GUIDED GROUP

 LESSON C: traditional lesson groupGUIDED GROUPSummary TOC \h \u \z 1. What is energy? Work, and power? Some definitions to start with.. PAGEREF _gjdgxs \h 43. Where is energy? Which forms does it assume? PAGEREF _bcl6bmovbqf7 \h 4Let us have a look to the picture below. Let us learn some new names in the light violet ovals. PAGEREF _ox9q97u65bbq \h 54. Energy in potential and in motion PAGEREF _pzdazlchz8go \h 55. SOME FORMULAS: INSIDE THE HIGHER PHYSICS: KINETIC ENERGY PAGEREF _fqai4rfo7i2f \h 66. Potential Energy: a way to store energy. PAGEREF _wgggukfdltb8 \h 77. Energy in everybody life and sports: exemples PAGEREF _wxk0ibg9o2ad \h 78. ENERGY Transformations. Exemples PAGEREF _b42slajk0daz \h 79. Conservation of energy: an important property PAGEREF _quyo43rz68r \h 1110. Energy and life and sports: exemples, what about you? Food [SS8] and energy PAGEREF _frhgz440b9as \h 12EXERCISES : PAGEREF _e1r208tk05ct \h 13YOUR OBJECTIVE IS LEARNING AND UNDERSTANDING THE FOLLOWING TOPICS TO BE ABLE TO ANSWER SOME QUESTIONS YOU ARE GOING TO LISTEN TO A TEACHER LED LESSON, YOU WILL HAVE BOOKS, WEBSITES AND ANY KIND OF HELP, TO UNDERSTAND THE TOPICYOU CAN ASK ANY QUESTION YOU LIKE TO THE TEACHEREVERYBODY WILL BE ASKED TO ANSWER ALL THE QUESTIONS ALL OF YOU WILL DO A TEST ON THE SUBJECT (FRIDAY)REMEMBER!! BE AWARE OF YOUR FEELINGS AND THOUGHTS DURING THE LESSON, SINCE YOU WILL BE ASKED TO TELL US YOUR OPINION BY FILLING A SURVEY ON TEACHING METHODOLOGY. TOPICS - At the end of this lesson you are expected to know how:· define work, energy , power· know the right units of measure of physical dimensions (force, distance, speed, velocity, heat, energy, work, power, mass, highness..)· recognize different forms of energy· write the expression for KINETIC and POTENTIAL GRAVITATIONAL energy · understand the law of energy conservation· find different forms of energy in daylife situations, in some sports, in industrial activities· understand and recognize energy transformations in daylife situations, in some sports , in industrial activities· compute the amount of kinetic energy in some moving masses, and the Potential gravitational energy in some situations· find the estimated number of calories when you do some physical exercisesQUESTIONS: find answers to these questions TO BE PROPERLY prepared to your final test1. What is energy? Work? Power? Give A definition..2. What is Potential Energy? Show at least TWO practical examples in which we can identify it Where is ENERGY? Which forms does it assume?3. What is Kinetic energy? Where do you find it?4. Energy in everybody life: which forms of energy do you know now? Recognize them in given situations (SOME EXAMPLES, SITUATIONS ETC..)5. Transformations. How energy changes its form. Describe some transformations in the given examples. Give some examples of your own experience.6. Which is the very important property of energy? ( Even if energy changes its forms, it is always ...)7. Energy and sports[SS3] : which kind of energy do you find in sports? give examples,8. what about you? Which sport do you practice, if one? Which forms of energy do you find in your sport?9. Food and energy: [SS4] compare different activities and choose the more energy expensive one10. How many calorie[SS5] s do you need to ...... (run at .., walk to the top of a mountain.. etc..) read and understand some tables of comparison.11. Units of measure: equivalences between different units [SS6] (metres and kilometres, Joules and Calories, km/h, m/s, mph) CONTENTS1.What is energy? Work, and power? Some definitions to start with... What is energy? Energy is the capability to do some work.. And what is work? We do some Work , when we make something move using a force. For instance, please follow the instructions!- Push your book on your desk- Pull your backpack or schoolbag up from the floor to your chair- Hold your rubber in your hand and then let it fall down (see below...)