How Things Work
How Things Work PHYS 1000
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This 4 page Class Notes was uploaded by Zula Tromp on Wednesday September 30, 2015. The Class Notes belongs to PHYS 1000 at Western Michigan University taught by John Tanis in Fall. Since its upload, it has received 22 views. For similar materials see /class/216931/phys-1000-western-michigan-university in Physics 2 at Western Michigan University.
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Date Created: 09/30/15
PHYS 1000 Spring 2009 How Things Work 3rd ed Louis A Bloom eld CHAPTER REVIEWS THE LAWS OF MOTION Part I inertia mass the property of objects that resists changes in motion speed distancetime velocity involves speed and direction NEWTON S FIRST LAW objects at rest remain at rest objects in motion remain in motion in a straight lineunless acted on by outside in uences forces acce1eration how fast velocity changes with time speed g direction may change NEWTON S SECOND LAW to make something accelerate requires a force a push or pull force mass X acceleration F ma falling objects a11 objects fall at the same rate without air resistance g 98 mss velocity acceleration X time v at distance 12 accel X time2 d 12 atz proj ectile motion horizontal motion and vertical motions are independent weight m of gravity weight mass Xacce1 of gravity mass X 98 mss NEWTON S THIRD LAW for every action there is an equal and opposite reaction net force the m of all forces acting on an object determines its motion potential energy PE stored energy kinetic energy KE energy of motion ENERGY IS CONSERVED work transfers energy work force X distance moved THE LAWS OF MOTION Part II rotationa1 inertia resists changes in rotational motion rotational speed how fast something rotates revolutions per second for eXample NEWTON S FIRST LAW OF ROTATION objects not rotating don t start rotating objects rotating continue to rotate unless acted on by an outside in uence torque torque required to make something rotate torque force X lever arm centerofmass quotaveragequot center of an object a freely spinning object rotates about its centerofmass NEWTON S SECOND LAW OF ROTATION torque rotational inertia X rotational accel friction always opposes motion depends on surfaces weight relative motion static surfaces at rest sliding surfaces move relative to each other sliding friction is smaller than static friction friction transforms kinetic energy into thermal energy energy conserved momer1tum mass and velocity determine how hard it is to start or stop something momer1tum mass X velocity re1ationship to force and time force X time change in momentum Ft change in mom in collisions MOMENTUM IS CONSERVED spinning objects ROTATIONAL MOMENTUM IS CONSERVED NEWTON S THIRD LAW OF ROTATION for every torque there is an equal and opposite tor ue kinetic energy increases as velocity squared KE 12 mvz Chap 6 MECHANICAL OBJECTS PartI springs force required to stretch or compress a spring is proportional to how much it is stretched or compressed true for nearly anything that is stretched or compressed spring constant spring forcestretch elastic potential energy PE energy stored in a spring that can be converted to KE bouncing balls eXperience a quotspringquot force when they strike something gravitational PE gt KE collision energy gt elastic PE thermal energy elastic PE gt KE rebound energy gt gravitational PE so final height lt initial height coe icient of restitution outgoing speedincoming speed naliheightinitialihei ght balls bouncing from moving surfaces eg a bat or a tennis racket 7 allows increase in return speed quotsweet spotsquot for bats tennis racquets etc center of percussion bat or racquet rotates about end of handle when struck at this point vibrational node no vibration when struck at this point circular motion an hing moving in a circle experiences a centripetal acceleration and consequently a centripetal force magnitude of centripetal acceleration accel speed2radius centrifugal force outward force is a quot ctitiousquot force 7 reaction to inward force applicable to roller coasters looptheloops etc FLUIDS liquids and gases 7 Sec 51 pressure force area air pressure due to weight of air above us about 15 lbsin2 100000 Pascals pressure depends on altitude in air or depth in a liquid density massvolume Ideal Gas Law press gtlt volume density gtlt temperature buoyancy reduction in weight when an object is immersed in a uid Archimedes39 principle buoyant force weight of displaced uid applicable to helium balloons hotair balloons oating objects FLUIDS AND MOTION 7 Sec 62 Bemoulli39s principle pressure in a uid corresponds