Harry Potter and the Prisoner of Askaban: The Knight Bus

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Harry Potter and the Prisoner of
Askaban: The Knight Bus
Scene Description
●
Harry Potter decides to take a ride on the magical Knight Bus. This bus defies
gravity many times during the scene.
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The braking force of this speed is too great
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The stopping distance of the bus going this velocity would require a much
longer stopping distance
–
The time is still wrong in order to stop within this distance
–
The force to stop in the movie does not match up with the actual force it would
take the bus to stop
–
Harry should fly through the windshield after stopping that instantly
The Scene
The Knight Bus
Physics Concepts
Stopping distance of bus
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●
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Determine velocity of bus using a distance interval and
the travel time of that interval
Determine the bus' momentum with momentum formula
Impulse momentum theorem to determine the braking
force needed to stop the bus
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Braking force to stop bus in the time it stops in movie
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Find actual stopping distance for time in movie
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More Physics Concepts
Force to stop a bus going this speed
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Determine force of friction
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Determine net force (ma)
Prove windshield would break
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Impulse momentum to determine force at which Harry would be
traveling
Compare to force it takes to break a windshield
Estimations
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1 city block~ 100,000 sq.ft.
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1.93s to travel 1 block
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20,360kg estimate for triple decker bus
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Average male mass: 70kg
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About 10 passengers on bus (70kg each)
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100kg for fuel tank
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5m estimated distance bus takes to stop
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1.5s estimate stop time of buss in scene
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.055s estimate time face hits glass for
Calculations
Timing the bus as it travels
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1 city block~ 100,000sq ft
100,000 = 223.62ft
223.62
3  
= 74.54m
Velocity=
V=


74.54
1.93
V= 38.6218

Determining the mass of the bus
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1 double decker bus~ 14,560kg +
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1000kg extra floor +
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70kg per person x 10 people +
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100kg fuel tank and fuel = 20,360kg estimate mass of triple decker
bus
Braking force of the bus in the scene
Impulse Momentum Theorem:
Stopping distance the bus needs in the scene to
avoid collision with the woman
●
Kinematic equation:
1
2
1
2
●
=
 +  
●
=
●
 = 28.96635
38.6218 + 0 1.5
Time the bus should take to stop
if it does only have about 5m like
the scene
1
2
5 = 38.6218 + 0 
5 = 19.3109
 = .2589
Determining the force needed to stop
the bus in the scene
Coefficient of friction:
Fnet=Fapp-Fk= µFn
−
• Fnet=ma (acceleration=
)
0−38.6218

