Physics 1A, Section 6

1. Physics 1A, Section 6 October 6, 2008

2. 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

3. 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

4. A modern look athistorical laws of falling bodies • Oresme (14th century): v  t s  t2 (both correct)

5. A modern look athistorical laws of falling bodies • Galileo (17th century):

6. A modern look athistorical laws of falling bodies • Galileo (17th century):

7. A modern look athistorical laws of falling bodies • Galileo (17th century): s  t2 (correct)

8. A modern look athistorical laws of falling bodies • da Vinci (15th century):

9. A modern look athistorical laws of falling bodies • da Vinci (15th century):

10. A modern look athistorical laws of falling bodies • da Vinci (15th century): s  (t)(t + 1)/2 = t2/2 + t/2

11. 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)

12. A modern look athistorical laws of falling bodies • Albert of Saxony (14th century): v  s

13. A modern look athistorical laws of falling bodies • Albert of Saxony (14th century): v  s ds/dt = ks

14. A modern look athistorical laws of falling bodies • Albert of Saxony (14th century): v  s ds/dt = ks s = Cekt

15. A modern look athistorical laws of falling bodies • Albert of Saxony (14th century): v  s ds/dt = ks s = Cekt v = Ckekt

16. 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!

17. Quiz Problem 35

18. 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.

19. Quiz Problem 46

20. Quiz Problem 46 • Answer: • a) D’ = VsT • = sqrt{W2 + (X-VrT)2} • b) tan q‘ = (X-VrT)/W • c) Vs > Vr • d) (Vs2-Vr2)T2 + 2XVrT – (W2+X2) = 0 • Use quadratic formula. • e) T = W/sqrt{Vs2-Vr2} • f) T = W/Vs • X = WVr/Vs

21. Thursday, October 9: • T.M.U., Problem 3-7 • Quiz Problem 19 • Optional, but helpful, to look at these in advance.