Welcome back to Physics 211

1
Welcome back to Physics 211

• Todays agenda
• Midterm 1 Thursday 9/25
• Review session Wednesday 9/24/08 Stolkin
  Auditorium 600 pm - SPS
• Vector components
• Motion in 2-D
• Read ch.3
• Read ch. 4 complete!

2
Exam 1 Thursday (9/25/08)

• 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, 6 - ? pm,
  Stolkin Auditorium

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Exam 1 Thursday (9/25/08)

• Seating arrangement will be posted outside
  Stolkin
• Material covered
• Textbook chapters 1, 2, 3, and 4
• Lectures up to 9/23 (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
Simultaneous Projectile

• Demo
• Which hits first?
• 1 Straight down
• 2 Straight out
• 3 Same time
• 4 Not enough information
• 5 Depends on vx

6
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
7
Car driving off cliff
How far away does the car land? What is the
velocity when it lands? How long is it in the air?
8
Demo Hit the Pitt Panther!

• How far away must we be if our cannon is aimed
  20 above horizontal and fires with v 9.2 m/s?

If you shoot like your quarterback, Im safe,
hahahahaha
9
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
10
Motion on a curved pathat constant speed
11
A child is riding a bicycle on a level street.
The velocity and acceleration vectors of the
child at a given time are shown. Which of the
following velocity vectors may represent the
velocity at a later time?
a
1. 2. 3. 4.
12
A biker is riding at constant speed clockwise on
the oval track shown below. Which vector
correctly describes the acceleration at the point
indicated?
13
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?

15
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
16
Angular Displacement and Derivatives
??, ??/ ?t
?
t
17
Acceleration of object moving at constant speed
on a circular path
Acceleration depends on radius of circle.
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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

19
Acceleration vectors for object speeding
upTangential and radial components(or parallel
and perpendicular)
20
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.

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Angular Acceleration
?
t
22
Table 4.1 p. 116
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Homework

• Chapter 4 text
• EP 5, 6, 11, 12, 45
• EP 21, 22, 27, 36, 63