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UNIT 2 Energy Flow in Technological Systems 1 Steam Engines a boiler generates steam and a steam engine converts the steam pressure into mechanical motion 1698 Savery in England received the first patent for a steam engine to help remove water from mines Pg 142 2 Steam Engines continued 1712 Newcomen invented a much improved steam engine Pg 143 1757 James Watt modified the design of the steam engine so eventually it became useful in many industries – Industrial Revolution 1884 Charles Parsons perfected the steamturbine engine – no pistons steam-turbine engines still today power giant ocean liners and cruise ships 3 Scientific Theories of Heat 1. Phlogiston Theory substances that could burn contained an invisible fluid – phlogiston 2. Caloric Theory caloric or heat was a massless fluid that was found in all substances 4 Scientific Theories of Heat caloric could not be created nor destroyed but could flow from one substance to another caloric always flowed from warmer objects to cooler objects J Black defined a unit of caloric – the calorie 1 cal was the quantity of caloric that would increase the temperature of 1 g of water by 1ºC 5 Scientific Theories of Heat 3. Modern Theories Count Rumford suggested that there is no substance such as caloric, he believed that there was a relationship between mechanical energy and heat Mayer a German doctor discovered that heat is related to energy 6 Scientific Theories of Heat Joule a British physicist was given the credit for discovering the mechanical equivalent of heat The SI unit for energy, the joule is named in his honour 7 Energy is the ability to do work 8 Work is the transfer of mechanical energy from one object to another is a push or pull on an object that results in motion in the direction of the force applied 9 Work W=FΔd W= work in joules(J) F= force in newtons(N) Δd= distance in metres 10 Law of Conservation of Energy Energy cannot be created or destroyed, but it can be converted from one form to another 11 Calorie Today the calorie is defined as the amount of energy that must be added to 1.0 g of water to increase its temperature by 1.0 ºC 1 cal = 4.186 J 12 Heat and Thermal Energy kinetic energy – energy of motion the greater the kinetic energy of a substance the faster the particles of the substance are moving around – kinetic molecular theory heat is now defined as the transfer of thermal energy from one object to another heat and work are mechanisms by which energy can be transferred from one object to another 13 Specific Heat Capacity is the amount of heat required to raise 1.0 g of a substance 1ºC is different for every substance symbol is ‘c’ units are ‘ J/g ºC’ 14 Temperature is a measure of the average kinetic energy of the individual atoms or molecules in a substance 15 Thermodynamics is the field of physics that deals with forces and motion involving heat(the transfer of thermal energy) 16 Thermodynamics continued 1. First Law of Thermodynamics Energy cannot be created or destroyed, but can be transformed from one form to another or transferred from one object to another 17 Thermodynamics continued 2. Second Law of Thermodynamics It is not possible for any process to remove thermal energy from an energy source and convert it entirely into work No process can be 100 % efficient. Some energy will always remain in the form of thermal energy 18 Thermodynamics continued Lost as heat Thermal energy always flows from the warmer object to the cooler object 19 Internal Combustion Engines fuel is burnt inside a cylinder the hot gases expand and push the piston down the cylinder modern engines have 4, 6, or 8 pistons all attached to the same crankshaft these pistons are designed to fire at different times 20 Internal Combustion Engines at least one piston is always in its’ power stroke examine diagram Pg 165 the internal combustion engines release greenhouse gases and gases that contribute to smog and acid rain 21 Production of Electrical Energy all commercial electrical energy is produced by electrical generators electrical generators have huge magnets with coils of wire of wire turning between the poles of the magnets in most generators turbines turn the coils kinetic energy of the coils is converted into electrical energy 22 Production of Electrical Energy steam pressure drives the turbines for 1/3 of the electrical energy produced in Canada the heat that boils the water comes from the combustion of fossil fuels or nuclear reactions hydro-electric generating stations produce 2/3 of the electrical energy 23 Production of Electrical Energy the pressure of the water behind the dam forces the turbines to turn a few places in Canada are able to