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Chapter 9: Circular Motion

Chapter 9: Circular Motion. Axis. An axis is the straight line around which rotation takes place. Rotation. When an object turns about an internal axis. An axis located within the body of the object The motion is also called spin. Earth Rotates about its axis once every 24 hours.

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Chapter 9: Circular Motion

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  1. Chapter 9: Circular Motion

  2. Axis • An axis is the straight line around which rotation takes place

  3. Rotation • When an object turns about an internal axis. • An axis located within the body of the object • The motion is also called spin. • Earth Rotates about its axis once every 24 hours.

  4. Revolution • When an object turns about an external axis. • Earth Revolves around the sun once every 365¼ days.

  5. Linear Speed • What we simply called speed in Chapter 2. • A distance moved per unit time. • Linear speed varies based on radius of a circle. • On the Merry-Go-Round, the horses on the outermost ring have to travel faster to keep up with the horses that are closer to the center axis.

  6. Tangential Speed • The speed of something moving along a circular path. • We call it tangential motion because the speed is always tangent to the circle. • We can use tangential speed and linear speed as the same thing for circular motion.

  7. Rotational Speed • The number of rotations per unit of time. Symbol (ω-omega) • Sometimes called angular speed. • All parts of the merry-go-round rotate about their axis in the same amount of time. • Units for Rotational Speed = Rev. / second or Rev. / min. • The record player rotates with a rotational speed of 72,000RPM. • Tangential Speed = Radial dist x Rotational Speed v= r ω

  8. Centripetal Force • Any force that causes an object to follow a circular path. • Centripetal means “center seeking” or “toward the center.” • The force that holds the occupants in a rotating ride.

  9. Centrifugal Force • The Physics curse word!!! • Very commonly misused. • Means “center-fleeing” or “away from the center.” • Misconception that centrifugal force pulls you outward during circular motion. • Actual force is just the inertia of the body traveling tangent to the circle.

  10. As a ball is whirled above the head, it is the inertia of the ball that wants to continue moving in a straight line. Instead, the ball is forced inward to change its direction (Centripetal Force-supplied by string).

  11. Simulated Gravity • When a wheel or apparatus is spun at just the right speed so that the acceleration feels like the gravity they are accustomed to.

  12. Equations to Note: • ac= v2/r • Fc = (mv2)/r • Vrotational = r ω = (2π r)/t

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