- - (In couples) let the first of you two lie down on the ground, and the other grab his/her legs GENTLY and pull him/her SLOWLY AND SAFELY.WE ARE DOING WORK, because we are moving something (book, bagpack, friend) from a place to another, applying a force (pushing or pulling). Also the rubber is moved by a force: its own weight pulls it down.We measure work in JOULE symbol J. You will find a tiny biography of this extraordinary physicist here[1].We can do this work, because of some form of energy we have.Let us go further....2. Ehm.. what about POWER??Power is the rate of work done in a certain period of time, for instance some work in a second.In formula Power = work/ time unit of measure WATT (W)3.Where is energy? Which forms does it assume?Energy is everywhere, but it is hidden in such a huge amount of forms, that it is hard to believe!Let us have a look to the picture below. Let us learn some new names in the light violet ovals.And what about the energy that makes our electrical devices work for us?? Where does come it from? Some are in the exercise below.EXERCISE: Here are some examples: let us recognize the previous forms in the next page pictures. Complete...(In some cases more than one might match)2316882314325TIDAL: ................................. WAVE : : ................................. WIND : : ................................. SOLAR: : ................................. NUCLEAR: : ................................. BIOMASS: : .................................GEOTHERMAL: : .................................HYDROELECTRICAL: : ................................. COAL: : ..........................................4.Energy in potential and in motionWe can divide all the forms of energy in two main groups: POTENTIAL AND KINETIC. Here is an useful scheme to help ourselves to understand. The left side group is a way to store energy: that’s what POTENTIAL essentially means.Let us read and discuss this table. Then, fill in the spaces below.What have the right side forms have in common? .........................................................What does KINETIC mean? .............................................................................................. LET US CHECK! ......... ..... 5.SOME FORMULAS: INSIDE THE HIGHER PHYSICS: KINETIC ENERGYSince KINETIC deals with movement, even a simple falling raindrop has its own kinetic energy. It must involve some characteristic of motion, such as speed, and of bodies, such as mass. But in which way? Laws of physics help people to understand our entire World and Universe. Yet, some laws are so simple! As an example, here is the formula for the kinetic energy: Kin = 0.5 * mass* velocity 2 . At the end of these lessons you’ll find some exercises…6.Potential Energy: a way to store energy.Another useful and easy formula to compute energy:Potential gravitational energy = mass* gravitational acceleration g* highness = m*g*hWhat does it mean?- The mass is multiplied by a constant that depends on the position:- g is the gravitational acceleration: it is about 9.8 m/s2 on Earth. If we go to the Moon, or to another planet, the law is the same (power of physics!) but the number g changes.- Then we multiply by the highness of the position: the highest the mass is, the highest the energy it owns. Simple!Now we can do some exercises, and measure our own energy in some common situations.GO to the end to find out some exercises.7.Energy in everybody life and sports: exemplesNow we are ready to recognize energy in our daylife and in sports we practice : COMPLETE THE LIST at point 10._________8.ENERGY Transformations. ExemplesLet us have a look to these pictures: they show an important behaviour of ENERGY .ENERGY CHANGES ITS FORMSFROM ONE TO ANOTHERIN MANY DIFFERENT WAYS! We know the names of these forms of energy now. And even how they change from one to another to another to another.....Look at next scheme: it is very interesting and rich in information!What about our contribution in these continuous exchanges?? Some descriptions below help you understand how these transformations take place.Let us read some more!Energy TransformationsAn energy transformation is the change of energy from one form to another.Energy transformations occur everywhere every second of the day.Energy Transformations Examples1. A toaster transforms electrical energy into thermal energy.2. A blender transforms electrical energy into mechanical energy.3. The sun transforms nuclear energy into ultraviolet, infrared, and gamma energy all forms of electromagnetic energy.4. Our bodies convert chemical energy from food into mechanical and electrical energy to allow us to move.5. A natural gas stove converts chemical energy from burning into thermal energy used to cook food. Some other examples will help us understand another bit of our nature.Electrical Energy to Thermal Energy ConversionsElectrical energy is a form of energy that occurs as a result of either stored or moving charged particles. When the energy is stored it is called electric potential energy and when it is moving in an electric