Pu answers in boxes
Main Ideas in Class Toda Inroducion o Falling Appl Old Equaions Graphing Free Fall Sole Free Fall Problems Pracice:.45,.47,.53,.59,.61,.63,.69, Muliple Choice.1
Freel Falling Objecs Refers o objecs which are no held, bu are free o fall near he Earh s surface (oher cases Ch. 7) All objecs fall wih he same consan acceleraion due o grai in he absence of air resisance!
No Air on he Moon When Asronau Daid Sco dropped a feaher and a hammer on he moon, which hi he ground firs?
+ Acceleraion Due o Grai We can ofen ignore air resisance, which picall has a small effec (excepions: feahers, parachues, big surface area/weigh). Acceleraion due o grai poins owards he ground (owards he cener of Earh) Magniude is g = 9.8 m/s near he surface of Earh In free fall, a = ± g depending he direcion is defined (I like o alwas define + as up) x o =100 m Wha does ha mean abou he sign of acceleraion, eloci and displacemen? Thus, in his figure, a, eloci and x are all negaie (wha happens if I flip +)! x f =0 m x = x f x o = 0 m 100 m = -100m
These are he onl formulas ou need for Used: To Ge: Tes 1 and he will be gien! besides rig a f f i i o a x o 1 a o ax In free fall, he onl acceleraion is due o grai: a=g (consan) We also generall use insead of x (because erical moion) x f f x i i Deried in book, bu ou don need o know how o derie hese formulas o Aerage of numbers + Define down o use a=+g Define up o use a= -g + o g o 1 g o g Same formulas jus differen leers A lo of confusion abou phsics is jus due o calling he same hing b differen leers
Similar o Homework A baseball is hrown up in he air a an iniial eloci of.0 m/s. (a) How high up does i go? (b) How long is i in he air if ou cach i a he same heigh ou iniiall le go of he ball? a o x o 1 a o ax
Same sle as some concepual quesions on he es If ou oss a ball upward wih a cerain iniial speed, i falls freel and reaches a maximum heigh h. B wha facor mus ou increase he iniial speed of he ball for i o reach a maximum heigh 4h? A. B. 3 C. 4 a o x o 1 a o ax Jus because i s a concepual problem, doesn mean ou can use numbers. D. 8 E. 16 Q11
No Talking This Time! A ball is ossed sraigh up ino he air. Which of he following represens he signs ( ) of he acceleraion as i moes upward, reaches is highes poin, and falls back down? Moing upward Highes poin Falling back down A. + 0 - B. - 0 - C. - - - D. None of hese Q1
(displacemen) ( eloci) + Graphing Freel Falling Bodies a = -g = -9.8 m/s Equaion of a sraigh line mx b ground x m is slope, b is -inercep 10 o o 1 g o g -5-10 -15 10 5 5 0 0.0 0.5 1.0 1.5.0.5 3.0 0 0.0 0.5 1.0 1.5.0.5 3.0-5 -10-15 -0-0 -5
You Ma Talk This Time A ball is ossed sraigh up ino he air. Which of he following represens he signs ( ) of he acceleraion as i moes upward, reaches is highes poin, and falls back down? Moing upward Highes poin Falling back down A. + 0 - B. - 0 - C. - - - D. None of hese Q1
+ Acceleraion Due o Grai Acceleraion due o grai poins owards he ground (owards he cener of Earh) Magniude is g = 9.8 m/s near he surface of Earh In free fall, a = ± g depending he direcion is defined NOT ON WHICH DIRECTION YOU ARE GOING! x o =100 m x f =0 m
Common misconcepion ha a=0 a op of pah 10 5 o o 1 g 0 0.0 0.5 1.0 1.5.0.5 3.0-5 -10-15 -0 10 5 a 9.8 m/s 10 5 o g 0 0.0 0.5 1.0 1.5.0.5 3.0-5 -10-15 -0-5 Noe: is a maximum a he same insan when = 0 a (m/s ) -10-15 0 0.0 0.5 1.0 1.5.0.5 3.0-5 Noe: a = -9.8 m/s alwas, een a op of he rajecor!
If ou drop an objec in he absence of air resisance, i acceleraes downward a 9.8 m/s. If insead ou hrow i downward, is downward acceleraion afer release is A. less han 9.8 m/s. B. 9.8 m/s. C. more han 9.8 m/s. Q13
A small bag is released from a helicoper ha is descending seadil a 1.50 m/s. (a) Afer 4.00 s, wha is he speed of he bag? (b) A 4 s, how far is i below where i was when i was dropped? (c) Wha are our answers o pars (a) and (b) if he helicoper is rising seadil a 1.50 m/s? Noice ha a change of he sign of eloci affecs he answer!
Concepual Problem A person sanding a he edge of a cliff hrows one ball sraigh up and anoher ball sraigh down a he same iniial speed. Neglecing air resisance, he ball o hi he ground below he cliff wih he greaer speed is he one iniiall hrown a o A. upward. B. downward. o ax C. neiher he boh hi a he same speed. x o 1 a Jus because i s a concepual problem, doesn mean ou can use a formula o help ou hink abou i. Q14
Figuring Ou Which Formula (main formulas gien on exam) x f f x i i x x x o o 1 a o ax o Eq. A Eq. B Eq. C Eq. D a Lis our knowns and unknowns: consan eloci x, o,, a o,, a, Someimes easier o find which formula does no hae he ariable ou are NOT considering Same sraeg applies o mulipar quesions, ou jus do one par a a ime. Someimes need answer from a o answer b
Injur from Falling and/or a Collision I s no he falling ha hurs, bu he sopping Skdiing a a=9.8 m/s is fine When we sop, a is much more han 9.8 m/s How do rea a problem wih acceleraions?
Concussions: The Grai of I All Pun inended Traumaic brain injur resuls when he head undergoes a er large acceleraion. hp://www.ncbi.nlm.nih.go/pmc/aricles/pmc155415/ Generall, an acceleraion less han 800 m/s lasing for an lengh of ime will no cause injur, whereas an acceleraion greaer han 1000 m/s lasing for a leas 0.001 seconds will cause injur. So wha do we need o know in order o ge ime and acceleraion?
Challenging Applicaion: Child Falling from Bed Suppose a child rolls off a bed ha is 1.0 m aboe he floor. If he floor is hardwood, he child's head is brough o res in ~.0 mm (carpe ~ 1.0 cm, 5x more). Calculae he magniude (and duraion) of he acceleraion for hardwood o deermine he risk of injur. Wh is his a challenging problem?
Clicker Answers Chaper/Secion: Clicker #=Answer Ch.A: 1=E, =E, 3=D Ch.B: 4=B, 5=C, 6=E, 7=C, 8=A, 9=E, 10=A Ch.C: 11=A, 1=C, 13=B, 14=C