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# Chapter 3.3 Why Air Bags?

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### Chapter 3.3 Why Air Bags?

1. 1. Good  Morning!   s Today  we  will:   s  complete  Investigation  3.3   s  watch  a  video   s Please  do  before  the  tardy  bell:   s  get  out  your  lab  notebook  &  something  to   write  with   s  have  at  least  one  textbook  on  your  desk   s  be  sitting  at  a  table  with  at  least  one  other   person  but  no  more  than  two  other  people
2. 2. What  Do  You  See?
3. 3. Investigation  3.3   s Turn  to  the  ﬁrst  new  page  in  your   lab  book  and  title  this  lab,  “Why  Air   Bags?”  Be  sure  to  make  an  entry  in   your  Table  of  Contents  as  well.
4. 4. Air  Bags   s How  does  an  air  bag  protect  you   during  an  accident?   s Copy  this  question  down  in  your   lab  notebook  and  take  5  minutes   to  jot  down  your  ideas.
5. 5. Air  Bags   s  How  does  an  air  bag  protect  you  during   an  accident?     s  Now  take  three  minutes  and  share  your   ideas  with  your  table  partner   s  If  you  sit  on  an  odd  number  row,  turn   around  and  share  your  ideas  with  the   table  behind  you.
6. 6. Investigation  3.3   s Read  #  1  –  4  in  the  investigation.   s Be  looking  for  three  things:   s  materials  you  will  need   s  independent  variable   s  dependent  variable   s In  your  lab  notebook,  record:   s  the  materials  needed   s  the  ind  v   s  the  dep  v
7. 7. Investigation  3.3   s Now,  read  #  5  –  7   s Be  looking  for:   s  what  you  will  be  doing  diﬀerently  in   this  part  of  the  lab   s  how  you  will  make  measurements   s Go  back  to  your  materials  list  and   add  the  necessary  new  materials
8. 8. Investigation  3.3   s Create  two  data  tables  –  one  for   each  type  of  drop.  Be  sure  to  fully   label  the  tables:   s  columns   s  rows   s  title   s  units
9. 9. Energy  and  Work   s Look  over  your  lab  data  and  the   original  question  of  the  lab,  “How   does  an  air  bag  protect  you  in  an   accident?”   s After  completing  the  lab,  is  there   anything  you  can  add  to  your   original  ideas?
10. 10. Good  Afternoon!   s  Today  we  will:   s  discuss  how  air  bags  work   s  take  some  notes   s  solve  energy  &  work  problems   s  answer  the  question,  “How  do  air  bags   decreases  the  severity  of  damage  in  a  car   crash?”   s  Please  do  before  the  tardy  bell:   1.  pick  up  a  whiteboard  and  a  dry  erase  marker   2.  get  out  your  spiral  and  something  to  write   with   3.  get  a  textbook  (your  own,  not  shared)
11. 11. Warm-­‐Up  Part  1   s In  today’s  lesson,  we  are  going  to  be   talking  about  two  physics  concepts   we  talked  about  before  winter  break:   s  kinetic  energy   s  work   s You  have  three  minutes  to  ﬁnd  and   write  down  in  your  notes  the   deﬁnitions  and  formulas  for  each
12. 12. Warm-­‐Up  Part  2   Drop     Drop  A  Damage   Drop  B  Damage   Height   2  cm   none   none   4  cm   small  1  cm  crack   none   6  cm   2  cm  long  cracks  along   none   bottom   8  cm    3cm  cracks  and  leakage   none   10  cm   -­‐-­‐-­‐   small  1  cm  crack   12  cm   -­‐-­‐-­‐-­‐   2  cm  long  cracks  along   bottom   14  cm   -­‐-­‐-­‐-­‐    3cm  cracks  and  leakage
13. 13. Eﬀect  of  Drop  Height  on  Egg  Damage   3   2   size  of  cracks  (cm)   1   4   8   12   16   drop  height  (cm)
14. 14. Objectives/Goals   s  By  the  end  of  the  day,  you  will:   s  1.  Relate  kinetic  energy  to  the  work   required  to  stop  an  object.   s  2.  Understand  the  relationship  between   the  force  of  an  impact  and  the  stopping   distance.   s  3.  Write  a  conclusion  that  uses  scientiﬁc   language  to  answer  the  question,  “How   does  cushioning  decrease  the  severity  of   the  damage  in  a  car  crash?”