current it is a form of kinetic energy. Our most common form of electrical energy is found in our wall outlets. Thermal energy is energy that results from moving atoms or molecules and is commonly referred to as heat. The faster the atoms or molecules move, the more heat or thermal energy they have. In these examples we will be exploring instances where electrical energy is converted into thermal energy for use.Examples of Electrical Energy to Thermal Energy Conversions:1. A toaster draws electric current (electrical energy) from a wall outlet and converts these moving electric charges into heat (thermal energy) in the filaments that turn red hot to cook your toast.2. An electric clothes dryer turns electrical energy from a wall outlet into heat (thermal energy) to dry your clothes as they spin.3. A hair straightener turns the electrical energy from a wall outlet into heat (thermal energy).4. As electricity runs through the filaments in a space heater, the electrical energy is converted into heat (thermal energy).5. An electric stove plugged into a wall outlet uses the electrical energy to flow into the burners on the stove top and as the electric charges pass through the burners the electrical energy is converted into thermal energy.6. Although used for light, an incandescent light bulb produces mostly thermal energy (they get very hot) as it turns electrical energy into light by passing the electric charges through a very tiny filament.And more...Chemical Energy Transformations to Thermal EnergyChemical energy is a potential form of energy that is stored in the chemical bonds that hold atoms together. If bonds are broken, the energy is released, and if bonds are formed, energy is absorbed. Thermal energy is often referred to as heat energy. As molecules move faster and gain kinetic or moving energy, the temperature of the substance increases. During conversions from chemical energy to thermal energy, the energy stored in the chemical bonds are released and this energy causes surrounding molecules to move faster thus increasing the thermal energy of a substance.Examples of Chemical Energy to Thermal Energy:1. Coal is burned at a power plant. The chemical energy released as the coal is burned heats water and turns it into steam. The chemical energy causes the liquid water molecules to move faster increasing their thermal energy.2. Gasoline is burned in a car engine. As the gas burns, small explosions release heat or thermal energy which makes the pistons move so the car go.3. A furnace burns natural gas in a chemical reaction. As the natural gas burns, heat is released causing air molecules to move faster. The temperature of the air increases because they have more thermal energy which is used to heat a house.4. Hand warmers used for hunting operate by chemical reaction. When the contents of the bag are mixed together, a chemical reaction causes chemical bonds to break releasing energy. This energy causes the thermal energy of the solution inside the bag to increase and we feel heat to warm our hands.5. A butane torch burns butane gas. As the chemical bonds are broken during the reaction, heat is released. The heat is used to increase the thermal energy of a metal which melts and is used to weld pipes together.And at the end, a very good and clarifying scheme: 9.Conservation of energy: an important property There are many different forms of energy such as electrical, thermal, nuclear, mechanical, electromagnetic, sound, and chemical.All these forms follow a very important and simple law:THE LAW OF CONSERVATION OF ENERGY It states that energy is always conserved in the universe and simply changes from one form to another, many energy transformations are taking place constantly.Therefore, even if transformations take place everywhere and in every moment, the energy we had at the very beginning is always the same.A numerical exercise: Tom and Anne ate their cornflakes and milk at breakfast. They took 1000 Joule chemical energy each . So they use their amount of energy to move, wash their teeth, take their books, go to school, for instance walking or cycling, speak, run, walk and have their food digested. Some of their energy goes in heat.But at the end the total amount of energy in transformations is equal to 1000 Joule.Another example: if you want to throw a 1 kg ball from the ground level to a 2 m high shelf, you must give your ball a beginning kinetic energy at least equal to the potential energy the ball would have at that highness.Try to complete the exercise by yourself![SS7] Potential energy = ....................................................