Welcome back to Physics 211

1
Welcome back to Physics 211

• Todays agenda
• Midterm 1 Thursday 10/1
• Review session Wednesday 9/30/09 Stolkin
  Auditorium 700 pm - SPS
• Motion in 2-D (Circular, relative)
• Read ch. 4 complete!

2
Exam 1 Thursday (10/1/09)

• During normal lecture period, 1100AM - 1220 pm
  in Stolkin Auditorium.
• Seating arrangement by last name will be posted
  outside Stolkin.
• Exam is closed book, but you may bring calculator
  and one handwritten 8.5 x 11 sheet of notes.
• Practice exam problems posted on website and
  Wednesday in recitation workshop.
• Review session (SPS) -- Wednesday, 7 - 8 pm,
  Stolkin Auditorium

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Exam 1 Thursday (10/1/2009)

• Seating arrangement will be posted outside
  Stolkin
• Material covered
• Textbook chapters 1, 2, 3, and 4
• Lectures up to 9/29 (slides online)
• Workshops on Velocity, Acceleration in one
  dimension, and Motion in two dimensions
• Homework assignments

4
Skill Set Mastery

• Draw a Motion Diagram
• Construct a s-t graph
• Construct a v-t graph
• Describe the motions

5
Projectile Motion
Projectile motion is made up of two independent
motions uniform motion at constant velocity in
the horizontal direction and free-fall motion in
the vertical direction. The kinematic equations
that describe these two motions are
6
Motion Along Curved Paths
Ds sf - si
sI
sF
O
v Ds/Dt lies along dotted line. As Dt ?
0 direction of v is tangent to path
7
Motion on a curved pathat constant speed
8
A biker is riding at constant speed clockwise on
the oval track shown below. Which vector
correctly describes the acceleration at the point
indicated?
9
Biker moving around oval at constant speed
As point D is moved closer to C, angle approaches
90.
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Summary

• For motion at constant speed, instantaneous
  acceleration vector is perpendicular to velocity
  vector
• Points inward
• What is the magnitude of the acceleration vector?

11
Acceleration vectors for ball swung in a
horizontal circle at constant speed v
v1
? q
v2
R
v1
?q
v2
What is the magnitude of the acceleration??a?
v2/R
12
Angular Displacement and Derivatives
??, ??/ ?t
?
t
13
Acceleration of object moving at constant speed
on a circular path
Acceleration depends on radius of circle.
14
What if the speed is changing?

• Consider acceleration for object on curved path
  starting from rest
• Initially, v2/r 0, so no radial acceleration
• But a is not zero! It must be parallel to
  velocity

15
Acceleration vectors for object speeding
upTangential and radial components(or parallel
and perpendicular)
16
Sample problem

• A Ferris wheel with diameter 14.0 m, which
  rotates counter-clockwise, is just starting up.
  At a given instant, a passenger on the rim of the
  wheel and passing through the lowest point of his
  circular motion is moving at 3.00 m/s and is
  gaining speed at a rate of 0.500 m/s2. (a) Find
  the magnitude and the direction of the
  passengers acceleration at this instant. (b)
  Sketch the Ferris wheel and passenger showing his
  velocity and acceleration vectors.

17
Angular Acceleration
?
t
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Table 4.1 p. 116
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Homework

• Chapter 4 text Due Tuesday 9/29 (not collected)
• EP 21, 22, 27, 36, 62, 63, 67, 71