Lecture 16 Friday, October 3
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Transcript of Lecture 16 Friday, October 3
Lecture 16Friday, October 3
Chapter 6:Circular Motion
Review Example
Macie pulls a 40 kg rolling trunk by a strap angled at 30° from the horizontal. She pulls with a force of 40 N, and there is a 30 N rolling friction force acting on trunk. What is the trunk’s acceleration?
Slide 5-17
For uniform circular motion, the acceleration
Is paralle
l to th
e velocity
Is dire
cted to
wards the ...
is lar
ger for a
larger o
rbit...
33% 33%33%1. Is parallel to the velocity
2. Is directed towards the center of the circle
3. is larger for a larger orbit at the same speed
Problem, interacting bodies
Glider on a air track
Massless, frictionless pulley
m1
m2
Special Assignment
• Special assignment to be handed in Monday: Workbook pages 4-5 and 4-6, exercises 17-22 and page 5-5, exercises 13-15.
• The kinematics of uniform circular motion
• The dynamics of uniform circular motion
• Circular orbits of satellites
• Newton’s law of gravity
Chapter 6Circular Motion, Orbits and Gravity
Topics:
Sample question:The motorcyclist in the “Globe of Death” rides in a vertical loop upside down over the top of a spherical cage. There is a minimum speed at which he can ride this loop. How slow can he go?
Slide 6-1
Uniform Circular Motion
• Uniform magnitude of velocity (speed) is constant
( )( )
( )
t angular positiond tangular velocity
t dtd tangular acceleration
t dt
Circular Motion
• Note similarity to the equations for one-dimensional linear motion
( )( )
( )( )
x displacementx dx tv t velocityt dt
v dv ta t accelerationt dt
• Going from angular velocity to angular displacement:
1 where is frequency (rad/s)
2 rad for uniform circular motion
f i t
T period ff
T
UCM continued
• Travelling at constant speed v around circle• Period is time one around circle = T
2vT rv r
UCM cont
• s is distance travelled around circumference and the definition of the radian tell us
thens rv ra r
Uniform Circular Motion
• Uniform magnitude of velocity (speed) ω, is constant
• But α is not zero because direction of velocity is changing.
22v r
r
Uniform Circular Motion
Slide 6-13
Newton’s Second Law
• Net force must point towards center of circle
2
, toward center of circleNETmvF mar
Example
A level curve on a country road has a radius of 150 m. What is the maximum speed at which this curve can be safely negotiated on a rainy day when the coefficient of friction between the tires on a car and the road is 0.40?
Slide 6-24
Top View
• v
sf
When a ball on the end of a string is swung in a vertical circle:What is the direction of the acceleration of the ball?
A. Tangent to the circle, in the direction of the ball’s motion
B. Toward the center of the circle
Checking Understanding
Slide 6-11
Problems due today
• 5: 24, 25, 29, 30, 31, 35, 36, 37, 39