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circular motion
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- 2. ROTATIONAL MOTION Objectsthat spin undergo rotational motion. Any point on the object has circular motion around the axis. The direction of of motion is constantly changing.
- 3. ROTATIONAL QUANTITIES - angular displacement –(degrees, radians, or revolutions) = s/r - angular speed (rads/sec) = /t - angular acceleration (rads/sec2) = /t 1 radian = 57.3 o 2 rads = 1 rev = 360 o
- 4. Practice Problem Whileriding on a carousel that is rotating clockwise, a child travels through an arc length of 11.5 m. If the child’s angular displacement is 165 o , what is the radius of the carousel?
- 5. Practice Problem Achild at an ice cream parlor spins on a stool. The child turns counterclockwise with an average angular speed of 4.0 rads/sec. In what time interval will the child’s feet have an angular displacement of 8.0 rad?
- 6. Practice Problem Thewheel on an upside down bicycle moves through 11.0 rad in 2.0 s. What is the wheel’s angular acceleration of its initial angular speed is 2.0 rad/s?
- 7. Tangential Speed Instantaneouslinear speed Varies with position from axis of rotation Speed along a line drawn tangent to the circular path v t = r v t = 2 r/T T is period (time/# revolutions)
- 8. Tangential Acceleration Tangentto circular path Occurs when rotating objects change speed Example: A carousel speeds up a t = r
- 9. Practice Problem Whatis the tangential speed of a child seated 1.2 m from the center of a rotating merry go round that makes one complete revolution in 4.0 s? It takes 2.5 s for the merry go round to slow to a speed of .75 m/s. What is the tangential acceleration?
- 10. Centripetal Acceleration Occursas object moves in a circular path because it changes direction Is constant or uniform Directed toward the center a c = v t 2 a c = r 2 r
- 11. Total Acceleration Whenboth centripetal and tangential acceleration exist, a t is tangent to circular path a c is toward the center Components are perpendicular a total = square root of a c 2 + a t 2 Direction = tan = a c /a t a total a c a t
- 12. Practice Problem ThePolar Express has an angular acceleration of .50 rad/s/s. A rider sits 6.6 m from the center and makes 10 revolutions in 13 seconds. Find the tangential, centripetal, and total accelerations.
- 13. Circular Motion objectmoves in a circular path Continuous uniform acceleration Ex: ball on the end of a string, Moon moving about the Earth (almost circular) Can be vertical or horizontal animation by Behrooz Mostafavi
- 14. Vertical Circular motionFw Fw Ft Ft V min occurs at the top V = square root of rg Ex: loop roller coaster
- 15. Practice Problem Aball of mass .45 kg is swung in a vertical circle. If the centripetal force on the ball is 12.5 N, what is the tension in the string at the top and bottom of the circle?
- 16. How do youfeel… when sitting on the outside of the Polar Express ride at the State Fair when you are in a car that turns sharply to the left. What causes these feelings?
- 17. Centrifugal Force –not real
- 18. Centripetal Force –the real force
- 19. Explain how abucket of water can be whirled in a a vertical circle without the water spilling out, even at the top of the circle when the bucket is upside down.
- 20. Horizontal Circular motionTension force acts horizontal and is constant. If weight is small enough it can be ignored. Ex: polar express
- 21. Centrifugal Force thefake force
- 22. What will happen…when a car doesn’t have enough friction force to get around a curve?
- 23. If centripetal forceis inward why will water not fall our of a cup that is swung in a vertical path?
- 24. What is requiredto cause the ball to have a curved path?
- 25. Centripetal Force Requiredto maintain centripetal acceleration (Newton’s Laws) Directed toward the center Acts at right angles to motion Ex: gravity, friction, strings… F c = ma c = mr 2 = mv t 2 /r
- 26. Practice Problem Whatwould be the centripetal force on a 1500 kg car rounding a 8.5 m curve at a speed of 10.0 m/s?
- 27. It is sometimessaid that water is removed from clothes in the spin cycle by centrifugal force throwing the water outward. Is this correct?
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- 29. The smaller thevelocity of the object, the less centripetal force you will have to apply. The smaller the length of rope (radius), the more centripetal force you will have to apply to the rope .
- 30. The smaller themass, the smaller the centripetal force (shown by the red vector labeled as the force of tension in the rope, FT) you will have to apply to the rope.
- 31. If you letgo of the rope (or the rope breaks) the object will no longer be kept in that circular path and it will be free to fly off on a tangent.
- 32. Newton’s Law ofGravitation Planets move in nearly circular orbits about the sun Gravity acts as the centripetal force. Any two masses are attracted Inverse square law F g = Gm 1 m 2 r 2 G = 6.67 x 10 -11 Nm 2 /kg 2
- 33. Practice Problem Whatis the force of attraction between you and the Earth?
- 34. Pictures and animationsfrom http://regentsprep.org/Regents/physics/phys06/bcentrif/default.htm http://www.ap.smu.ca/demos/content/mechanics/waiters_tray/waiters_tray.html