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# Weeks 1-2 Lecture Notes: Phys-P150 How Things Work PHYS-P150

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This 9 page Class Notes was uploaded by emma woodman on Tuesday January 27, 2015. The Class Notes belongs to PHYS-P150 at Indiana University taught by John Carini in Fall. Since its upload, it has received 218 views. For similar materials see How Things Work in Physics at Indiana University.

## Reviews for Weeks 1-2 Lecture Notes: Phys-P150 How Things Work

If emma isn't already a tutor, they should be. Haven't had any of this stuff explained to me as clearly as this was. I appreciate the help!

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Date Created: 01/27/15

PHYSP 150 How Things Work A phone is a transmitter and receiver of radio waves Different antennas with different bands for different radio frequencies More data stored in less space because of Moore s Law Phones have built in sensors to tell if they ve been dropped in the water Energy 0 The capacity for doing work When one object exchanges energy with another by exerting a force and produces a displacement Physics was one of the first things people tried to measure Lifting something 16 lbs it would have to be proportional How you lift something horizontally The way out of definitions in words we can define quantities in Physics by 0000 stating how to measure them the energy of a system is a quantity that can be calculated from measurable properties of the system the types of particles that make it up their speeds and their positions 0 Speed has to do with the amount of work The speed at any point of its motion or lowest point can be calculated by the height it started at 0 The original height and the lowest height can determine the equation 0 Galleleo determined some of the mathematical patterns 0 Chemical energy in sugars and fats that are converted into another energy to activate muscles 0 Gravitational potential energy I kinetic energy gravitational potential energy 0 Conservation law energy 0 By pushing the ball you are exerting extra energy 0 Making energy you can t do it I You can only convert it from one form to another 0 We usually have to pay for energy in a form easily converted into other forms 0 Storing Energy I We can say that matter has energy we usually focus on the useful portion of the energy the part it will readily give up I Examples of convertible forms of energy 0 Food or a battery has chemical energy 0 Wind has kinetic energy energy of motion 0 A hot object has thermal energy that it readily gives up to cooler objects 0 A wound spring or stretched rubber band has elastic energy 0 Mass is a form of energy a tremendous resovoire of energy 0 Thermal energy is useful when the thermal temperature is higher than the surrounding temperature If the temperatures are equal it is essentially useless Our Plan 0 O O 0 Almost everything in a cell phone uses electrical energy We need to understand energy and its electrical forms Batteries supply the electrical energy so we need to understand what makes them work Ultimately we find that the batteries limit much of what we can do with our portable devices Unites that measure energy 0 O O O O O calorie heat BTU heat Calorie food energy or chemical energy kilowatthour electrical energy electronVolt atomic or molecular energy Megaton nuclear weapons asteroid collisions Why are there so many ways to express energy 0 O 0 Many different forms of energy Often we measure those different forms in different ways To express the result the measured amount is compared to an appropriate standard unit For example I l calorie is the amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius A more familiar conversion 0 We can convert energy measured one way to an equivalent amount measured in a different unit 0 Currency conversion example 16685 US dollars I 1 British Pound 39 50 x l Pound16685 2997 pounds Energy Equivalents O l calorie 419 Joule used to measure thermal energy it is the amount of heat needed to raise temperature of 1 gram of water by 1 degree Celsius O l Calorie l kilocalorie1000 calorie 4186 Joule O l poundfoot used to measure work in the English system 0 l watthour 3600 Joules O 1 kilo watthour 3600000 Joules 39 50 calorie cookie 0 50 calories x 4186 J oules l calorie 209300 J I AA battery 42 watthours 0 42 watthours x 3600 J oules l watthour 15120 J 0 Kinetic Energy all matter has it I Kinetic Energy 12 X mass X speed2 I If mass is measured in kilograms and speed in metersecond then KE is in joules 0 Generating amp Using Electric Energy 0 O 0 Kinetic Energy wind turbines convert the kinetic energy of moving air Light Solar cells are used to generate electricity directly Heat coal and gasfired power plants burn their fuels to generate steam to drive electricity generating turbines Gravitational Energy hydroelectric plants convert gravitational energy to kinetic energy of the water to drive a turbine Chemical energy a battery converts stored chemical