to potential energy PE velocity of uid corresponds to kinetic energy KE loosely stated pressure decreases with increased velocity or KEvelocity of uid PEpressure of uid constant energy this is conservation of energy laminar air ow smooth orderly ow of air turbulent air ow rough random motion of air 0 Chap 1 Chap 11 RESONANCE AND MECHANICAL WAVES 7 Secs 91 and 92 natural frequencies the frequencies at which an object oscillates when struck resonance occurs when an object is made to oscillate at its natural frequenc clocks characterized by period T of oscillation 7 time for one complete oscillation period lfrequency pendulum period depends only on length mass on a spring balance clocks period depends only mass or rotational inertia electronic quartz crystals designed to oscillate at 32768 Hz period of all clocks is independent of the amplitude of oscillation sound and music sound results from oscillations of air molecules like a Slinky human hearing 20 Hz 7 20000 Hz 1 Hz l cyclesecond octave sounds that differ by a factor of 2 in frequency pitch violins and guitars frequency pitch depends on mass length tension of strings vibrates in fundamental frequency and higher harmonics at the same time bowing and plucking audible sound comes from coupling the strings to the soundboX organ pipes sound comes from oscillations of air inside the pipe frequency determined by length of air column drums sound results from oscillations of a twodimensional surface compared to one dimensional oscillating strings and air columns ELECTRICITY 7 Secs 10land 103 Electricity and the Flashlight s Electric Circuit electric charges positive and negative protons and electrons like charges repel unlike charges attract charge is conserve charge is quantized always some multiple of the charge on an electron obj ects become charged by transferring electrons usually three categories of materials conductors insulators semiconductors electric force increases with charge and decreases with separation between charges voltage measures electrical PE similar to gravity or a spring electric circuits example a ashlight closed circuit continuous path for charges electrons to ow from a battery open circuit no continuous path for charges to ow switch open short circuit occurs when wire is connected directly across a battery MAGNETISM AND ELECTRODYNAMICS magnetic poles north and south like poles repel unlike poles attract magnetic poles always occur in pairs magnetic materials soft easily magnetized hard difficult to magnetize ONNP TIONS BETWEEN EI ECTRICITY AND MAGNETISM moving electric charges produce magnetism changing magnetism moving magnetic poles produces electricity transformers used to increase or decrease AC voltages principle of operation changing current in primary coil 3 changing magnetic eld 3 changing current in secondary coil with higher or lower voltage applications of changing electric and magnetic fields loudspeakers and microphones opposites of one another airport security triggering of traffic signals Chap 13 ELECTROMAGNETIC WAVES EM electromagnetic waves produced by making charges run up and down an antenna consist of electric and magnetic parts that are perpendicular to each other Fig 13 14 electric and magnetic parts continuously regenerate each other in empty space travel at the speed of light light is an EM wave 186000 milessecond reception of EM waves 1 conducting rod 7 responds to electric part of wave causes charges to oscillate 2 conducting loop 7 responds to magnetic part of wave induces current audible information 20 720000 Hz carried by modulation variation of carrier wave AM amplitude modulation 550 7 1600 kHz kilohertz FM frequency modulation 88 7 108 MHZ megahertz TV video carried by AM audio by FM cell phones transmit and receive EM waves microwave ovens EM waves produced by a magnetron directed into cooking chamber by a waveguide HZO molecules forced to twist rotate by EM waves of 245 GHZ gigahertZ collisions friction between HZO molecules cause them and food to get hot Chap 12 ELECTRONICS 7 Sec 122 pp 404406 digital representation of sound waves Chap 15 OPTICS 7 Sec 15 2 pp 489494 digital recording sound wave is sampled at regular time intervals 44100 timessecond for a CD up to 96000 times per second for a DVD amplitude air pressure of wave is assigned a number between 32768 and 732768 216 bits information stored on a re ective layer gold aluminum as pits and land at areas information read by bouncing laser light from the re ective layer Fig 1522 optical system focuses laser light and determines amount of re ected light Fig 1523
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