University:
Felician University
Course:
PHYS-355 | Advanced Topics in Physics
Academic year:

2022
Views:

201

Pages:

13
Author:

larbiwxcvbn

Centrifugal Force in a Rotating Reference Frame From the reference frame of the ladybug inside the whirling can, the ladybug is being held to the bottom of the can by a force that is directed away from the center of circular motion. Centrifugal Force in a Rotating Reference Frame From a stationary frame of reference outside the whirling can, we see there is no centrifugal force acting on the ladybug inside the whirling can. However, we do see centripetal force acting on the can, producing circular motion. Centrifugal Force in a Rotating Reference Frame Nature seen from the reference frame of the rotating system is different. In the rotating frame of reference of the whirling can, both centripetal force (supplied by the can) and centrifugal force act on the ladybug. Centrifugal Force in a Rotating Reference Frame The centrifugal force appears as a force in its own right, as real as the pull of gravity. However, there is a fundamental difference between the gravity-like centrifugal force and actual gravitational force. Gravitational force is always an interaction between one mass and another. The gravity we feel is due to the interaction between our mass and the mass of Earth. Centrifugal Force in a Rotating Reference Frame In a rotating reference frame the centrifugal force has no agent such as mass—there is no interaction counterpart. For this reason, physicists refer to centrifugal force as a fictitious force, unlike gravitational, electromagnetic, and nuclear forces. Nevertheless, to observers who are in a rotating system, centrifugal force is very real. Just as gravity is ever present at Earth’s surface, centrifugal force is ever present within a rotating system. Centrifugal Force in a Rotating Reference Frame think! A heavy iron ball is attached by a spring to a rotating platform, as shown in the sketch. Two observers, one in the rotating frame and one on the ground at rest, observe its motion. Which observer sees the ball being pulled outward, stretching the spring? Which observer sees the spring pulling the ball into circular motion? Centrifugal Force in a Rotating Reference Frame think! A heavy iron ball is attached by a spring to a rotating platform, as shown in the sketch. Two observers, one in the rotating frame and one on the ground at rest, observe its motion. Which observer sees the ball being pulled outward, stretching the spring? Which observer sees the spring pulling the ball into circular motion? Answer: The observer in the reference frame of the rotating platform states that centrifugal force pulls radially outward on the ball, which stretches the spring. The observer in the rest frame states that centripetal force supplied by the stretched spring pulls the ball into circular motion. (Only the observer in the rest frame can identify an action-reaction pair of forces; where action is spring-on-ball, reaction is ball-on-spring. The rotating observer can’t identify a reaction counterpart to the centrifugal force because there isn’t any.) Centrifugal Force in a Rotating Reference Frame Why is centrifugal force not considered a true force? Assessment Questions 1. Whereas a rotation takes place about an axis that is internal, a revolution takes place about an axis that is a. external. b. at the center of gravity. c. at the center of mass. d. either internal or external. Answer: A Assessment Questions 2. When you roll a tapered cup across a table, the path of the cup curves because the wider end rolls a. slower. b. at the same speed as the narrow part. c. faster. d. in an unexplained way. Answer: C Assessment Questions 3. When you whirl a tin can in a horizontal circle overhead, the force that holds the can in the path acts a. in an inward direction. b. in an outward direction. c. in either an inward or outward direction. d. parallel to the force of gravity. Answer: A Assessment Questions 4. When you whirl a tin can in a horizontal circle overhead, the force that the can exerts on the string acts a. in an inward direction. b. in an outward direction. c. in either an inward or outward direction. d. parallel to the force of gravity. Answer: B Assessment Questions 5. A bug inside a can whirled in a circle feels a force of the can on its feet. This force acts a. in an inward direction. b. in an outward direction. c. in either an inward or outward direction. d. parallel to the force of gravity. Answer: A