energy that is released by the passage of electrons between the battery s terminals Nuclear Energy nuclear plants convert energy stored in the mass of heavy nuclei to heat which is converted to steam 0 Convert electrical energy into mechanical energy and then into light I As long as theirs a temp difference between top plate and bottom plate ithe wheel will keep spinning I Work and Power 0 0 Energy is a property of an object or system Work is when energy is transformed or transferred when a force causes motion or change work is not a property of something it measures a process Power is the rate that energy is converted for example how fast work is being done I Power work time 0 If we know Power and Time we can calculate how much work is done 0 Work Power X time I Terms that apply to power 0 O O 0 Watt kilowatt10quot3 Watt MegaWatt10A6 Watt Horsepower 746 Watt BTUhour Anything with a unit of energy in the numerator and a unit of time in the denominator represents a power KiloWatt hour means KiloWatt X hour which is a power 0 Power that is involved in different activities 0 O 0 Cell phone 1 Watt Laptop Computer 10 Watt Incandescent light bulb 40150 Watt 00000 0 LED or uorescent bulb equivalent 830 Watt Person at rest 25 watt Person exercising heavily 500 Watt Kitchen appliances 1000 Watt Auto Engine 240 hp 180000 Watt180 kilowatt Train diesel locomotive 4400 hp 3200000 watt 320 kilowatt 0 Energy conversions with power 0 00000000000 000 0 Power Energy convertedTime Watt J oule seconds Energy Converted Power X Time Time Energy converted power Watt J oule seconds Kilowatt1000 watts 1 horsepower 746 watts Power x Time Energy converted KiloWatt X hour 1000 J ouleseeends3600 seeends3600000 Joules Energy Power X Time 05 Watt X 12 hours 6 watt X hoursW H 6 watt X hour 6 J ouleseeends X 3600 seeends 21600 Joules When you multiply a power in Watts by an amount of time that represents an amount of energy transferred If power is expressed in watts and time in seconds the energy converted is expressed in Joules For example recall 1 hour3600 seconds 1000WaM hour1000 J oulesecond 3600 second3600000 Joule A cellphone requires 05 WaM of electrical power to run How much energy is required to run it for 12 hours express in WaMhours Joules and Calories Energy needed Power required X Time Energy 05 WaM X 12 hour 60 WaMhour 60 WaMhour3600 secondshour21600 WaM second21600 Joule 21600 J oule 1Calorie4186J oule50 Calorie 0 Examples 0 O A 100 Watt light bulb stays lit for 8 hours how much electrical energy expressed in Joules is used I Energy Power X Time I Power 100 Watt 100 J ouleSecond I Time 8 hour X 3600 second1 hour 28800 seconds I Power x Time 2880000 Joule 288 Megajoules A runner burns 800 Calorie in an hour what is the power in Watts I Power EnergyTime 800 Calorie1 hour I Energy800 Calorie x4200 J oule1Calorie336000 Joule I Time lhour X 3600secondhour3600seconds I PowerEnergyTime 336000 J oule3600seconds 933 J oule second93 3WaMs Energy or Power 0 200 Calories per hour I Power 0 57 watt X hours I Energy power watt times a time hours represents an amount of energy 108 Kilowatt X hours is 0 An amount of Energy watt measures power and hours measure time therefore power X time Energy and power example 1 0 000 O The Chevrolet Volt is an electrically driven car with a lithium battery pack that provides 108 kilowatt X hour of electrical work How many miles can it take you We need to convert to megajoules 1 megajoule10quot6 Joules to find out how many miles we can drive Recall from last time that 1 kilowatt X hour 36 MegaJoules 108 X 1000 X Joulesecond X 3600 second 108 kilowatt X hour X 36 Megaj ouleskilowatt X hour 108 X 36 megajoules 388 miles Energy and Power Example 2 O O O A cell phone battery stores 75 watt X hours of chemical energy If you have a charger that can supply 25 watts of electrical power how long will it take to charge the battery Energy needed 75 Watt X hours Time Energypower 75 watt X hours25 watt 3 hours Efficiency Useful Energy Output Total Energy Input 0 Electrical energy can often be converted at nearly 100 into other forms heat mechanical work chemical energy Chemical energy can be converted into heat nearly 100 efficiently but not so well into other forms I Gasoline cars are 20 efficient in converting the chemical energy in gas to kinetic energy I Humans are up to 25 efficient at converting chemical energy into mechanical work I Electric power plants are up to 45 efficient at converting the chemical energy in coal into electric energy I Fuel cells can be up to 75 efficient in converting chemical to electrical energy I Electric motors can be over 90 efficient at converting electrical to mechanical energy Efficiency example with a conversion 0 A kilogram kg of coal contains approx 6000 calories of chemical energy Suppose it can be burned to produce electric energy with an efficiency of 40 How much coal does it take to produce 1 kilowatt X hour of electric energy 6000 CalorieKg4186 J oulesCalorie 25 Mega joulesKg Electrical energy out Efficiency X