make use of wind energy to produce electrical energy 24 Measuring Motion quantities that describe magnitude but not direction are called scalar quantities speed, distance and time are scalar quantities quantities that include direction as well as magnitude are vector quantities velocity, displacement and position are vector quantities 25 Distance vs Displacement distance is measured along the actual path travelled displacement is measured along a straight line joining the initial and final positions adding vectors head to tail allows you to calculate displacement in two dimensions adding vectors along a straight line allows for calculating displacement in one dimension (directions N,S,E,W or +/-) 26 Speed vs Velocity both quantities involve time time(t) is a point in time time interval(Δt) is the difference between two times speed is the distance travelled by an object during a given time interval divided by the time interval 27 Speed vs Velocity continued v = Δd Δt velocity is the displacement of an object during a time interval divided by the time interval v = Δd Δt 28 Speed vs Velocity continued as speed or velocity may change during an interval of time the above formula represent the average speed or velocity Converting km/h to m/s 29 Uniform Motion the velocity is constant on a Distance-Time Graph the line is a straight line(horizontal or slanted) Slope = rise run Slope = velocity **When a position vs time graph is a straight line the velocity is constant. 30 Acceleration a change in velocity during a time interval (speeding up or slowing down) is a vector quantity a force is required to change motion in some way 31 Acceleration continued units for acceleration are m/s2 (5m/s2 means the speed is changing at 5m/s every second) formula is a= ∆v t ∆v= change in speed t = time in seconds a = acceleration (m/s2) 32 Acceleration continued ∆v = vf - vi vf = final speed (m/s) vi = initial speed (m/s) a = vf - vi t 33 Graphing Accelerated Motion a position time graph for acceleration is a curved line as the speed is changing when speed increases the graph curves upward when spedd decreases the graph curves downward a velocity time graph of uniform acceleration is a slanted line. 34 Kinetic Energy is the energy of motion the amount of KE an object has depends upon its speed and its mass KE or Ek = 1/2mv2 or mv2 2 35 Kinetic Energy continued Ek = kinetic energy in joules (J) m = mass of the object in kilograms(kg) v = speed in metres per second (m/s) 1 J = 1 kg m2 s2 36 Potential Energy is the stored energy it has the potential to do work many forms of PE eg. elastic, chemical, nuclear, electrical and gravitational 37 Gravitational Potential Energy is the energy an object has due to its position above the earth’s surface or some other point of reference (a table) for an object to posses Peg work must be done on it Thus ‘work and energy’ are equivalent 38 Potential Energy continued PE or Ep = mgh m = mass in kg g = 9.81 m/s2 h = height in m PE = potential energy (J) W = Fd = Fgd = mgh h=? m=? 39 Weight ***Weight is a force Fg = mg units for weight are N (kg m/s2) 40 Efficiency of Energy Conversions Efficiency is a measurement of how effectively a machine converts energy input into useful energy output the energy that perform the task is called useful energy some energy is always lost – usually as heat 41 Efficiency of Energy Conversions efficiency = useful output energy x 100% total input energy Second Law of Thermodynamics “No process can be 100 percent efficient. Some energy will always remain in the form of thermal energy”(wasted energy) 42 Energy Efficiency and the Environment every time there is an energy conversion some energy is wasted in the form of heat example – hydro-electric generating stations are 70% efficient while coal burning stations are 35% efficient 43 Energy Efficiency and the Environment businesses and industry are the largest consumers of energy and so it is important that they use energy efficiently many companies have already installed more energy efficient lighting, heating and cooling equipment to conserve energy 44 Energy Efficiency and the Environment all sectors of society must become conscious of the problems and search for solutions the solutions must be sustainable a sustainable process will not compromise the survival of living things or future generations while still providing for our current needs 45 Energy Efficiency and the Environment another less obvious method is to encourage industries to use cogeneration cogeneration is the process of using waste energy from one process to power a second process eg. in a thermal power station, the steam that is used to turn the turbines could then be used to heat local buildings 46