1. Brain Teaser I wish tomorrow was yesterday so today would be Friday. What day is it?

2. Circular Motion Ms. Bartlett December 7-8, 2015

3. Circular Motion Centripetal Acceleration Centripetal – center seeking; toward the center centripetal acceleration (ac) – acceleration toward the center of circular motion. The formula for centripetal acceleration is: where v is the tangential velocity and r is the radius of the circle uniform circular motion – the movement of an object at a constant speed around a circle with a fixed radius.

4. Centripetal Acceleration One way of measuring the speed of an object moving in a circle is to measure its period, T, the time needed for the object to make one complete revolution. The frequency, f, is how many revolutions per second. T = 1/f(period is the reciprocal of frequency) During this time, the object travels a distance equal to the circumference of the circle, 2πr. The object’s speed, then, is represented by v = 2πr/T. v = distance = 2πr time T

5. Centripetal Acceleration Since and v = 2πr T then

6. Centripetal Acceleration Because the acceleration of an object moving in a circle is always in the direction of the net force acting on it, there must be a net force toward the center of the circle. This force can be provided by any number of agents. When a hammer thrower swings the hammer, as in the adjoining figure, the force is the tension in the chain attached to the massive ball.

7. Circular Motion When an object moves in a circle, the net force toward the center of the circle is called the centripetal force. To analyze centripetal acceleration situations accurately, you must identify the agent of the force that causes the acceleration (such as tension on a string). Then you can apply Newton’s second law for the component in the direction of the acceleration in the following way. Newton’s Second Law for Circular Motion F = m a The net centripetal force on an object moving in a circle is equal to the object’s mass times the centripetal acceleration.

8. Circular Acceleration r is the radius of the circle v is the tangential velocity a (or a c ) is the centripetal acceleration F c is the centripetal force

9. A Nonexistent Force According to Newton’s first law, you will continue moving with the same velocity unless there is a net force acting on you. The passenger in the car would continue to move straight ahead if it were not for the force of the door acting in the direction of the acceleration. The so-called centrifugal force, or apparent outward force, is a fictitious, nonexistent force. Centrifugal – center fleeing; away from the center.

10. Circular Motion Review Formulas: F c = m a c = mv 2 r a c = v 2 = 4π 2 r r T 2 T is the period (time for one revolution around the circle.) The distance around the circle is 2  r. Uniform circular motion has constant speed and constant radius. The net force toward the center of the circle causes the centripetal acceleration.

11. HOMEWORK Finish the Kinematics Packet. Next time we will work exclusively with circular motion problems. You will have a projectile & circular motion test on Fri/Mon.