Circular Motion

1. Circular Motion http://www.scicomics.com/uploads/centripetal_acceleration.jpg

2. Rotation vs Revolution • Rotation occurs when an object rotates around an internal axis • ex: the earth rotates around its axis (internal) every day • Revolution occurs when an object rotates around an external axis • ex: the earth revolves around the sun (external axis) every year

3. Rotational Speed • also called angular speed • equals the number of rotations per time unit • All parts of the earth rotate about its axis in the same amount of time…thus all parts of the earth have the same rotation …or the same number of rotations per time (revolutions per minute or RPM) When a twirling ice skater extends her arms outward, her rotational speed decreases.

4. Tangential Velocity • While the speed of the object is constant, its velocity is changing. Velocity vector and position vector for an object executing uniform circular motion

5. Tangential Speed • Tangential speed is directly proportional to rotational speed and the distance from the axis Tangential ~ Radial x Rotational Speed distance Speed -at the center of the earth…there is no tangential speed, (zero distance) but there is rotational speed

6. What type of speed is changing – rotational or tangential? twice as fast fast

7. Mathematical Relationship between tangential and rotational speed v = r  v = tangential speed r = radial distance  = rotational speed

8. Accelerometer • The deflection of the flame will be in the direction of the acceleration. This is because the hot gases of the flame are less massive and thus have less inertia than the cooler gases which surround

9. Centripetal Force Fc = mv2 / r • the force required to change the direction of a moving object http://webpages.uah.edu/~wilderd/resources.html http://www2.ignatius.edu/faculty/decarlo/Centripetal%20force.htm

10. Centripetal Force • center–seeking or toward the center • any force that causes an object to follow a circular path • think about the force you feel when riding a fast circular ride at an amusement park…without that force you would continue to move in a straight line…being “launched” form the ride

11. Centripetal Force As a car makes a turn, the force of friction acting upon the turned wheels of the car provide the centripetal force required for circular motion. As a bucket of water is tied to a string and spun in a circle, the force of tension acting upon the bucket provides the centripetal force required for circular motion. As the moon orbits the Earth, the force of gravity acting upon the moon provides the centripetal force required for circular motion.

12. Centrifugal Force…False Force • center-fleeing or away from the center • An apparent outward force that acts on a rotating object…it is due to inertia…an object’s desire to continue moving in a straight path. • The sensation of being thrown outward is attributable to the idea of inertia, rather than the idea of force.

13. Centrifugal force holds people on walls in Round Up ride

14. The Fictitious Force • When a ball swings on a string, many people would say that "CENTRIFUGAL FORCE" keeps the string taut. • There is actually no force pulling the ball out. • There is nothing out there pulling the ball! • All the sideways and back and forth forces you feel while riding in a car are FICTITIOUS, they are the results of your inertia resisting acceleration http://www.scigolf.com/scigolf/myths/myth2.htm

15. Tether Ball • Twirl a ball, at a constant speed, at the end of a rope. change of direction = acceleration http://www.hoopsplus.com/nss-folder/outdoorequipment/tether.jpg http://www2.ignatius.edu/faculty/decarlo/Centripetal%20force.htm

16. http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/circmot/rht.htmlhttp://www.glenbrook.k12.il.us/gbssci/phys/mmedia/circmot/rht.html

17. http://www.coolschool.ca/lor/PH12/unit4/U04L01.htm

18. Gravity: force of attraction between two objects. • Newton noted that the moon was falling toward the Earth. • The moon falls along a curved path. It acts as a projectile. • The moon has a component of velocity parallel to the Earth’s surface known as tangential velocity.

19. The force of gravitational attraction decreases as you move further from the center of the Earth. • The moon orbits the Earth, just as the Earth & other planets orbit the Sun. • The Sun is the center of the solar system.

20. Universal Gravitation • Law of Universal Gravitation: Every object attracts every other object with a force that for any two objects is directly proportional to the mass of each object.

21. Ocean Tides are due to the differences in the gravitational pull of the moon on opposite sides of the Earth. Variations in sun, moon and earth alignment causes low and high tides. • http://oceanlink.island.net/oinfo/tides/tides.html • http://home.hiwaay.net/~krcool/Astro/moon/moontides/

22. Spring & Neap Tides • the sun and moon are aligned, there are exceptionally strong gravitational forces, causing very high and very low tides. • The sun and moon are not aligned, the gravitational forces cancel each other out, and the tides are not as dramatically high and low.

23. Center of Gravity • Located at the object’s average position of weight (or balance point). • For a symmetrical object such as a ball. The CG is located in the center. • For an irregular shaped object (a bat), the CG is located towards the more massive end.

24. Toppling (falling over) • If the CG is located above the area of support, the object will not fall. If it is outside the support area, the object will fall over. • Neutral, Stable and Unstable Equilibrium.

25. Torque • The turning force used to turn a door knob or tighten a bolt produces torque. • Torque is defined as force times length of lever arm. For greatest torque, force should be applied perpendicular to the lever arm.

26. Torque = Force x distance • Notice that the unit of measurement for torque contains a distance (meter) and a force (Newton). • To calculate the torque needed to turn something, multiply the force by the distance from the center of the object you are trying to turn.