= ..................................................= .......... J[2]. 10. Energy and life and sports: exemples, what about you? Food [SS8] and energy We are at the end of our small journey.Now you should be ready to answer without help...a)Which kind of energy do you recognize in these sports? Why?Fill the following list:- here: ....................................................................................................................................- at home,................................................................................................................................- travelling by car, ...................................................................................................................- walking: ...............................................................................................................................- studying:..........................................................................................................................- eating: ..............................................................................................................................- playing soccer, .................................................................................................- playing tennis, ..... .................................................................................................- skiing: ................................................................................................................................- jogging .....................................................................- playing volleyball, basketball....................................................................................- what about you? Think of some personal situations and analyze them! . ................................................................................................................................................................................................................................................................b)Transform a speed of 10 km/h in m/s. ......................................................................[3]c)Compute the ............................... energy of your friend (mass = 68 kg) running at a speed of 10 km/h :...................................................................................................................................[4]d)Transform in Joules the chemical energy of a sandwich (250 kcal) ........................................................................................... [5] EXERCISES : Here are some exercises to prepare your final test. Some of them are completely solved, others are for your training.Solutions are provided at the end.Have fun!1.sometimes we need to convert km/h in m/s speed, since the formula for kinetic energy wants only metres and seconds. How can we do that?DATA:v= 30 km/hWe want it in m/s. The technique is:v= 30 km/1 h (30 kilometres in 1 hour) = 30*103 m/ 3.6*103 seconds = = 30/3.6 m/s =8.3 m/sQuite easy, isn’t it? we simply transform km in metres, and hours in seconds and divide the result.There is a very simple way to solve the riddle: can you guess it? Try by yourself and check it in the note[6] 2.a car is running at a speed of 30.0 m/s. its mass is 1,200 kg (1.2 tons). Therefore its .................. ... energy is .........................................DATA:v= 30.0 m/s is the speedm= 1,200 kg (one thousand two hundreds of course!) is the massThe only form of energy we can try to compute is kinetic energyTherefore, we use the formula Ke = = 0.5*1200 kg*(30 m/s)2 == 540 000 = 5.4*105 JTherefore its KINETIC ... energy is = 5.4*105 JRemember the final measure unit J, and write the number in scientific notation.The power (30 m/s)2 is to be computed before the multiplication.. Now compute the kinetic energy for a dog (4.5 kg) running at 5 m/s, a Boeing 747 airplane (333 390 kg) flying at the speed of 800 km/h, a horse (450 kg) galopping at 65 km/h.