Fnet=20,360(
)
.5
Fnet=1,572,679.696N
•
Rubber on wet concrete: µs=0, µk=.5
Fk=µkFn (Fn=mg)
Fk=.5(20,360×9.81)
Fk=99,865.8N
•
Fnet=Fapp-Fk
1,572,679.696=Fapp-99,865.8
Fapp=1,672,545.496N
~1,6722.5455kN to stop the bus
Harry would crash through the windshield
during brake of the bus
Momentum: F∆t=mvf-mvi
=
(70×0)−(70×38.6218)
.055 (  )
−2,703.526
.055
=
 = −49,155.0181
-Convert into lbs /10 ×2.2= 10,814.104lbs
120-200N/mm2 =Force needed to break a windshield
●
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The braking force of this speed is too great for the bus
The stopping distance of the bus going this velocity would require a much longer
stopping distance
–
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The time is still wrong in order to stop within this distance
●
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Only a quarter of a second of time can pass to have a 5m stopping distance
The force to stop in the movie does not match up with the actual force it would take
the bus to stop
–
●
~5m in movie, but it would need 28.97m
~524kN to stop in the movie, it should take ~1,000kN to stop in real life
Harry should fly through the windshield after stopping that instantly
–
49,155.0181N of force greatly exceeds the 120-200N Force needed to break a
windshield
Works Cited
●
●
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"AEC Regent III RT." Wikipedia. Wikimedia Foundation,
25 Mar. 2012. Web. 04 Apr. 2012.
<http://en.wikipedia.org/wiki/AEC_Regent_III_RT>
"City Blocks Differ in Size." Click Here to Support Our
Advertiser. Web. 20 Apr. 2012.
<http://www.land4ever.com/block.htm>.
"Knight Bus." Knight Bus- Hary Potter Wiki. Wikja
Entertainment. Web. 4 Apr. 2012.
<http://harrypotter.wikia.com/wiki/Knight_Bus>.
Works Cited
●
●
"London Bus Museum." 1952 AEC Regent III Bus â€
“
RT3491 -. The London Bus Preservation Trust Ltd. Web. 04
Apr. 2012. <http://www.londonbusmuseum.com/museumexhibits/double-deck-buses/aec-regent-iii-rt-rt-3491/>.
Yirka, Tonya. "Tempered Glass Strength Specifications."
EHow. Demand Media, 29 Nov. 2010. Web. 21 Apr. 2012.
<http://www.ehow.com/list_7575774_tempered-glassstrength-specifications.html>.
Works Cited
Pictures:
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http://news.bbc.co.uk/cbbcnews/hi/pictures/galleries/newsid_2821000/2821417.stm
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http://www.google.com/imgres?q=the+knight+bus&um=1&hl=en&sa=N&qscrl=1&nord=1&rlz=1T4ADSA_enUS373US374&biw=1024&bih=569&tbm=isch
&tbnid=BOtF3rh9PhTGXM:&imgrefurl=http://wizardinglife.com/2011/09/wizarding-methods-of-travelevaluated/&docid=v_yLM3MO1TWT9M&imgurl=http://wizardinglife.com/wp-content/uploads/2011/09/knightbus.jpg&w=400&h=339&ei=kwWWT_zXE4qN6QHopDGDg&zoom=1&iact=rc&dur=171&sig=112332215653833233722&page=2&tbnh=170&tbnw=219&start=8&ndsp=13&ved=1t:429,r:2,s:8,i:110&tx=134&ty=
157
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http://www.google.com/imgres?q=harry+potter+and+the+prisoner+of+azkaban&um=1&hl=en&sa=X&qscrl=1&nord=1&rlz=1T4ADSA_enUS373US374&biw
=1024&bih=569&tbm=isch&tbnid=TK_tNWBTIEnggM:&imgrefurl=http://www.rottentomatoes.com/m/harry_potter_and_the_prisoner_of_azkaban/&docid=n
HOXaARcUHyfM&imgurl=http://content6.flixster.com/movie/10/93/71/10937100_det.jpg&w=180&h=266&ei=1waWT9SoCuW26QH26ryODg&zoom=1&iact=r
c&dur=688&sig=112332215653833233722&page=1&tbnh=165&tbnw=112&start=0&ndsp=13&ved=1t:429,r:16,s:0,i:139&tx=88&ty=108
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http://wiki.answers.com/Q/What_is_the_weight_of_a_double_decker_bus
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http://hypertextbook.com/facts/2006/DanielTouger.shtml
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http://www.google.com/imgres?q=the+knight+bus&start=188&um=1&hl=en&biw=1249&bih=592&addh=36&tbm=isch&tbnid=Bg0buyu5CRoFM:&imgrefurl=http://news.bbc.co.uk/cbbcnews/hi/pictures/galleries/newsid_3552000/3552585.stm&docid=h3sAspCViRAUM&imgurl=http://news.bbc.co.uk/media/images/39963000/jpg/_39963687_harryonknightbus2.jpg&w=350&h=250&ei=ar2gT4fBAaT50gGB642yCQ&
zoom=1&iact=rc&dur=292&sig=107901962098801536091&page=8&tbnh=141&tbnw=201&ndsp=26&ved=1t:429,r:6,s:188,i:18&tx=147&ty=52
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http://www.google.com/imgres?q=physics&start=217&um=1&hl=en&sa=N&biw=1249&bih=592&addh=36&tbm=isch&tbnid=M1IdrwrZHlo7fM:&imgrefurl
