Summary - Lab 6 - Static and Kinetic Friction PDF

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Summary (including processes used, math and formulas, and question responses) for Physics I Lab 6 - Static and Kinetic Friction. I am the author of this document. It is my own original work. All of my lab summaries received a perfect score from the professor....

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Tucker Knutson Lab 6 - Static and Kinetic Friction Physics I – Saint Paul College 10-27-2011 Purpose In this experiment, our goal is to analyze static and kinetic friction on a wooden block using a Force Sensor and a Motion Detector. We will measure the coefficients of static and kinetic friction of a wooden block sliding along a table, and we will determine whether friction is weight dependent. Preliminary Questions 1) The force required to start the box moving is greater than the force required to keep the box moving. This is based on the fact that the kinetic friction coefficient for an object is lower than the static friction coefficient. 2) The force of friction increases with increased weight because Ff=uf(FN) and FN=m(g) Procedure We began by attaching a Dual-Range Force Sensor to a block of wood via tape. A string was fixed to the force sensor’s pull-rod and the block + sensor was weighed on a scale (0.15 kg). A 1 kg mass was placed on top of the block and stabilized with tape. Part I Logger Pro was opened and we set a zero point (no tension on string). After our zero point had been set, we practiced our trial by pulling gently on the string with increased pulling force until the block began to slide. This is the practice we used in the following trials. We began collecting data and created a screen capture of the force vs time graph (see Data). Part II Mass was removed from the block, returning the mass of the block + sensors to 0.15 kg. We began data collection and performed the same motion of gentle pulling until sliding occurred. This was done three times. We repeated this practice four more times, adding 0.25 kg of mass each time. The peak static friction and kinetic friction values were averaged for each mass amount and recorded in a table with the corresponding normal force values (see Data). Part III This part of the experiment measured the coefficient of kinetic friction using a motion detector. We removed the force sensor from the block of wood and placed the block about 1.5 m away from a Motion Detector. We practiced our trials by sliding the block towards the motion detector so that it came to a stop about 0.5 m away from the detector. We collected five trials for the block by itself in this manner. We then added a 0.5 kg mass to the block and did five more trials. To obtain more accurate data, we created side rails for the latter five trials of Part III using two meter sticks (see Error Analysis).

Data Part I - Block Alone

Part II – Block + 500 g

Part III – Block Alone

Part III – Block + 500 g

Free Body Diagram

Calculations (Part III, Coefficients of Kinetic Friction)

Normal Force vs Peak Static Friction

Normal Force vs Kinetic Friction

Analysis 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11)

See Data The answer is correct. The coefficient of static friction is greater than the coefficient of kinetic friction. See Data See Data. Slope = 0.39. The line should indeed pass through the origin. See Data. Slope = 0.25. The line should indeed pass through the origin. See Data See Data No, because once the block is moving, the coefficient of kinetic friction remains constant regardless of velocity. Yes, Fk = ma No, uk=ma/mg and the m’s cancel out.

Error Analysis 1) The biggest error we observed during this lab was in Part III. When we were running the block alone trials, we found it very difficult to get accurate and consistent results. We concluded that the improper data was due to the block rotating as it slid towards the motion detector. To eliminate this error, we created side rails using two meter sticks taped to the table. This allowed the block to slide towards the detector without rotating. When we utilized this improvement in the block + 500 g portion of Part III, we got much more consistent results. 2) In Part II, our coefficient of kinetic friction equaled our slope. The kinetic friction from Part II was 0.25 In Part III, we determined our coefficient of kinetic friction to be 0.26 based on our improved, side rail trials for the block + 500 g. % error = (Part II uk – Part III uk) / Part II uk * 100

% error = 4 % Conclusion The result of this lab gave us a solid understanding of the relationships between, mass, weight, static and kinetic friction, acceleration, and applied force. It was interesting to see what effect increased mass had on the force of friction: it was enlightening to watch the force of friction increase with increased mass but not the coefficient of friction. We felt accomplished when we discovered a better method with which to undergo Part III....