(dog running : 0.5*4.5 kg*(5 m/s)2 = 56.25 J)(Boeing flying : 0.5*3.33*105 kg *(800/3.6 m/s)2 = 8.22*109J)(horse galopping : 0.5*450 kg*(65 /3.6 m/s)2 = 7.34*10 4 J)3. from the table below, we find some bike racers speeds.Transform the following speeds from mph (miles per hour) to km/hV1 = 10 mph = ........V2 = 12 mph = .......V3 = 16 mph = .........V4 = 25 mph = ...............DATA:V = 10 mph speedRemember that 1 mile = 1,61 km,Therefore we can solve an easy proportion1 mile/h : 1,61 km/h = 10 miles/h : X km/hX km/h = 1,61 km/h *( 10 miles/h )/ 1 mile/h =16,1 km/hIt is very simple! Just multiply your speed by 1,61!Some bikers are very quick, aren’t they?4. Now let us know how to compute potential gravitational energy. Remember : it is fundamental for electricity production AND FOR SKIING AS WELL! . A cat is climbing a tree. The tree is 5.0 m tall, and the cat weighs 1.5 kg. Therefore his .................. ... energy is .........................................DATA:m= 1.5 kg cat’s massh=5.0 m final positionThis energy is simply U= m*g*h = 1.5 kg*9.8 N/kg*5.0 m = 73.5 JWe use the number g=9.8 N/kg as the gravitational acceleration. It depends on the planet. On the Moon, it is very low, about 1.6 N/kg. It means that you would jump higher than an olympic champion!!.Which formula is used on another planet? Try to guess the answer and then check at the note[7]. 5. Tom is on the top of a ski run, 1.5 km high. Tom is 85 km heavy .- find his potential energy. - When at the end of the run, how much maximum kinetic energy could he have?DATA:m= 85 kgh=1.5 km = 1.5 *103 mTo find the potential energy U= m*g*h = 85 kg*9.8 N/kg*1.5 *103 m= 1.25 * 10 6 J.Lot of energy!How much kinetic energy?If there is nothing to disturb his motion, his energy is preserved according to the principle of energy conservation, therefore he should have the same amount of energy:= simply 1.25 * 10 6 J.. Yet lot of it gets lost due to frictions, air and snow interactions.... 6. Computing calories.Look at the tables below and ask yourself how much energy an athlete is consuming during his performances.. a tennis complete game lasts a variable time but some computations give an average time of 2 hours and half . how many calories do the players consume?DATA:C= 6.35 Calories /minuteT=2 hours and half = 2h*60 minutes/hour+30 minutes = 150 minutesLet us multiply our dataTotal amount of energy = C*T = 6.35 Cal/min*150 min = 950 Calories= kilocaloriesIt seems not to much, but remember they are GREAT CALORIES,1 Cal = 1 k cal (kilo calorie= 4 186 J! )So, 950 Cal = 4*106 J 4 millions of Joules! Quite a lot!Look at your snack: there are lot of information, and the main one is the ENERGY, given in kJoules and in Calories or kcalories. [1] James Prescott Joule, (born December 24, 1818, Salford, Lancashire [now in Greater Manchester], England—died October 11, 1889, Sale, Cheshire), English physicist who established that the various forms of energy—mechanical, electrical, and heat—are basically the same and can be changed, one into another. Thus he formed the basis of the law of conservation of energy, the first law of thermodynamics.Joule studied with the noted English chemist John Dalton at the University of Manchester in 1835. Describing “Joule’s law” in a paper, On the Production of Heat by Voltaic Electricity (1840), he stated that the heat produced in a wire by an electric current is proportional to the product of the resistance of the wire and the square of the current. In 1843 he published his value for the amount of work required to produce a unit of heat, called the mechanical equivalent of heat. He used four increasingly accurate methods of determining this value. By using different materials, he also established that heat was a form of energy regardless of the substance that was heated. In 1852 Joule and William Thomson (later Lord Kelvin) discovered that when a gas is allowed to expand without performing external work, the temperature of the gas falls. This “Joule-Thomson effect” was used to build a large refrigeration industry in the 19th century. The value of the mechanical equivalent of heat is generally represented by the letter J, and a standard unit of work is called the joule. [2] U g = m*g*h= 1 kg*9,8 N/kg*2 m= 19,6 J of potential energy. You must throw your ball at a minimum speed of 6,3 m/s! not bad![3] 10 km/h = 10/3,6 m/s = about 2,8 m/s[4] Kinetic en = 0.5*m*v2= 0.5*68kg*(2,8m/s)2 = 262 J remember! First velocity at the power of 2! After that, multiply the result by the mass![5] Quite simple = energy in Joule is energy in kcal*4,186 kJ/kcal = 250 kcal*4.186 J/kcal = 1.046 * 10 3 kJ =[6] To transform from km/h to m/s just DIVIDE BY 3.6! to transform from m/s to km/h just MULTIPLY BY 3.6![7] . WHICH POTENTIAL ENERGY ON OTHER PLANETS? The same formula, OF COURSE, but with a different constant g! ................
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