Energy Input I 40 X 25 Mega jouleskg 10 Mega jouleskg Electric Energy Generated I 1 kilowatt X hour 10 mega jouleskg 36 Mega joules 10 mega jouleskg 036 kg Sufficient Power 0 Sufficient power means that energy can be converted quickly when needed 0 How intense is sunlight Its on a kilowatt 1 meterx 1 meter 1000 joules per second If one square meter is 1000 watts make it 10 X less on both sides 10 cm by 10 cm would generate 1 watt and therefore a phone but it s not practical for continuous use Electric Charge 0 Electric charge is a property of the elementary particles that make up matter 0 Charge is quantized it comes in integer multiples of e the elementary charge 0 Charge is conserved has to be equal amounts of positive and negative charge 0 Protons carry positive charge e electrons carry negative charge e in ordinary matter these are the only two particles contained in ordinary matter that have nonzero charge neutrons are neutral zero charge exactly 0 Charge is measured in units called the coulomb O E 160 X 10quotl9 Coulomb O l Coulomb 62 X 10quot18 e Electric Force 0 The most important force to our lives 0 You have to do work to pull positive and negative charges apart 0 Because the forces are strong you can store a lot of energy electrically 0 Electric force makes charges of opposite signs attract similar signs repel Mobile electric charge O 0 Sources of electric energy make charges want to move apart or through a circuit Most charge is tightly bound to opposite charges but some charge is mobile I Electrons in metals like aluminum and copper I Ions dissolved in liquids electrolytes like our blood or seawater or between the electrodes in a battery There are only two main types of electric charge positive and negative Ions are atoms that are missing or have electrons added to them Ions are neutral when it has 11 protons and 11 electrons Sodium electrons 11 protons and 10 electrons O 11e 10e e Matter with mobile charge is called a conductor Matter with only a tightly bound charge is called an insulator O Insulators do not conduct electricity Semiconductors are in between they can be made conducting or insulating in a variety of ways 0 O O Chemically adding particular types of atoms Electrically as in the most common device on the planet the FET or field effect transistor Using light photoconductivity Most common example silicon The variety of methods of making semiconductors conduct is responsible for their usefulness Flow of charge 0 Generally charge does not like to build up it ows 0 It ows in a circuit or path 0 The circuit or path must be closed in order to move 0 Flow of charge is measured as the rate of ow past any point in the circuit Current ChargeTime 0 Time ChargeCurrent 0 International unit of current is the Amp I 1 Amp 1 Coulombsecond 0 Example 300 Coulombs moves through a wire in 60 seconds What is the average current I Current 300 Coulombs60 Seconds 5 Amps Analogies of Charge Flow 0 Charge Coloumb 0 Current ColoumbSecond 0 Voltage Volts 0 Electric Power current X voltage watt 0 Battery or generator 0 Switch we close a switch to make current ow Analogies of Fluid Flow Voltage electric energycharge 1 Volt 1 JouleCoulomb If the same amount of charge ows from a battery which battery provides the most work 0 A small 9 Voltbattery O A large6 Volt battery 0 A huge 45 Volt battery I A small 9 volt battery even though it s small it exerts more charge Electric energy voltage X charge 1 watt 1 volt X 1 amp Examples 0 3 amps of current ows in a circuit with a 6 volt battery How much electric power is provided 39 6 Volts X 3 Amps 18 Watts 0 A 60 watt light bulb is designed to be connected to a 120 Volt source what is the current 39 Current PowerVoltage 60 watt 120 Volts050 amps The law of conservation of energy states that energy cannot be created or destroyed It may however be either transferred from one object to another or changed from one form to another A possible example in our everyday lives would be seeing a moving car hit a stationary or parked car causing it to move The energy in the moving car was transferred into the parked car Energy conversion is the process of transforming energy from one form to another One example I experienced today was turning a car on By turning on the car it changes chemical energy from fuel to thermal energy and mechanical energy By toasting my bread this morning I experienced the toaster converting electrical energy to thermal energy When speaking to my parents today on the phone the sound energy of my voice was converted into electrical energy in the phone and then converted into sound energy on their phone allowing them to hear me When turning on the television in my room I experienced electrical energy being converted to sound and light energy as images emerged on the screen The last and final example I experienced today was seeing a biker get on his bike and begin to ride This is an example of stored potential energy converted into kinetic energy

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