Mary Ta 5/26/11 Lab 5: Graph Matching Prof. Siamak Ghandian Lab 5: Static and Kinetic Friction OBJECTIVES: To use a dual range force sensor to measure the force of static friction and determine the relationship between force of static friction and weight of an object. To measure the coefficients of static and kinetic friction for a block and track using a motion detector to independently measure the coefficient of kinetic friction and compare it to the previously measured value. The final objective is to determine the coefficient of kinetic friction depends on weight. MATERIALS: Computer Vernier Computer Interface Logger Pro Vernier Motion Detector Vernier Force Sensor String Block of Wood with Hook Balance/Scale Mass Set PRELIMINARY QUESTIONS: 1. To push a box across a floor, the force needed to start the box moving is greater than the force necessary to keep the box moving. This is because the starting friction is greater than the kinetic friction. Once you have overcome the initial “threshold,” only the kinetic friction needs to be matched. 2. The force of friction is related to the weight of the box through the equation of f =µN. N is the Normal force that pushes up on the weight of the box because there is always an equal and opposite force on things. Therefore, the greater the weight of the box, the greater the Normal force pushing up onto the box which increases the friction necessary to overcome before the box will move. **All trial graphs will be added in order in the analysis section** PROCEDURE: PART I 1. After obtaining and setting up all the necessary materials, I began by measuring the mass of the block. I recorded this value in the provided data table. 2. I made sure the Dual-Range Force sensor was connected to Channel 1 of the interface and set the range switch to 50 N. 3. On Logger Pro, I opened the file “12a Static Kinetic Frict” from the Physics folder.
4. I tied two loops on a piece of string and connected these loops to the hooks on the force sensor and the wooden block. 5. Then I put the 1 kg. mass on top of the block and fastened them to the block to prevent the mass from falling or moving. 6. I practiced slowly pulling the string to the point where the block is just about to move but doesn’t yet. This is the point where our force matches the max force of the static friction. Then I gently pulled so the block began moving at a constant velocity across the table. This is when our force exceeds the static friction and is matching the kinetic friction. 7. I sketched a graph of the force vs. time for the force I just experimented with and labeled the portions of the graph when the block was at rest, when the block started to move, and the time when the block was moving at constant speed.
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