physics 1a, section 6
DESCRIPTION
Physics 1A, Section 6. October 6, 2008. Section Business. Section 6 office hour: Caltech/Downs 101 Tuesdays 4:00 - 5:30 PM See other choices on course web site: http://www.its.caltech.edu/~tmu/ph1a Section web site: http://www.submm.caltech.edu/~cdd/PHYS1A_2008. - PowerPoint PPT PresentationTRANSCRIPT
Physics 1A, Section 6
October 6, 2008
Section Business
• Section 6 office hour:– Caltech/Downs 101– Tuesdays 4:00 - 5:30 PM
• See other choices on course web site:– http://www.its.caltech.edu/~tmu/ph1a
• Section web site:– http://www.submm.caltech.edu/~cdd/PHYS1A_2008
Week 1 Reading/Lecture Review• T.M.U. chapters 1-2 + lectures:
– units & dimensions– dimensional analysis (estimation)– law(s) of falling bodies
• constant acceleration (compare eq. 2.14-2.16): s = s0 + v0t + ½ at2
v = v0 + at
– distance, velocity, acceleration (general case):• v = ds/dt• a = dv/dt
• Oresme (14th century): v t
s t2
(both correct)
A modern look athistorical laws of falling bodies
A modern look athistorical laws of falling bodies• Galileo (17th century):
time 1 2 3 4 5 …
s 1 3 5 7 9 …
• Galileo (17th century):
time 1 2 3 4 5 …
s 1 3 5 7 9 …
s 1 4 9 16 25 …
A modern look athistorical laws of falling bodies
• Galileo (17th century):
s t2 (correct)
time 1 2 3 4 5 …
s 1 3 5 7 9 …
s 1 4 9 16 25 …
A modern look athistorical laws of falling bodies
• da Vinci (15th century):
time 1 2 3 4 5 …
s 1 2 3 4 5 …
A modern look athistorical laws of falling bodies
• da Vinci (15th century):
time 1 2 3 4 5 …
s 1 2 3 4 5 …
s 1 3 6 10 15 …
A modern look athistorical laws of falling bodies
• da Vinci (15th century):
s (t)(t + 1)/2 = t2/2 + t/2
time 1 2 3 4 5 …
s 1 2 3 4 5 …
s 1 3 6 10 15 …
A modern look athistorical laws of falling bodies
• da Vinci (15th century):
s (t)(t + 1)/2 = t2/2 + t/2
v = ds/dt t + 1/2 (moving at the start)
time 1 2 3 4 5 …
s 1 2 3 4 5 …
s 1 3 6 10 15 …
A modern look athistorical laws of falling bodies
• Albert of Saxony (14th century): v s
A modern look athistorical laws of falling bodies
• Albert of Saxony (14th century): v s
ds/dt = ks
A modern look athistorical laws of falling bodies
• Albert of Saxony (14th century): v s
ds/dt = ks s = Cekt
A modern look athistorical laws of falling bodies
• Albert of Saxony (14th century): v s
ds/dt = ks s = Cekt
v = Ckekt
A modern look athistorical laws of falling bodies
• Albert of Saxony (14th century): v s
ds/dt = ks s = Cekt
v = Ckekt
Takes an infinite time to start from infinitesimal velocity!
A modern look athistorical laws of falling bodies
Quiz Problem
35
Quiz Problem
35
• Answer:
a) a(t) = jt + a0
v(t) = jt2/2 + a0t + v0
x(t) = jt3/6 + a0t2/2 + v0t + x0
b) (see graph)
c) A was ahead at t = 0.5 s.
d) J will win.0 0.5 1 1.5
time (s)
x
Car A
Car J
Quiz Problem
46
Quiz Problem
46• Answer:
a) D’ = VsT
= sqrt{W2 + (X-VrT)2}
b) tan ‘ = (X-VrT)/W
c) Vs > Vr
d) (Vs2-Vr
2)T2 + 2XVrT – (W2+X2) = 0
Use quadratic formula.
e) T = W/sqrt{Vs2-Vr
2}
f) T = W/Vs
X = WVr/Vs
Thursday, October 9:
• T.M.U., Problem 3-7
• Quiz Problem 19
• Optional, but helpful, to look at these in advance.