15. 15. Kinetic  Energy   s Before  winter  break,  we  learned   about  kinetic  energy.   s Review:  What  is  kinetic  energy?   s  the  energy  of  a  moving  object   s  KE  =  0.5  mv2
16. 16. Kinetic  Energy  Review   s Objects  in  motion  have  kinetic  energy.   s KE  =  ½  mv2   s If  mass  is  increased,  what  happens  to   KE?   s  it  increases   s If  velocity  is  increased,  what  happens   to  KE?   s  it  increases
17. 17. Kinetic  Energy  &  the  Egg  Drop   s True  or  False:   s  The  egg  that  dropped  on  the  hard   surface  broke  sooner  because  it  had   more  kinetic  energy.
18. 18. Which  Egg  had  the  greater  KE?   s The  eggs  had  approximately  the  same   mass.   s Both  eggs  were  dropped  from  the  same   height.   s What  do  we  know  about  the  velocity   they  hit  their  respective  surfaces  with?   s  because  gravity  acts  on  all  objects  equally,   the  two  eggs  had  the  same  velocity  when   they  struck  their  respective  surfaces
19. 19. Revisit:  Kinetic  Energy  &  the  Egg   Drop   s True  or  False:   s  The  egg  that  dropped  on  the  hard   surface  broke  sooner  because  it  had   more  kinetic  energy.   s  False  –  the  eggs  have  the  same  kinetic   energy,  so  kinetic  energy  cannot  be  the   reason  one  broke  and  the  other  did  not
20. 20. Which  Egg  had  the  greater  KE?   s The  eggs  had  the  same  kinetic   energy  (when  dropped  from  the   same  height)   s So  why  did  one  egg  break  and  the   other  didn’t?
21. 21. Work  &  Kinetic  Energy   s read  pg  279  –  281   s Focus  Questions:   s  What  must  be  done  to  change  the   kinetic  energy  of  an  object?   s  What  is  a  safe  way  to  “get  rid  of”  the   kinetic  energy  of  a  car?   s  What  is  an  unsafe  way  to  “get  rid  of”   the  kinetic  energy  of  a  car?   s 7  minutes
22. 22. The  Physics  of  Cushioning   s In  order  to  stop  an  object  with  kinetic   energy,  work  is  done.   s Do  you  remember  the  formula  for   work?   s  Work  =  force  x  distance   s The  work  done  to  bring  an  object  to  a   stop  is  exactly  equal  to  the  amount  of   kinetic  energy  the  object  has
23. 23. The  Physics  of  Cushioning   s Work  can  also  increase  the  kinetic   energy  an  object  has.   s Whether  work  increases  or   decreases  kinetic  energy  depends   on  the  direction  the  work  is   applied  from  and  the  direction  of   the  object  that  is  moving.
24. 24. The  Physics  of  Cushioning   s Bottom  Line:   s  the  amount  of  work  done  on  a   moving  object  is  equal  to  the  object’s   change  in  kinetic  energy   s We  represent  this  relationship  with   a  formula:   s W  =  ΔKE
25. 25. Check  Yourself   s A  rolling  bowling  ball  has  1000   joules  of  kinetic  energy.  After  a     certain  amount  of  work  is  done  to   the  bowling  ball,  it  has  300  J  of   kinetic  energy.   s  How  much  work  was  done?   s  700  J
26. 26. Check  Yourself   s  Our  ﬁrst  objective  today  was:   s  relate  the  energy  of  a  moving  object  to  the  amount  of   work  needed  to  stop  the  object.   s  Explain  to  your  table  partner  how  work  done  on   an  object  and  the  object’s  kinetic  energy  are   related.   s  Take  ﬁve  minutes  to  write  down  your  ideas  about   the  relationship  in  your  notes.  Be  sure  to  give  a   title!
27. 27. Bringing  an  Object  to  a  Stop   s How  much  work  is  needed  to  stop  an   object  with  3000  joules  of  kinetic   energy?   s  3000  joules  (newton-­‐meters)  of  work   s How  much  work  is  needed  to  stop  an   object  with  1500  joules  of  kinetic   energy?   s  1500  joules  (newton-­‐meters)  of  work
28. 28. Bringing  an  Object  to  a  Stop   s How  much  work  is  done  to  stop  an   object  with  500  joules  of  kinetic   energy?   s If  you  apply  100  N  of  force  to  stop   this  object,  how  far  will  it  travel   before  it  stops?   s  Hint:  remember  the  formula  for  work
29. 29. Mathematical  relationship  between   work  and  kinetic  energy   kinetic  energy   force     distance   work  done   500  J   100  N   5  m   500  J   500  J   250  N   2  m   500  J   500  J   500  N   1  m   500  J
30. 30. Mathematical  relationship  between   work  and  kinetic  energy   Draw  this  table  in  your  notes  and  ﬁll  in  the  blanks   kinetic  energy   force     distance   work  done   1000  J   100  N   _____  m   _____  J   _____  J   _____  N   2  m   1000  J   _____    J   250  N   4  m   _____    J
31. 31. Mathematical  relationship  between   work  and  kinetic  energy   Draw  this  table  in  your  notes  and  ﬁll  in  the  blanks   kinetic  energy   force     distance   work  done   1000  J   100  N   10  m   1000  J   1000  J   500  N   2  m   1000  J   1000  J   250  N   4  m   1000  J
32. 32. Check  Yourself   s Look  back  in  you  notes  where  you   jotted  down  your  ideas  about  how   work  and  kinetic  energy  are   related.   s Now  add  speciﬁc  mathematical   example  to  your  list?  (Do  your  own   math,  don’t  just  copy  from  the   table!)
