • Kinetic energy of a fast-moving cricket ball: 1000 J • Energy stored in one new AA battery: 1000 J • Energy from burning one whole match: 1000 J • Energy to lift up an apple by one metre: 1 J • Energy to make the human heart beat once: ½ J • Energy to press key on computer keyboard: 1/100 J

  21. Learning Today • Potential Energy – Ep. • Homework Potential Energy Sheet due Thursday 12th January 2012 • Kinetic Energy – Ek • If you need to find me, I will usually be in my classroom SS15 or the science office SS3 • Next lesson I want to spend half the lesson building roller-coaster, you need your log on details.

  22. Ep m g h Potential Energy – Copy this Gravitational potential energy is the energy an object has because of its position in a gravitational field GPE = mass x height x Change in height Ep= gravitational potential energy J m = mass kg g = gravitational field strength N/kg h = height m Now make mass, gravitational field strength and height the subject of the formulae

  23. Ep m g h Rearranging the formulae

  24. Ep m g h Ep= gravitational potential energy (J) m = mass (kg) g = gravitational field strength (Nkg-1) h = height (m)

  25. Example Woof! (help!) A dog of mass 12 kg falls from an aeroplane at a height of 3.4 km. How much gravitational energy does the dog have as it leaves the aeroplane?

  26. Example On earth g = 10 m/s2 Mass of dog = 12 kg Height = 3.4 km = 3400 m

  27. Example On earth g = 10 m/s2 Mass of dog = 12 kg GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J Height = 3.4 km = 3400 m

  28. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J Just before the dog hits the ground, what has this GPE turned into?

  29. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J KE at bottom = 408 000 J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  30. Kinetic energy

  31. Some example questions… • How much gravitational potential energy have the following objects gained?: • A brick that weighs 10N lifted to the top of a house (10m), • A 10,000N car lifted by a ramp up to a height of 50cm, • A 70kg person lifted up 50m by a ski lift. • How much GPE have the following objects lost?: • A 2N football dropping out of the air after being kicked up 30m, • A 0.5N egg falling 10m out of a bird nest, • A 10,000N car falling off its 50cm ramp. • Mr Richards when bungi-jumping off a 110-metre high bridge in Zambia in August

  32. Energy changes

  33. Kinetic energy This is the energy possessed by an object due to its movement. What factors will increase the amount of kinetic energy a moving object has? The velocity of the object The shape of the object The mass of the object The height of the object  x  x

  34. Ek ½ m v2 Kinetic Energy Copy this Ek = kinetic energy J m = mass kg v = speed m/s

  35. Ek ½ m v2 Kinetic Energy Now make mass and velocity the subject of the equation Ek = kinetic energy J m = mass kg v = speed m/s

  36. Mass and speed If you increase the mass of a moving object you increase the kinetic energy. If you double the mass, you double the kinetic energy. If you increase the speed of a moving object you increase the kinetic energy. BUT… If you double the speed, you quadruple the kinetic energy. This is why even if you are slightly above the speed limit, you increase the kinetic energy of a moving car a lot, this means it is harder to stop the car and there is more chance of an accident.

  37. A car has a mass of 400kg and a velocity of 10 ms-1, what is the kinetic energy of the car? Kinetic energy calculation Kinetic energy = ½mass(velocity)2 = ½ x 400 x(10)2 = 20 000 J

  38. Example A bullet of mass 150 g is travelling at 400 m/s. How much kinetic energy does it have?

  39. Example A bullet of mass 150 g is travelling at 400 m/s. How much kinetic energy does it have? Ek = mv2/2 = (0.15 x (400)2)/2 = 12 000 J

  40. Using conservation of energy • Now with a falling object as it falls faster and faster the potential energy is gradually converted to kinetic energy. At the moment just before impact, potential energy is zero and all the potential energy has been converted to kinetic energy we can use this to solve problems and find the velocity

  41. Now a bit of algebra

  42. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J KE at bottom = 408 000 J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  43. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  44. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J KE at bottom = 408 000 J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  45. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J KE at bottom = 408 000 J = mv2/2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  46. Example 408 000 = mv2/2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  47. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  48. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 816000 = 12v2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  49. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 816000 = 12v2 68000 = v2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  50. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 816000 = 12v2 68000 = v2 261 = v v = 261 m/s Assuming no energy is lost as air resistance – in reality the dog would have reached TERMINAL VELOCITY

More Related