Lecture 16 Friday, October 3

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# Lecture 16 Friday, October 3 - PowerPoint PPT Presentation

Lecture 16 Friday, 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.

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### 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 parallel to the velocity
• Is directed towards the center of the circle
• 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.

Chapter 6

Circular Motion, Orbits and Gravity

Topics:

• The kinematics of uniform circular motion
• The dynamics of uniform circular motion
• Circular orbits of satellites
• Newton’s law of gravity

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
Circular Motion
• Note similarity to the equations for one-dimensional linear motion
UCM continued
• Travelling at constant speed v around circle
• Period is time one around circle = T
UCM cont
• s is distance travelled around circumference and the definition of the radian tell us
Uniform Circular Motion
• Uniform magnitude of velocity (speed) ω, is constant
• But α is not zero because direction of velocity is changing.
Newton’s Second Law
• Net force must point towards center of circle

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

Checking Understanding

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?
• Tangent to the circle, in the direction of the ball’s motion
• Toward the center of the circle

Slide 6-11

Problems due today
• 5: 24, 25, 29, 30, 31, 35, 36, 37, 39