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Physics C Dupre ´ Circular Motion

Physics C Dupre ´ Circular Motion. 1. Click anywhere in the black area below to see a movie. Circular Motion. B. C. A. A ball is going around in a circle attached to a string. If the string breaks at the instant shown, which path will the ball follow?. 2. Circular Motion. B. C.

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Physics C Dupre ´ Circular Motion

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  1. PhysicsC Dupre´Circular Motion 1

  2. Click anywhere in the black area below to see a movie.

  3. Circular Motion B C A A ball is going around in a circle attached to a string. If the string breaks at the instant shown, which path will the ball follow? 2

  4. Circular Motion B C A A planet is going in a circular orbit around a star. If the star was to suddenly disappear at the instant shown, which path will the planet follow? 2

  5. Circular Motion B C A A ball is going around in a horizontal circle on a frictionless table attached to a string. If the string breaks at the instant shown, which path will the ball follow? 2

  6. N v T mg Uniform Circular motion Uniform circular motion in a horizontal plane mw= mass (downward) N = mg r m Net force = T F = ma T = m (v2 / r) mw T = mwg as it is at rest. mwg = m v2 / r

  7. N v T r m mg mw Uniform Circular motion Uniform circular motion in a horizontalplane T = m (v2 / r) What is the physical meaning of the formula? • What happens if the initial speed v of the bob is forced to move faster? • A greater T is needed, the greater mw, to keep the radius of motion r.It will slide out to attain a greater r. • What happens if there is energy lost due to friction on the plane? • v decreases  By T = mv2 / r, r decreases • What happen if an additional mass is added to the weight mw? • M moves down  r decreases and T increases  v increases

  8. N v T r m mg M Uniform Circular motion Uniform circular motion in a horizontal plane T = m (v2 / r) What is the physical meaning of the formula? • (4) What happens if the string suddenly break? • Tension suddenly disappears and there is no more centripetal force. • No more circular motion can be maintained. • The bob will move with its velocity tangent to the circle • at the instant the string breaks

  9. Circular Motion Review • When we see an object carrying out circular motion, we know that there must be force acting on the object, directed towards the center of the circle. • When you look at the circular motion of a ball attached to a string, the force is provided by the tension in the string. • When the force responsible for the circular motion disappears, e.g. by cutting the string, the motion will become linear.

  10. Circular Motion Review 2 • In most cases, the string force not only has to provide the force required for circular motion, but also the force required to balance the gravitational force. • Important consequences: • You can never swing an object with the string aligned with the horizontal plane. • When the speed increases, the acceleration increases up to the point that the force required for circular motion exceeds the maximum force that can be provided by the string.

  11. Circular Motion and its Connection to Friction • When you drive your car around a corner you carry out circular motion. • In order to be able to carry out this type of motion, there must be a force present that provides the required acceleration towards the center of the circle. • This required force is provided by the friction force between the tires and the road. • But remember ….. The friction force has a maximum value, and there is a maximum speed with which you can make the turn. Required force = Mv2/r. If v increases, the friction force must increase and/or the radius must increase.

  12. Consider the following situation: You are driving a car with constant speed around a horizontal circular track. Normal On a piece of paper, draw a Free Body Diagram (FBD) for the car. How many forces are acting on the car? A) 1 B) 2 C) 3 D) 4 E) 5 Friction Gravity The net force on the car is A. Zero B. Pointing radially inward (centripetal!)C. Pointing radially outward(centrifugal?) 25

  13. Question 3 • Davain sits on the outer rim of a merry-go-round, and Diego sits midway between the center and the rim. The merry-go-round makes one complete revolution every two seconds. • Diego’s angular velocity is: Diego Davian (a)the same as Davian’s (b)twice Davian’s (c)half Davian’s

  14. Summary • Uniform Circular Motion • Speed is constant • Direction is changing • Acceleration toward center a = v2 / r • Newton’s Second Law F = ma

  15. Click on this question to investigate! How does this apply to planets? Check out this tutorial! http://www.physicsclassroom.com/ Are you HYPER enough to learn and link? http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

  16. Check out this site for simulations of circular motion And so many other simulations! http://www.animations.physics.unsw.edu.au/mechanics/chapter3_circularmotion.html

  17. Citations Graphics: Slides 9, 10, 11 Physics Text 1 Chapter 3 Vectors and Two-Dimensional Motion Slides 12, 13 Physics Text 2 Video: Planetary Orbits are Elliptical. Discovery Channel School. 2005.Discovery Education. 17 July 2009http://streaming.discoveryeducation.com/ Websites: http://hyperphysics.phy-astr.gsu.edu/hbase/orbv.html#co http://www.physicsclassroom.com/ http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html http://www.animations.physics.unsw.edu.au/mechanics/chapter3_circularmotion.html

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