Static and Kinetic Friction

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static and Kinetic Friction If you try to slide a heavy box resting on the floor, you may find it difficult to get the box moving. Static friction is the force that is counters your force on the box... . If you apply a light horizontal push that does not move the box, the static friction force is also small and directly opposite to your push. If you push harder, the friction force increases to match the magnitude of your push. There is a limit to the magnitude of static friction, so eventually, you may be able to apply a force larger than the maximum static force, and the box will move. The maximum static friction force is sometimes referred to as starting friction. We model static friction, Fstatic, with the inequality Fstatic  s N where s is the coefficient of static friction and N the normal force exerted by a surface on the object. The normal force is defined as the perpendicular component of the force exerted by the surface. In this case, the normal force is equal to the weight of the object. Once the box starts to slide, you must continue to exert a force to keep the object moving, or friction will slow it to a stop. The friction acting on the box while it is moving is called kinetic friction. In order to slide the box with a constant velocity, a force equivalent to the force of kinetic friction must be applied. Kinetic friction is sometimes referred to as sliding friction. Both static and kinetic friction depend on the surfaces of the box and the floor, and on how hard the box and floor are pressed together. We model kinetic friction with Fkinetic = k N, where k is the coefficient of kinetic friction. In this experiment, you will use a Force Sensor to study static friction and kinetic friction on a wooden block. OBJECTIVES • Use a Dual-Range Force Sensor to measure the force of static friction. • Determine the relationship between force of static friction and the weight of an object. • Measure the coefficients of static and kinetic friction for a particular block and track. • Determine if the coefficient of kinetic friction depends on weight. MATERIALS computer string Vernier computer interface block of wood with hook Logger Pro balance or scale Vernier Force Sensor mass set SIMULATION ADDRESS 12 - 2 Physics with Vernier PRELIMINARY QUESTIONS 1. In pushing a heavy box across the floor, is the force you need to apply to start the box moving greater than, less than, or the same as the force needed to keep the box moving? On what are you basing your choice? 2. How do you think the force of friction is related to the weight of the box? Explain. PROCEDURE Part I Starting Friction 1. Before clicking begin, read the description of the activity. Once the object begins moving, what do we know about its velocity? 2. Once you click begin, the simulation shows a block connected by a string to a force sensor. The screen of the sensor’s interface is shown in the box on the top right. The type of object and the surface it rests on can be chosen in the top left [Show More]

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