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Centrifugal Force: The Fictitious Force Daniel J. Reichard

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Definition Commonly known to be the outward force on an object away from the center of rotation – Examples: Water staying in a bucket when it is quickly flipped upside down An object moving to the right side of a car when making a sharp left turn Amusement park ride where passengers are stuck to the walls as they spin rapidly However, this force does not actually exist

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Why, then, does water stay in the bucket? Why does an object move to the right when a car turns to the left? Why does a person stick to the side of rapidly spinning ride? The explanation for this phenomenon is simple and does not involve a centrifugal force!

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Connection: Circular Motion In order for an object to move in a circular path, there must be an external force, according to Newton’s first law of motion (law of inertia). This force must be in the direction of the object’s acceleration (towards the center), according to Newton’s second law of motion. This force is called the centripetal force.

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FcFc FcFc FcFc FcFc FcFc FcFc FcFc FcFc vtvt vtvt vtvt vtvt vtvt vtvt vtvt vtvt F c = centripetal force V t = tangential velocity Centripetal Force According to Newton’s law of inertia, an object in motion will stay in motion with the same speed and same direction unless it is acted on by an external force. Therefore, an object in circular motion wants to continue moving in the direction tangential to the circular path. However, a centripetal force pulls the object perpendicularly to the object’s velocity. This creates a circular path.

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Explanation of Water Bucket Example Why, then, does water stay in the bucket? When a bucket of water rotates in a vertical circular path, the water appears to be stuck to the bucket. The water wants to continue moving at a velocity tangential to the circular path (v t ). The sides of the closed bucket prevent the water from doing so. Therefore, the water is forced to move in the same path as the bucket. There is no force pushing the water away for the center (no centrifugal force). Instead, the bucket is pushing the water toward the center of rotation.

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Explanation of Car Example The object in the car wants to continue to move in a straight line even though the car is turning. The object initially does continue to move in a straight line, but it eventually is stopped by the right side of the car. As the car continues to move in a circular path, the object remains against the right side of the car, just like the water in the bucket. Once again, there is no centrifugal force acting on the object. Instead, the side of the car is pushing the object in a circular path.

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Explanation of Spinning Ride Example Like the other two examples, the object, in this case a person, wants to continue moving in a straight line due to inertia. However, the walls of the spinning ride do not allow the person’s body to move in a straight line. Therefore, the person becomes “stuck” to the wall even though there is no force pushing the person against the wall.

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Conclusion In conclusion, there is no such thing as a centrifugal force. Circular motion of any kind can be explained using the law of inertia and centripetal force. There is no force that pushes an object away from the center of its rotation. The reason the object moves in a circle is because it wants to continue to move in a straight line tangent to the circular path.

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New Insight After research on this topic, I gained a lot of information on how and why objects move in a circular path. It is interesting that a centrifugal force is a common explanation for circular motion when it is not even true. I can now easily visualize what really happens in the real world with regards to inertia, centripetal force, and circular motion. This new information is beneficial when solving difficult circular motion problems.

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Works Cited http://regentsprep.org/regents/physics/phys0 6/bcentrif/centrif.htm http://regentsprep.org/regents/physics/phys0 6/bcentrif/centrif.htm http://csep10.phys.utk.edu/astr161/lect/histo ry/newton3laws.html http://csep10.phys.utk.edu/astr161/lect/histo ry/newton3laws.html http://en.wikipedia.org/wiki/Centrifugal_force

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