33. 33. The  Physics  of  Cushioning   s If  you  look  back  on  the  table  you   just  created,  you’ll  see  that  as  long   as  kinetic  energy  remains  constant,   the  smaller  the  stopping  distance,   the  larger  the  force.   s We  saw  this  in  the  egg  drop  lab:   the  stopping  distance  in  the  ﬂour   was  the  indentation  in  the  ﬂour.
34. 34. The  Physics  of  Cushioning   s re-­‐read  pg  281  in  your  textbook   s  focus  on  what  an  air  bag  does  in  a   crash   s  3  minutes
35. 35. The  Physics  of  Cushioning   s An  air  bag  works  by  increasing  the   stopping  distance  of  your  face  and   chest  in  a  car  crash.     s Increased  stopping  distance  means   there  will  be  a  decreased  force.  When   we  are  talking  about  your  face  and   chest,  this  is  a  good  thing.  J
36. 36. Objectives/Goals   s  Our  second  objective  today  was:   s  demonstrate  an  understanding  about  the   relationship  between  the  force  of  an  impact   and  stopping  distance   s  If  the  kinetic  energy  of  two  cars  is  the   same,  and  Car  A  has  1000  N  of  force   applied  and  Car  B  has  3000  N  of  force   applied,  which  car  stops  in  a  shorter   distance?   s  Car  B  –  because  it  has  a  greater  force  applied
37. 37. Time  to  Throw  an  Egg!
38. 38. Relationship  between  kinetic  energy,   force  of  impact  and  stopping  distance   s True  or  False   s If  stopping  distance  is  held  constant   and  kinetic  energy  is  increased,  the   force  of  the  impact  will  increase.   s  True  –  since  the  change  in  kinetic  energy   is  equal  to  the  work  done  (w  =  fd)  and   distance  is  held  constant,  increasing  the   work  done  (because  kinetic  energy  was   increased)  means  force  will  increase  as   well.
39. 39. Relationship  between  force  of  an  impact   and  stopping  distance   s Copy  down  these  sentences  and  ﬁnish   them  in  your  notes:   s If  kinetic  energy  is  held  constant,  the   greater  the  stopping  distance…(what   happens  to  force  of  impact?)   s If  kinetic  energy  is  held  constant,  the   force  of  an  impact  increases  when… (what  happens  to  stopping  distance?)
40. 40. Relationship  between  force  of  an  impact   and  stopping  distance   s Copy  down  these  sentences  and  ﬁnish   them  in  your  notes:   s If  kinetic  energy  is  held  constant,  the   greater  the  stopping  distance…the   less  the  force  of  impact.   s If  kinetic  energy  is  held  constant,  the   force  of  an  impact  increases  when… the  stopping  distance  is  decreased.
41. 41. Final  Check  Yourself   s The  main  objective  of  this  lesson:   s  Write  a  conclusion  that  uses  scientiﬁc   language  to  answer  the  question,   “How  does  cushioning  decrease  the   severity  of  the  damage  in  a  car   crash?”
42. 42. How  does  cushioning  decrease  the   severity  of  the  damage  of  a  car  crash?     s On  a  clean,  whole  sheet  of  paper,   copy  down  this  question  and     answer  it  fully  using  scientiﬁcally   accurate  language.   s  you  may  ﬁnd  it  helpful  to  create  a   concept  map  or  organize  your   thoughts  with  a  graphic  organizer
43. 43. How  does  cushioning  decrease  the   severity  of  the  damage  of  a  car  crash?     s Proﬁcient  answers  will  include:   s  evidence  that  you  can  relate  the   energy  of  a  moving  object  to  the   work  needed  to  stop  the  object   s  evidence  that  you  understand  the   relationship  between  the  force  of  an   impact  and  the  stopping  distance   s  scientiﬁc  language