Rotation and Revolution. What’s the difference? Day 1: Circular Motion Definition of terms. Rotation and Revolution. What’s the difference? Rotation: when an object turns about an internal axis. Examples: carnival ride, turntable, and the earth’s rotation about their axes. Revolution: when an object turns about an external axis. Examples: The earth revolve around the sun once in 365.25 days/ 1 year.

Examples. Carnival ride is an example of____________ A bicycle wheel is an example of_________

Earth’s motion Rotating earth Revolving earth Earth rotates about its axis

Period and Frequency Period (T) is the time it takes for one full revolution or rotation of an object. Frequency (f): The number of rotations or revolutions per unit time. relationship between period and frequency is:

Linear speed/Tangential speed distance moved per unit time; Since circular distance is the circumference, tangential speed = Linear speed R

Rotational/Angular speed Rotational/Angular speed is the number of rotations per unit time. Example: Earth’s rotational speed is once in 24 hours,

Example: If the merry go round takes 2 seconds to make one rotation; for persons seated at A and B Calculate their linear speeds Calculate their angular speeds A B 2cm 2cm

Difference between linear and angular speeds. Notice that linear speed ____________with radius . While; Angular speed__________________

Class work: Textbook page 133, # 1-10.

Day 2: Centripetal Force: Centripetal Force is a center seeking force that keeps an object in a circular path Characteristics of circular motion F= centripetal Force. A= Centripetal acceleration V = tangential/linear velocity Both centripetal force and acceleration are directed toward the center of circular path. Motion is perpendicular to Force V A F

EXAMPLES OF CENTRIPETAL FORCE The friction force on the wheels provide the centripetal force necessary for turning a corner. The force of pulling provides the centripetal force that keeps the bucket in circular path.

Other examples The inner wall of the tub of a washing machine exerts a centripetal force on the wet clothes, the holes in the tub allows water to escape. Ladybug is held on the floor of a can by centripetal force provided by the circular moving can. Types of Forces - Circular Motion

Calculating centripetal acceleration The centripetal Acceleration of a circular moving object is given by: Where V is the linear/tangential speed The centripetal acceleration can be derived for the case of circular motion since the curved path at any point can be extended to a circle.

Example 1 The Moon’s nearly circular orbit about the Earth has a radius of about 384,000 km and a period T of 27.3 days. Determine the acceleration of the moon towards the Earth.

Example 2 A 150 g ball at the end of a string is revolving uniformly in a horizontal circle of radius 0.600 m. the ball makes 2 revolutions in a second. What is its centripetal acceleration?

Calculating centripetal Force From Newton’s second law; F=ma, The centripetal force is;

Day 3. Problem solving and review. Warm-up 60 kg Javier rides on a wheel that has a radius of 7.0 m. if the ride takes 20.0 seconds to make one full revolution, calculate the a) linear speed, b) centripetal acceleration, and c) centripetal force of the wheel.

Class work Textbook pg 135 # 31-35

Day 3:Warm up Determine the minimum speed a ball of mass 0.15 kg swung in a vertical circle of radius 1.3 m must have, so as to ensure it stays in its circular path when at the top of the arc.

Class work Workbook page 84 # 1-12

Day 4: Circular motion Lab

Day 5 Day 5: 12/11/12 Review: Workbook page 84 # 1-12 Complete Workbook pg 94 # A1-A4

Day. 6 Describe centrifugal force Centrifugal force is an outward-acting force useful only in a rotating frame of reference.

Centrifugal Vs Centripetal. Centrifugal force is directed away from the center (Center fleeing force) Centripetal force is directed towards the center (center seeking force)

Speed and centrifugal force. Increasing the speed increases the centrifugal force.

Centrifugal force is Fictitious. There is no mass pulling outward. A real force must have a source (mass). Centrifugal does not.

Simulated gravity Gravity can be simulated in a rotating space station if the rotation is regulated to produce a centripetal force equal to the weight of an object here on earth.

Looking ahead An orbiting space station from which space colonists would depart to the other research outposts. This station would be constructed of an assemblage of discarded space shuttle fuel tanks and "spun-up" to create an artificial gravity of 1g

Class work Class work Page 133, # 11-18 Homework: Textbook pg 134 # 19-30