Week 3 - PHYS 1750 Notes
Week 3 - PHYS 1750 Notes PHYS1750
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This 7 page Class Notes was uploaded by Emily Notetaker on Friday September 11, 2015. The Class Notes belongs to PHYS1750 at University of Toledo taught by Anderson,L in Fall 2015. Since its upload, it has received 31 views. For similar materials see Introduction to Physics in Natural Sciences and Mathematics at University of Toledo.
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Date Created: 09/11/15
PHYS WED Force Karin Kyhlmann 2038 Elmnml Force PHYS 1750 Force Force is somewhat of an abstract concept We do not observe force We do observe acceleration and infer a force causing it Contact forces vs figld forces one object accelerates another by direct contact Examples sports activities cars pulling pushing one object accelerates another at a distance Examples gravity electric and magnetic fortes 1 Contact forces are caused bv microscopic electric fields between atoms that act like tiny springs resisting compression or expansion 2 Field forces are caused by the exchange of forcecarrier particles Which transfer momentum from one elementary particle to another PHYS l 7 50 Force An object at rest will stay at rest and an object in motion will stay 39 moving at constant speed on a straight path unless acted upon by a momma0 W as 9 l VS 1 SM l net external force is that which resists force acceleration An object accexlerates in the direction of the force applied with a39 value given trythe force divided h39v the mass or The first form is the cause effect the second de nes force F Note looth o and F are directional expressed in boldface font a Units the units of mass are lrg the units of are m force of gravity on something g 98 rnlls2 down In physics has units al In European markets has units of kg N I m In physics For every force there is an Equal and opposite reaction force acting on a drffier ent object PHYS 1750 Force An aside on the equivalence of inertial and gravitational mass Newton s 2lid law defines force in terms of mass and acceleration Newton s law of gravitation states the gravitational attraction force of one mass on another Where is the and d is the distance between the centers of the two masses Are theyquot the same The answer is yes as far as we know if the above two equations were all there was to it then we could adjust the value of G to insure equivalence However Einstein39s general theorv of relativity provides an independent confirmation PHYS WED Force Examples of simple force problems What force is required to support a 126 kg book against gravitv on Earth r me so it 125 x 930 123 IN N A block with mass M is connected to a smaller block of mass m with a llv wire The smaller block is pulled by a second wire with force F TenSlOIk l 01 W What is the tension force Tin the wire between the blocks lac JD Assume no friction Both blocks accelerate with d The only force acting on M is the tension T so W ilms A of mass 015 kg drops 23 m to the floor and rebounds 0 l perfectlv it is in contact with the floor for 0012 seconds What is the W H M In 391 average force during the impact I 1 M W Time to fall to floor solve z in gt2 for t 5 969 5 Velocity just before the floor gt 4576 mils after 66 mils o 576 I rEJEHIQEIZ 1130 misl F ma 170 N PHYS WED Force Review questions We never observe force We observe the consequences of force What is the consequence of force acting on an object Be prepared to give examples of or distinguish among a list of contact vsfieid forces Whv is there no real distinction between contact and field forces Be able to list Newton39s three laws of motion What is the Si unit of force in terms of fundamental 5i units What is inertia What is the difference between mass and weight Rita accelerates a 05 kg ball from rest to 8 mfs during the 01015 in which her foot is in contact with the ball What average force does she applv to the ball during the kick 40 N What is the distinction between inertial mass and gravitational mass in tennuthdai micl hbml u nwm PHYS 175E Force Applications Equilibrium and the normal force all forces on an object cancel and there is no acceieration hat which prevents an object frnm accelerating through a surface lalse called compression Always pushes back perpendicular to the su action of atoms resisting penetration is the I r39rringquot m 05 66 Kunmrnl three l39rlcunn N r costa 2 coef cient of frictipn PHYS HEB Force Applications Pulling force on a wire or rape really any force trvlnn tn pull apart Example sliding a be along the fleer N mg lkinlm d u gtow mg Setup l39nr timings pulled wi lh tension T New the manual farce lblue arrow is manned by the vertical compoan eff Trapeze artist of mass m is pulled ever by tension Tl no the M g angle H vertical are the value al T Ti Ans ees my T3 T sinli PHYS l 750 Force Applications Tension is always uniform along the wire and pulls with equal and opposite values en the objects at the ends of the wire Pulling on the rape with a tension just ever MSW will liftthe mass Hm one has tn pull twice as far to lift the mass one meter hwy 39 V against slitImus f is sufficient to prevent slipping insufficient to prevent slipping MOImal mews J Nun R WWCS Ccoc cien sHli MgL mutate do gm swan SMU V quotHuqh skaPic 