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# Download Section 7: Centripetal Acceleration Misconceptions

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Transcript

Section 7: Centripetal Acceleration Misconceptions Student view Centripetal force is a force. If a force is applied perpendicularly to an objects velocity, it will start moving in that direction When an object traveling in a circle, has a constant speed, its velocity is not changing and therefore cannot be accelerating. If a car makes a sharper turn, the radius is larger. Physicist’s view Centripetal force is any force that causes uniform circular motion. Centripetal force is caused by many types forces - gravitational force causes the Earth to go around the Sun, electrical force causes electrons to be attracted to the nucleus, frictional forces cause cars to make turns on the highway, and tension in a sting makes a toy car move in a circle. If a constant force is applied perpendicularly to an objects velocity, the result will be uniform circular motion. But if the force is extremely large it will not be noticed as a curved path because the change in velocity will be so great that it will appear to now be moving nearly in the direction of the applied perpendicular force. Since velocity is a vector quantity, an object that is traveling in a circle is constantly changing its direction and is constantly accelerating. And if the change is constant as in uniform circular motion (constant speed), its acceleration is constant. When you draw the diagram of the turn and draw the radius of the turn, it can be seen that a tight turn (e.g. a sharper turn) has a small radius. In order to keep an object moving at a constant speed, a force must be applied. When rounding a curve, a force pushes you away from the center of the curve and into the door on the outside of the curve = a centrifugal force. Newton’s First Law of Motion states that an object in motion remains in motion and an object at rest remains at rest unless acted upon by an unbalanced force. This misconception arises from student experiences that objects slow down and stop in the real world due to friction. In the next chapter there will be many examples of objects with extremely low friction that continue to move until an unbalanced force is applied. The unbalanced force is the centripetal force toward the center of the curve caused by either the friction from the seat or the seat belt or the inside of the door. What is happening is the passenger in the car is traveling in a straight line while the car makes a turn. The passenger travels in a straight line and the car door turns into the passenger. Since students have not discussed inertia and Newton’s First Law of Motion this is a topic for the next chapter.