Centrifugal Force

| Introduction to | Circular Motion | | Physics | | | HomeNewton 's LawsMomentum & ImpulseProjectile Motion & Mechanical EnergyCircular MotionLinks & Extras | IntroductionIn uniform circular motion the magnitude of the velocity of the object in motion remains constant. For example at car turning around a circular curve will stay at 12 m/s throughout the entire turn (provided the driver does not brake). The direction of the velocity vector is changing. A force is required in uniform circular motion.Centripetal Force & AccelerationSince an object in motion will travel in a straight line (Newton 's First Law) an force must be required to accelerate the mass . This force does not cause a change in velocity as stated in the introduction, but rather it is responsible for the change in direction. The centripetal acceleration (ac) is equal to the square of the velocity (v) over the radius of the circular motion. According to Newton 's Second Law, then the centripetal force (Fc) should be the mass of the object (m) times the centripetal acceleration. The equations are pictured above.Important Facts * "Centrifugal" force is a fictitious force. It is a perceived force. There is no reactive force as per Newton 's Third Law. This the 'force ' that you feel when you take a turn in a car or on a roller coaster. If this was a real force, then when your car slips on ice or the roller coaster your on breaks, you should fly outward perpendicular to the direction of your motion. Obviously this is not true. * If the centripetal force is removed, the object will continue on a path tangent to the circle. In other words, you should continue in a straight line in the same direction at the motion at the exact instant the centripetal force is removed. * The centripetal force vector always points to the center of the circlar motion. * The centripetal could be the tension in a string, gravity (for simple planetary orbit like in simulation), friction (i.e. the car on pavement), or other force. This equivalency is very helpful for our calculations. See table below: Force | Equation | Info | Tension | | Like a string or other physical connection. i.e. Swinging keys on a lanyard. The keys are the mass and the Fc is equal to the tension in the lanyard. | Gravity | | Gravity keeps items planets and moons in orbit (a simple form of uniform circ. motion). There is not physical connection. See Newton 's Law of Universal Graivitation | Friction | | Friction is the only thing keeping cars from spinning out at every turn. In icy conditions there is little friction and so you have to keep your speed low or else you will spin out of your turns. |
An Example
Why does the roller coaster stay up?The roller coaster stays up because the centripetal force is greater than or equal to the weight of the car and the people. Both the weight and Fc vectors are pointed downward at the top. However the reaction force or normal force (Fn) is upward and equal to Fc. The inertia (urge for to travel in a straight line) of the car pushes it up (Fn) against the track with a force equal to Fc. So: Fnet = mg - Fn. The people may feel a feeling weightlessness if Fnet is 0. |

Links: & Extras | IntroductionIn uniform circular motion the magnitude of the velocity of the object in motion remains constant. For example at car turning around a circular curve will stay at 12 m/s throughout the entire turn (provided the driver does not brake). The direction of the velocity vector is changing. A force is required in uniform circular motion.Centripetal Force & AccelerationSince an object in motion will travel in a straight line (Newton 's First Law) an force must be required to accelerate the mass . This force does not cause a change in velocity as stated in the introduction, but rather it is responsible for the change in direction. The centripetal acceleration (ac) is equal to the square of the velocity (v) over the radius of the circular motion. According to Newton 's Second Law, then the centripetal force (Fc) should be the mass of the object (m) times the centripetal acceleration. The equations are pictured above.Important Facts * "Centrifugal" force is a fictitious force. It is a perceived force. There is no reactive force as per Newton 's Third Law. This the 'force ' that you feel when you take a turn in a car or on a roller coaster. If this was a real force, then when your car slips on ice or the roller coaster your on breaks, you should fly outward perpendicular to the direction of your motion. Obviously this is not true. * If the centripetal force is removed, the object will continue on a path tangent to the circle. In other words, you should continue in a straight line in the same direction at the motion at the exact instant the centripetal force is removed. * The centripetal force vector always points to the center of the circlar motion. * The centripetal could be the tension in a string, gravity (for simple planetary orbit like in simulation), friction (i.e. the car on pavement), or other force. This equivalency is very helpful for our calculations. See table below: Force | Equation | Info | Tension | | Like a string or other physical connection. i.e. Swinging keys on a lanyard. The keys are the mass and the Fc is equal to the tension in the lanyard. | Gravity | | Gravity keeps items planets and moons in orbit (a simple form of uniform circ. motion). There is not physical connection. See Newton 's Law of Universal Graivitation | Friction | | Friction is the only thing keeping cars from spinning out at every turn. In icy conditions there is little friction and so you have to keep your speed low or else you will spin out of your turns. | An Example Why does the roller coaster stay up?The roller coaster stays up because the centripetal force is greater than or equal to the weight of the car and the people. Both the weight and Fc vectors are pointed downward at the top. However the reaction force or normal force (Fn) is upward and equal to Fc. The inertia (urge for to travel in a straight line) of the car pushes it up (Fn) against the track with a force equal to Fc. So: Fnet = mg - Fn. The people may feel a feeling weightlessness if Fnet is 0. |