physics and astronomy outreach program at the university of british columbia physics and astronomy...
TRANSCRIPT
Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia
Lecture Notes
Animals
Falling Cats
Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia
• Physics: Develop concept of air drag and investigate how it affects free fall and results in a terminal velocity.
• Biology: To understand how air drag partially explains why cats sustain less damages after a free fall than a human.
Falling CatsGoals
Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia
• Physics: Air resistance determines a terminal velocity which depends on cross-sectional area and mass.
• Biology: Cats have a different cross-sectional area and mass than humans.
Falling CatsBig Ideas
Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia
• A drag force exists opposite to the motion due to air resistance
Falling CatsDrag
2
2
1AvCD D
A
v
= cross-sectional area
= density of air = 1.29 kg/m3
= speed
DC = drag coefficient 0.5
Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia
• A falling object experiences the force of gravity and drag.
Falling CatsDrag
2
4
1AvD
mgFg
2
4
1AvmgFnet
Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia
• Terminal velocity is reached when
Falling CatsTerminal Velocity
2
4
1AvD
mgFg
Fnet mg1
4Av term
2
0 mg 14
Av term2
A
mgvterm
4
0netF
Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia
Falling CatsCalculation
m/s35)1.0)(29.1(
)8.9)(1.4)(4(4
A
mgvcatterm
kg1.4m22 m1.0m)1.0)(2.0( A
• For a cat falling flat:
Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia
• For a human falling flat:
Falling CatsCalculation
m/s56)64.0)(29.1(
)8.9)(65)(4(4
A
mgvhumanterm
kg65m22 m64.0m)6.1)(4.0( A
Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia
Falling CatsComparison
m/s56humantermv<m/s35cat
termv
• Cats hit the ground at a lower velocity,
• The anatomy of a cat having four legs allows them to lengthen the deceleration time during impact compared to a human
t
vmmaFimpact
catimpactF < human
impactF