Ishmam Zaman-Static Friction

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Sacramento City College *

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410

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Mechanical Engineering

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Jan 9, 2024

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% W ¢y Experiment 6 Phys410 Friction Fall 2023 Introduction The force of friction is not a fundamental force of nature since it can be explained, at least in principle, in terms of the electromagnetic interaction between atoms. However, in many instances the frictional force can be described by simple empirical equations. In this experiment you will investigate the force of friction between a wooden blocksand the top of your lab table. The following empirical statements are sometimes made about friction. You should check each of these statements to see if they apply, or nearly apply, in your experiment. *The maximum static friction force is proportional to the normal force: Jsmax = ps N *For a given normal force, the frictional force is roughly independent of the area of contact between the surfaces. Setup You have been provided with a wood block. Note that portions of the block's surface have been removed to provide four different possible contact areas. 1. Choose a small flat region of the table that is nearly 2 meters from the edge of the table where your clamp is located. Make sure this region is clean. 2. Set up your equipment as suggested by the following sketch. the table by using a long string (measure its height above the table at two widely separated points). Method Maximum Static Friction Versus Normal Force for a Fixed Area of Contact 4. Start with a block without any added weights. Note that you can vary the force of contact between the block and the lab table (normal force, N) by placing weights on top of your block (don't forget to weigh your block too).
@ 5. Measure the maximum force that static friction can provide, fmax, for a given normal force by adding weights to the end of the string that hangs over the pulley until the block just starts to slide. Move the block slightly to ensure that it has not "stuck” to the table— but make sure that the block is absolutely stationary when you release it. Repeat with at least 10 normal forces and complete the attached data table. 6. Make a graph of fsmax On the vertical axis and N on the horizontal axis. Maximum Static Friction Versus Surface Area of Contact for a Fixed Normal Force 7. On your data sheet, make a sketch for each face of your block complete with dimensions—use a caliper to measure your block. 8. Set up your equipment as before. Place a fixed weight of intermediate size on your block to produce a fixed normal force. 9. Determine the maximum static friction for each face without changing the normal force. Maximum Tilt angle and the Coefficient of Static Friction 10. Estimate the static friction between your block and the top of your textbook as follows: +Place the block on top of your textbook and slowly raise one end of the textbook until the block begins to slide. «You can calculate the coefficient of static friction between your book and the block from the following equation Ms = tan(emax), where Omax is the maximum angle that the book makes with respect to the horizontal before the block begins to slide. Questions 1. What is the slope and intercept of your fomax versus N graph? Based on this graph, does it appear that the maximum frictional force proportional to the normal force? Explain. 2. Based on your fsmax versus N graph, what is the coefficient of static friction, 15, between your block and the top of the table? What are the dimensions of p5? 3. Do your data prove that the frictional force is not proportional to the area of contact!? Do you feel that your data are good enough to show that the frictional force has no significant dependence on area (within the limitations of your measurements)? Please explain. IHint: If y is proportional to , theny will double when you double z. Does the maximum static friction appear to double when the area of contact is doubled?
Partners I(ré/flf;z,q.} W Friction Data Sheet Name MMW\ 3 Maximum Static Friction Versus Normal Force for a Fixed Area of Contact M (grams) m (grams) | N = Mg (newtons) | fsmax = Mg (newtons) Wyl (09| 2.Yly/- 0.837 VLTI 15030 339472 .22G vYE.ugl 1760 4 (.7 M72 1. 71§ s e 13004 T,10477 7.2730 L. ua200.0 9] [.13%/L 2. 7Y Y64 | 220,091 F.31477 3. (30 846,44 | Y00.0 9 §. L% 1,41 196y 9 [ vy7. 04 4.27Y477 Y. LLoL Y6 14| 446.04 1025 y7L y. 451 \I1b.y 41 54¢.04 123472 G.753 Maximum Static Friction Versus Surface Area of Contact for a Fixed Normal Force vy L , l{ m (grams) | fomax (newtons) | A (contact area in cm? from sketch) [ 17%.0 9| ITIS 70,088 W 172.081 1017 36.%64 s 135.00 | 1.727 17. 7b Y[ 102.09 109916 7. \4b Maximum Tilt angle and the Coefficient of Static Friction Bmax = ,] li (; ! i /Ls=tan(0max)=’___D'22‘é1 Y44 o O / Z o ‘W W @ 0 V5 i | - § " t_{ A § % 5 iN ‘\ \f( ; 2‘ "‘is 1 :k—i\\ E 7 1| 1 1% om, ) ~ LA M G0 tm 0 Sketch the dimensions of the contact suléf'gcg for ea%}i‘%ace of the b}'ocfcm { A 01 em
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