1Physics 1010:The Physics of Everyday LifeTODAY• Review Work, Concervation of Energy• Fluids2Admin stuff• Exams are at back of room, in fouralphabetical piles. Please take AFTER class• Some clicker numbers still without owners.• Some students still without clicker numbers.• If you’re in either category talk to Yu (thesooner the better).• Letter grades: you can drop all of thegrades so far (and so can everybody else) soletter grades rather pointless at this stage• Makeups: NONE (you can drop grades)3• Kinetic Energy: the energy in a moving mass;Ek=(1/2)mv2• Potential Energy: the energy stored in a masspushed up against a force (gravity, mgh; spring,(1/2)kx2)• Heat: The energy stored in a mass by virtue ofits temperature (kinetic) Through work we can convert any one to anyother!Different Kinds of Energy4A note about friction• Friction force varies with lots of things …roughness of material, little things sticking upon surface, etc.• But we can find an average friction force for aparticular type of surface. Many fairly smoothsurfaces near friction force of 0.3 x weight(this is called the coefficient of friction, µ).5Push weight (file cabinet, stone block) across board.Weight of “file cabinet” = 19.5 N, µ =0.3 Ffriction = 0.3 x weight = 5.8 NSlide it 0.5 m. Work done (Force x distance) = ? a. 5.8 J, b. 19.5 J, C. 2.9 J., d. 11.6 Janswer: C. = 5.8 N X 0.5 m = 2.9 J0. 5 m6.25 m0. 5 mNow push it (weight = 19.5 N) up a hill so it goes up 0.25 m inmoving 0.5 m. How much work will it take to push it up (µ=0.3)?a. 2.9 J. b. 4.9 J, c. 9.8 J, d. 19.5 J, e. 7.8 Jans. is e: 7.8 J. Total work = work against friction (= 2.9 J) + work to lift it up against gravity (= mg*change in height = 19.5 N x 0.25 m = 4.9 J = 7.8 JSo now, how muchforce is required topush it up the board?a. 9.75 N, b. 15.6 N, c. 19.5 N, d. 5.8 N, e. impossible to tellans. is b: 15.6 N. work=force x distance = 7.8 J from above = F x 0.5 m.so F= 7.8 J/0.5 m = 15.6 N.7How much of food goes into work?How much force x distance can person do?easy to measure with stationary bicycle. elite women bicyclist can produce 300 W power, typical tour de France rider 400 W of power, [~1/2 horsepower]and Lance Armstrong can hit 500 W of power. Athletic man sustain ~150 watts (nonheat!) for 10 hour day= 150 J/s x 10 x 60 x 60 s = 5,400,000 J of work/day.How many calories is this?a. 2140 cal, b. 1290 cal, c. 150 cal d. 12000 cal b. 5.4E6 J/4184J/cal =1291 cal.eats ~ 5800 cal/day1 food calorie = 4184 J. where does the rest of the energy (5800-1291=4500 cal) go?a. chemical, b. sweating, c. light, d. heat, e. odord. heat.(80%)8Group project (will be posted on website):How much food did Egypt have to growto build the great pyramid of Cheops• A How many days they worked on it• B how many blocks you have• C how many raws of blocks you have• D how many people worked on it• E the mass of each block• F total hight• G How many days each worker workedNeed to know:9Group project (will be posted on website):How much food did Egypt have to growto build the great pyramid of Cheops• H how many calories per pound of grain• I the coefficient of friction• J what color were their shoes• KNeed to know:10Today’s topics• Air and air pressure• Pressure, density, and temperature• Archimedes principle & buoyant force• Ideal gas law• Hot air balloons• Helium balloons11Gases• Consist of molecules (about 10-9 m across) thatbounce around• They do not fall to ground because they havekinetic energy [(1/2)mv2 ]• More kinetic energy means more temperature• Bouncing off the wall causes it to exert a force(concervation of momentum; Newton’s III)12Pressure: bouncing off the wallsThe piston is free tomove. After the tinymolecule hits it, thepistona) shakesb) moves to the left atconstant velocityc) accelerates to the leftd) remains stationaryThe piston moves to the left atconstant velocity, as it acquiredmomentum from the molecule(concervation of momentum).13Pressure: bouncing off the wallsThe piston is free to move.Molecule after moleculehits it, the pistona) shakesb) moves to the left atconstant velocityc) accelerates to the leftd) remains stationaryThe piston accelerates to the left aseach molecule gives it moremomentum, meaning…..THERE IS A NET FORCE ON THE PISTON14Pressure: the force per unit area• More area exposed to gas implies more collisions• More collisions implies more momentum transfer• More momentum transfer implies more force• Force = Pressure x Area• Pressure = Force/Area• Unit: 1 Pascal (Pa) = 1 N/m2• Atmospheric pressure = 100,000 Pa = 105 Pa =14.7 lbs/sq. inch15Pressure is in all directions• Water comes outwhether cork is ontop, side, or