=http://www.e-radiography.net/radsafety/rad_physics.htm&docid=KedQ4_IAiBoCHM&imgurl=http://www.eradiography.net/radsafety/rad_physics2.gif&w=332&h=400&ei=RsOgT9GwL4G0gwfj4YyRCQ&zoom=1&iact=hc&vpx=387&vpy=109&dur=650&hovh=246
&hovw=204&tx=55&ty=132&sig=107901962098801536091&page=9&tbnh=136&tbnw=85&ndsp=29&ved=1t:429,r:16,s:217,i:100
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http://www.google.com/imgres?q=conclusion&um=1&hl=en&biw=1249&bih=592&tbm=isch&tbnid=BZlppWzngyGCM:&imgrefurl=http://taufikthebeta.blogspot.com/2012/02/drawing-conclusion.html&docid=PE8Ye5HWDUO5oM&imgurl=http://1.bp.blogspot.com/ZTZzH7VhUT4/T0oqLgb4JI/AAAAAAAAAFY/UlkCQiZI0hI/s400/fc9conclusion_imagen.jpg&w=358&h=283&ei=jcWgT8CjDtC_gQetyYSqCQ&zoom=1&iact=hc&vpx=528&v
py=166&dur=1915&hovh=200&hovw=253&tx=121&ty=120&sig=107901962098801536091&page=1&tbnh=105&tbnw=131&start=0&ndsp=24&ved=1t:429,
r:3,s:0,i:139
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http://www.google.com/imgres?q=the+knight+bus&start=123&um=1&hl=en&safe=active&sa=N&tbm=isch&tbnid=GLig9Xc8lzlZSM:&imgrefurl=http://wizardinglife.com/
2011/01/loved-ones-say-goodbye-to-beloved-knight-bus-driver/&docid=skhwNqaYBwJi5M&imgurl=http://wizardinglife.com/wpcontent/uploads/2011/01/jimmy_gardner_news_jpg_display.jpg&w=300&h=217&ei=UauWT9faCOXh0QHZvIHTDg&zoom=1&biw=1280&bih=599&iact=rc&dur=344&sig=
108550289589178820660&page=6&tbnh=126&tbnw=173&ndsp=26&ved=1t:429,r:4,s:123,i:66&tx=90&ty=101
http://www.google.com/imgres?q=harry+potter+and+the+prisoner+of+azkaban&um=1&hl=en&sa=N&biw=1249&bih=592&tbm=isch&tbnid=h4D7ENHgA4v_M:&imgrefurl=http://www.fanpop.com/spots/harry-potter/images/5026234/title/harry-potter-prisonerazkaban&docid=1VxBRpr2wB3P8M&imgurl=http://images2.fanpop.com/images/photos/5000000/Harry-Potter-and-the-Prisoner-of-Azkaban-harry-potter-5026234-720480.jpg&w=720&h=480&ei=4rqgT77EEsaPgwf7g72mCQ&zoom=1&iact=hc&vpx=280&vpy=282&dur=642&hovh=183&hovw=275&tx=180&ty=140&sig=10790196209880
1536091&page=3&tbnh=124&tbnw=165&start=54&ndsp=26&ved=1t:429,r:14,s:54,i:288
http://www.google.com/imgres?q=the+knight+bus&um=1&hl=en&biw=1249&bih=592&tbm=isch&tbnid=LWLXySw5O6_sPM:&imgrefurl=http://www.hplexicon.org/wizworld/knight_bus.html&docid=Cv_EwDrkftqLAM&imgurl=http://www.hp-lexicon.org/images/chapters/pa/c03--the-knightbus.jpg&w=350&h=334&ei=jbygT8XqNcbg0QH__vGcCQ&zoom=1&iact=rc&dur=103&sig=107901962098801536091&page=1&tbnh=109&tbnw=114&start=0&ndsp=24&
ved=1t:429,r:0,s:0,i:81&tx=61&ty=67
http://www.google.com/imgres?q=the+knight+bus&um=1&hl=en&biw=1249&bih=592&tbm=isch&tbnid=pIUVUzUoFFuRpM:&imgrefurl=http://www.david-edwardbyrd.com/warners7-3.html&docid=RIAblzz4qEXKqM&imgurl=http://www.david-edward-byrd.com/gallery/warners7-3lrg.jpg&w=300&h=392&ei=jbygT8XqNcbg0QH__vGcCQ&zoom=1&iact=rc&dur=217&sig=107901962098801536091&page=2&tbnh=138&tbnw=113&start=24&ndsp=28&
ved=1t:429,r:1,s:24,i:141&tx=77&ty=117
http://www.google.com/imgres?q=wet+road&um=1&hl=en&biw=1249&bih=592&tbm=isch&tbnid=JvqOtqYsTtpBuM:&imgrefurl=http://www.wunderground.com/wxim
age/viewsingleimage.html%3Fmode%3Dsingleimage%26handle%3Dgemini%26number%3D1227&docid=zl3gLEiMFwJw_M&imgurl=http://iconsak.wunderground.com/data/wximagenew/g/gemini/1227.jpg&w=640&h=421&ei=i76gT5qlKeT40gH7vp2LCQ&zoom=1&iact=hc&vpx=94&vpy=177&dur=122&hovh=182
&hovw=277&tx=160&ty=111&sig=107901962098801536091&page=1&tbnh=112&tbnw=149&start=0&ndsp=21&ved=1t:429,r:0,s:0,i:120
http://www.google.com/imgres?q=shattered+glass&um=1&hl=en&biw=1249&bih=592&tbm=isch&tbnid=V7FPEdym0sYXwM:&imgrefurl=http://newmichael.com/shatte
red-glass&docid=FfjZHDoREwHk9M&imgurl=http://newmichael.com/wp-content/uploads/2012/02/Shattered-Glass2.jpg&w=400&h=300&ei=-cOgT-nlIpKgAemwuC7CQ&zoom=1&iact=hc&vpx=358&vpy=173&dur=1121&hovh=194&hovw=259&tx=152&ty=128&sig=107901962098801536091&page=1&tbnh=114&tbnw=152
&start=0&ndsp=23&ved=1t:429,r:2,s:0,i:137
http://www.google.com/imgres?q=woman+in+front+of+bus&um=1&hl=en&biw=1249&bih=592&tbm=isch&tbnid=Hc7bYlCtuLYvtM:&imgrefurl=http://newsfeed.time.co
m/2011/10/21/a-new-york-city-bus-gives-women-the-backseat/&docid=uGoBMatDfIhvkM&imgurl=http://timenewsfeed.files.wordpress.com/2011/10/new_york_bus.jpg%253Fw%253D455%2526h%253D376%2526crop%253D1
&w=455&h=376&ei=F8WgT9pmj7vQAa7m5akJ&zoom=1&iact=rc&dur=1&sig=107901962098801536091&page=1&tbnh=122&tbnw=148&start=0&ndsp=21&ved=1t:429
,r:14,s:0,i:97&tx=100&ty=41

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