LESSON 4

PHYS LESSON 4 FOR
MONDAY, June 7, 2010

I Introduction

II Logistics

III Return of tests, labs, papers; collection of overdue assignments

IV Running Grades

V Review of Lesson 3: Circular motion
a. v = 2pr/P Э 2pr = c (circumference); r = radius; P = period, in seconds, to make one trip around the circle; and P = 1/n, Э n = the frequency in cycles per second (Hz).

b. v2/r = 4p2r/P2, but since P = (1/n), then P2 = (1/ n)2, or (1/P2) = n2


c. So, v2/r = 4p2rn2 which can be written as v2/r = (2pn)2 r

d. And, in circular motion, a = v2/r =
(2pn)2 r, “centripetal acceleration”
e. However, 2pn = w in rad/sec, thus a = w2r

f. If part of a circle, say, s, is the arc, AB, then we can say that for small “s” that r sinθ = s, and if it’s even smaller, then r θ = s because for small θ, sin θ = θr where the angle, θ, is measured in radians, not degrees. 360° = 2p radians, so 1 radian = 57.3°.

g. Since v = dist/time, then v = s/t = r (θ/t) but is another way of writing (θ/t) = w, so
v = wr and v2/r = w2r = a, “acceleration”


VI Laboratory Exercise 3: Linear Motion

VII Lesson 4: Newton's Laws of Motion

VIII Conclusion
A. HWK Assignment 2: due 6/10
B. Essay 2: Sir Isaac Newton, due 6/10