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## Work in addition to Energy Physics 100 Chapt 5 Physicists definition of work dist Work =

Wolfson, Kate, Executive Producer has reference to this Academic Journal, PHwiki organized this Journal Work in addition to Energy Physics 100 Chapt 5 Physicists definition of work dist Work = F x dist A scalar (not a vector) dist Atlas holds up the Earth But he doesnt move, dist = 0 Work= Fx dist = 0 He doesnt do any work!

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Garcon does work when he picks up the tray but not while he carries it around the room dist is not zero, but dist is 0 Why this definition Newtons 2nd law: F=m a Definition of work + a little calculus Work= change in ½mv2 A scalar equation A vector equation This scalar quantity is given a special name: kinetic energy Work = change in KE This is called: the Work-Energy Theorem

Units again Kinetic Energy = ½mv2 kg m2 s2 work = F x dist N m =kg m s2 m =1Joule same! Work done by gravity start end dist dist W=mg Work = F x dist = -mg x change in height = -change in mg h change in vertical height Gravitational Potential Energy Workgrav = -change in mgh This is called: Gravitational Potential Energy (or PEgrav) Workgrav = -change in PEgrav change in PEgrav = -Workgrav

If gravity is the only as long as ce doing work . -change in mgh = change in ½ mv2 0 = change in mgh + change in ½ mv2 change in (mgh + ½ mv2) = 0 mgh + ½ mv2 = constant Work-energy theorem: Conservation of energy mgh + ½ mv2 = constant Gravitational Potential energy Kinetic energy If gravity is the only as long as ce that does work: PE + KE = constant Energy is conserved Free fall (reminder) V0 = 0 t = 0s V1 = 10m/s t = 1s V2 = 20m/s t = 2s V3 = 30m/s t = 3s V4 = 40m/s t = 4s 75m 60m 35m 0m height 80m

m=1kg free falls from 80m V0 = 0 h0=80m t = 0s V1 = 10m/s; h1=75m t = 1s V2 = 20m/s; h2=60m 600J 200J 800J t = 2s V3 = 30m/s; h3=35m 350J 450J 800J t = 3s V4 = 40m/s; h4=0 0 800J 800J t = 4s mgh ½ mv2 sum 800J 0 800J 750J 50J 800J pendulum W=mg T Two as long as ces: T in addition to W T is always to the motion (& does no work) Pendulum conserves energy hmax E=mghmax E=mghmax E=1/2 m(vmax)2

Roller coaster Work done by a spring Relaxed Position F=0 F x I compress the spring (I do + work; spring does -work) Work done by spring = – change in ½ kx2 Spring Potential Energy Workspring = -change in ½ kx2 This is the: Springs Potential Energy (or PEspring) Workspring = -change in PEspring change in PEspring = -Workspring

If spring is the only as long as ce doing work . -change in ½ kx2 = change in ½ mv2 0 = change in ½ kx2 + change in ½ mv2 change in ( ½ kx2 + ½ mv2) = 0 ½ kx2 + ½ mv2 = constant Work-energy theorem: Conservation of energy springs & gravity mgh + ½ kx2 + ½ mv2 = constant Gravitational potential energy Kinetic energy If elastic as long as ce & gravity are the only as long as ce doing work: PEgrav + PEspring + KE = constant Energy is conserved spring potential energy example KineticE Spring PE grav PE

Two types of as long as ces: Conservative as long as ces as long as ces that do + & work Gravity Elastic (springs, etc) Electrical as long as ces Dissipative as long as ces as long as ces that only do work Friction Viscosity . -work change in PE -work heat (no potential energy.) (-)Work done by frictionheat Thermal atomic motion Heat energy= KE in addition to PE associated with the r in addition to om thermal motion of atoms Air solid

Work-energy theorem (all as long as ces) Workfric = change in (PE+KE) Work done dissipative Forces (always -) Kinetic energy -Workfric = change in heat energy potential energy From all Conservative as long as ces -change in Heat Energy = change in (PE+KE) Workfric = -change in heat energy Work Energy Theorem (all as long as ces) 0 = change in Heat Energy + change in (PE+KE) 0 = change in (Heat Energy+PE+KE) Heat Energy + PE + KE = constant Law of Conservation of Energy Energy conversion while skiing Friction: energy gets converted to heat Potential energy Potential energykinetic energy

Units again Heat units: 1 calorie = heat energy required to raise the temp of 1 gram of H2O by 1o C 1 calorie= 4.18 Joules Kg m2/s2 Food Calories 1 Calorie = 1000 calories = 1Kcalorie 1 Calorie= 4.18×103 Joules The Calories you read on food labels 8 x 105 J 7 x 106 J 2 x 106 J Power Rate of using energy: amout of energy elapsed time Units: Joule second 1 = 1 Watt Power = A 100 W light bulb consumes 100 J of electrical energy each second to produce light

Other units Over a full day, a work-horse can have an average work output of more than 750 Joules each second 1 Horsepower = 750 Watts Kilowatt hours energy time Power = energy = power x time power unit x time unit = energy unit Elec companies use: Kilowatts (103 W) hours (3600 s) 1 kilowatt-hour = 1kW-hr = 103 W x 3.6×103 s = 3.6×106 Ws J HECO charges us about 15 cents /kW-hr x

## Wolfson, Kate Executive Producer

Wolfson, Kate is from United States and they belong to On The House Syndication and they are from Pittsburg, United States got related to this Particular Journal. and Wolfson, Kate deal with the subjects like Home Improvements and Remodeling

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