« December 2009 »
S M T W T F S
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30 31
You are not logged in. Log in
Entries by Topic
All topics
Ch 13
Chap 10
Chap 11
Chap 14
Chap 15
Chap 16
Chap 18
Chap 19
Chap 20
Chap 25
Chap 26
Chap 27
Chap 28
Chap 29
Chap 30
Chap 4
Chap 5
Chap 6
Chap 7
Chap 8
Chap 9  «
Chapter 12
Final Exam
Physics Club
Project
Weekly Plans
Blog Tools
Edit your Blog
Build a Blog
RSS Feed
View Profile
Group One
Tripod Home
Tripod Build
Tripod Member Spotlight
Register Your Domain
Group Two
Lycos Home
Lycos Search
Lycos News
Monday, 18 December 2006
Chap 9 Notes page 1
Now Playing: 9.1 to 9.3
Topic: Chap 9
9.1 Rotation and Revolution 

Rotation: 

q       the axis of rotation is located within the body of the object

q       the object rotates 

Revolution: 

q       the axis of rotation is external

q       Objects revolve about the axis

 

9.2 Rotational Speed

 

Linear speed

q       What we have already studied

q       Distance/time

q       Greater on the outer edge of a rotating object

q       Called tangential speed for a rotating object

q       Tangential speed ~ radius  x  rotational speed

 

Rotational speed

q       Also called angular speed

q       The number of rotations per unit of time

q       All parts of the rotating object have the same rotational speed

q       RPM is a common unit:  means revolutions per minute

 Question:
  1. Which part of the earth’s surface has the greatest rotational speed about the earth’s axis? 
  2. Which part has the greatest linear speed  relative to the earth’s axis?
  3. On a particular merry-go-round, the horses along the outer rail are located three times farther from the axis of rotation than the horses along the inner rail.  If a boy sitting on a horse near the inner rail has a rotational speed of 4 RPM and a tangential speed of 2 m/s, what will be the rotational speed and tangential speed of his sister who is sitting on a horse along the outer rail?
Trains ride on a pair of tracks.  For straight-line motion, both tracks are the same length.  But which track is longer for a curve, the one on the outside or the one on the inside of the curve?

Posted by physicscp at 2:11 PM EST
Chap 9 Notes continued
Now Playing: 9.3 to 9.5 Notes
Topic: Chap 9

9.3 Centripetal Force 

Centripetal Force is

q       any force that causes an object to follow a circular path.

q       Directed at a right angle to the path of a moving object

q       Gravitational and electrical forces act as centripetal forces in certain situations.

 

See figure 9.5 on page 127 for Centripetal Force acting on a car rounding a curve.

 9.4 Centripetal and Centrifugal Forces 

In figure 9.6 the clothes are forced into circular motion but the water is not.

 

In figure 9.7 when the string breaks the can moves in a straight line

 

Centrifugal force is

q       An outward force on an object in circular motion

q       Really a fictitious force resulting from change in inertia

 

In figures 9.8 to 9.10 the whirling can provides the illusion of centrifugal force and the illusion of “gravity”

 9.5    Centrifugal Force in a Rotating Reference Questions 
  1. A heavy iron ball is attached by a spring to a rotating platform.  Two observers, one in the rotating frame of reference and one on the ground at rest, observe its motion.  Which observer sees the ball being pulled outward, stretching the spring?  Which observer sees the spring pulling the ball into circular motion?
  2. The spring in the sketch stretches 10 cm when the ball is located midway between the axis and the outer edge of the rotating circular platform.  The spring support is then moved so the ball is located directly over the platform’s outer edge, effectively doubling the ball’s distance from the axis.  Will the spring stretch more than, less than or the same (10 cm) as it did before the support was moved?

Posted by physicscp at 2:06 PM EST

Newer | Latest | Older