1 rcch Blm grave BlLAC emua possible Marl ion Slows Win35 down L509 in carp div OF MO rfoIx am on mockchoqs onk maSSwel l lx l docsvu A WW M slip Our smk D2A LY Ne I m sin 04 m c0504 Accel Jam le Fore m Ne nor Force Nol enowaa 0 NH from Procr mg I COSOQ Tl TI LV Q CDSOlt However one has to pull twice as far to lift the mass one meter PHYS H ED Force Applications Examples CD A sled weighs 10D M It is held in place on a frictlonless 30 slope by a rope attached to a stake at the top the rope is parallel to the slope Find the tension in the rope The downslope component of grauitir is mg sinioi 100 siniBDi 50 N D A 3 5 kg box is sitting on a horizontal floor If the box has a coefficient of kinetic friction of 045 what horizontal tension is required to move it at constant speed across the floor The friction force is in N 04593993 150 N tension if no accel A 32 kg box sitting on a ramp has a coefficient of static friction of 021 lfthe ramp is raised at what angle will the box begin slipping 3 The down slope component of gravity mg sinloi must the Lipslope value of the friction force uN In mg casual Divide both sides by mg cosloi tanioi n so or 120 PHYS 1750 Force Applications Review questions What is the normal force What is friction What is the typical formula for the force applied by sliding friction What is pi in that formula What determines its value Be able to set up and solve slliding friction prolbiems What is tension Be able to set up and solve tension problems How do pullieys provide a llifting advantage ram fgmg 39 Elm l l x 7910 YL J45 u L K F iW x Ingsiniu l1 7 ill T normal Micronquot 39 C ri39i l 9 5 m cusmi 4 MthAm3 45x35xn8 Mmjcosx m3 sinoc SlhOC ILL Cosoc tanx A Frederir E Church 1357 Magma Falls PHYS l 750 Energy Text 71 4 76 Work and energy are common social terms but physics requires measurable quantities Both work and energy are quantities The incremental amount of work done by a force on an object is Where As is a vector displacement along a path Pam F5 is the component of F in the direction of the path Only the part of the farce directed along the path contributes to werk Forces perpendicular to the path do not ths 1 e50 Energy we tam 4 AS AX a What deee week tie It increases the kinetic energy ef the ebjeet 3 0L AX V 1 3 eWF5eeme ee Zeix en e1 v a 2 115 he en a ewe 15 tent 2 a 051 mung mm A3 f L mvg J W Vog 7 2 9 De ne kinetic energylF w T mem J ulE S Euinc c v AH Hne WOVK MS 0M LA 0 a KinePic e e If were enel emetic energy were ell there tweetelemM eemethzlhg weuld he on 36 Vaca mi eelhg eliter ellL we tie werk whee we lift eemethirjtg EEE lWEt Stalinith a but we de net euplv kinetic eenerge re the ehjieet in that ease l f N m3 9 Ineteem 7 a quot nah 31m PHYS l 1 50 Energy Text eate Let eemethihg zef meee m fell e diste nee heeetding te the were kinetic emetgt theerem at the end ef the fell a the WEEK will have quot 7 39 N04 Chgjmlf j cine PIC E mug Ice a m r x at I i going Po f oQ E If we bite the DUJEEI up ene t5 elee delng mgh emleuiht ef werik Peteetiei energy is the were e39ene te Separate ebjeete under ettreetien Ina er squeeze them teg39ether under repeleien 0 a teller eeeetet 39 quot i i were dene he frietiien i e 39 where e le the tetel peth dletertee the ehjieet hes meeed PHYS 17395390 Energy Text Ille i l I I I Springs mereeeleee ebeewi39 39 39 where I is the eeetet diepleeemeht ewey irem equilibrium E O 9 l i F T 7 7 a m V 0W Equll MW X K J FoSlHM welteretheeumeefall m Awe mew 1 and 39 i 39 where the sum is at all the little hits ef the path W H a i H iili area at triangle in the figure ll PHYS i F SU Enereg Test it tie Eaahnple prehlems CD The Millennium Farce reller ceaster at Cedar Paint has an initial drug at 91st In if there was he frictien hnw fast weultl the ceaster cars he musing at the hetten39l at the arch mgH nt 3 15 mt Eelsei h 55 2kg skier skis tilawn a 21 sinpet starting at rest 525 m higher than the base Tlhe caet cient cit frictien is Neglecting air resistance haw fast is he mptring when he reaches the these at the slope Ptentiall at tap a rngH EM at bettern 05 3 mgH pr N s N e rng sea 21quot i e3 2 gH an g ces 21quot H I sin 21 1 s7 h railrciasci car with a mass at 19000 kg is railing at 135 mils tnwarcl a humper at the end at the track censistin at a heainir spring with spring censtant it Win Hinw far deals the spring cempress when the car hits it HES the hefnre L5 is eliter Seine far it Uriel n1 PHYS 1 t Energy Test r let the Ftesiew questinns Hrnw werk de ned in physics When net werlt is dune can an ehiectt what happens lnitquothat is kinetic energy What is the Si unit ef39wnrk and energy In fundamental El units What is the wnrk r kinetic energy theerern and haw is it applie Be able he set up anti seine simple w39nrli e kinetic energy problems What is petential energy Haw much petential energyr is aclclleti he an ehiect if it is raised is m What is Heelser law What are the units fer the spring censtant it Hew much petential energyr is stared in a spring cempresseci s m Hiew is censersatien ef mechanical energy expressed Under what candiitiens is mechanical energy conserved Be able ta set up anci seine simple spring prehiems Tent questiclns T313111 ill 11 12E 122 12 9 chute m bx rm 6 1 v1 a 3M okg EE aaes LIAO39ms1 F mag OIO x l2O 39 IOQM OO log N f ballN