Unit 4 Vocabulary Terms Circular Motion Radius - R The radius is defined as half the diameter of a circle or the distance from the edge of a circle to its center. The radius is a unit of distance and can be measured in any unit of length. The symbol for the radius is “R” Period - T The period is defined as the amount of time required for one object to complete one revolution around another object. The common unit for the period is the second. The symbol for the period is “T”. e.g. The period for the earth to revolve around the sun is 365 days. e.g. A tether ball may complete one revolution around a pole in 3 seconds. Frequency - f The frequency is the number of revolutions or cycles occurring in one second of time. The symbol for frequency is “f ”. The common unit of frequency is cycles/sec also known as a Hertz (Hz). e.g. The tether ball can complete 1/3 of a revolution or cycle in one second. f= 0.333 Hz Relation of Frequency to the Period The frequency is related to the period by the following expression: Period = 1 / Frequency T = __1__ f Circular Velocity - Vc Remember that the velocity is equal to the change in displacement over the change in time. For a circle, we just replace displacement with circumference and time with the period. vc = 2πR circumference T period Centripetal Acceleration - ac The acceleration an object experience as it travels in a circle is called the centripetal acceleration. Although the object is traveling at a constant speed, its direction is continuously changing thus its velocity is also constantly changing. As a result, the object experiences an acceleration towards the center of the circle (centripetal). ac = v2 R Centripetal Force - Fc Centripetal force is the force resulting from a mass experiencing centripetal acceleration towards the center of a circle. Fc = mac Fc = m v2 R There is NO Centrifugal Force! When released, an object will not fly backwards from the center of the circle. Instead, the object will fly away tangentially from the edge of the circle. Centrifugal means “center fleeing”. This is common misconception in circular motion.