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MMB LAB 2 - lab report regarding sliding friction got a good mark but be sure to use and

lab report regarding sliding friction got a good mark but be sure to u...

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Engineering mechanics (MMB 241)

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University of Botswana

Academic year: 2021/2022

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Lungile Balise

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NAME; LUNGILE MIA BALISE

ID NUMBER; 202003097

MMB 241; DYNAMICS OF A PARTICLE

REPORT TITLE; SLIDING FRICTION

SUMBITION DATE; 13 APRIL 2022

1. INTRODUCTION..................................................................................................................

1 AIMS AND OBJECTIVES............................................................................................

1 BACKGROUND/THEORY...........................................................................................

1. INTRODUCTION..................................................................................................................
- 1 AIMS AND OBJECTIVES............................................................................................
- 1 BACKGROUND/THEORY...........................................................................................
- 1 APPARATUS USED.......................................................................................................
- 1 PROCEDURE.................................................................................................................
1. RESULTS................................................................................................................................
1. DISCUSSION..........................................................................................................................
1. CONCLUSION.......................................................................................................................
1. REFERENCES.......................................................................................................................
1. APPENDIX.............................................................................................................................

force it experiences. Using x and y coordinates the forces can be resolved into 2 equations to find the normal force and frictional force.

∑ Fy = N− mgcosθ = 0

N = mgcosθ

Σ Fx = mgsinθ – fk = max

Where fk = μkN

For both the kinetic friction force and static friction force there is a constant (in the case of the above diagram the kinetic friction (μk) is the ratio between the kinetic frictional force (Fk) and the normal force (N) but is applied the same for static friction. Figure 1 is used an illustration to describe the forces, the experiment was done on a flat surface thus weight acts directly vertically.

1 APPARATUS USED.......................................................................................................

The apparatus used include a work panel, friction plate of different materials i. metal, wood and plastic, a friction sled, weight hanger and weights. All of these materials are instrumental to attain an accurate coefficient of friction of the different materials.

Figure 2: the experimental setup for analysis of static and kinetic co efficient of friction

1 PROCEDURE.................................................................................................................

Figure 3; setup for weighing the sled

Friction sled

Weight hanger

Work panel

To start the experiment the friction sled should be weighed as in the setup in figure 3 making sure that the sled balances with the weights added to the weight hanger. After weighing the sled, a metal friction plate was attached to the sled which was put on the work panel as setup in figure 2 with the plane angle set to zero. A string was then attached to sled which went through the pulley to weight hanger, without tapping the work panel weights were slowly added to the weight hanger until the pulling force overcame the static friction. This was done again this time with 80g (evenly distributed to give 2*40g stacks) added to the sled, the static friction results were recorded and the experiment was done again each time adding more weights(according to the result table) to the sled ,this was repeated with wood-wood surfaces and plastic-plastic surfaces. To get the kinetic friction the same process was repeated but before adding weights to the weight hanger the work panel was tapped to reduce/remove static friction.

2. RESULTS................................................................................................................................

0 2 3 3 4 5.

f(x) = 0 x + 0.

f(x) = 0 x + 0.

SLIDING FRICTION FOR A METAL-METAL SURFACE

staticpulling weight

FORCE DUE TO SLED WEIGHT (N)

PULLING FORCE (N)

Graph 1; depicts sliding friction and both kinetic and static friction along the with their coefficients of friction of a metal-metal surface

As for graph 3, the kinetic friction is steeper than the static which indicates an error occurred. Some of the errors that contribute to the inaccurate results include adding weights to observe acceleration of the sled rather than the weight it took to make initial movement i. to overcome static friction. This happens because what is observed as constant motion is often acceleration of the sled moreover the lack of smaller weights e. 5g, 2g weights affected the results as the margin for error become greater. Along with these, another problem encountered during experiment was accurately weighing the empty sled, the work panel was an obstruction as it constantly came in contact with sled which affected the balancing weight. To get an accurate value the weighing process had to be done more than twice which was very time consuming.

From the experiment conducted, the weight is one of the most important contributing factors to the amount of frictional force as object has and since on a flat surface it is equal to the normal force, this weight which is depicted as the pulling weight can be used to compare the roughness/smoothness of a surface. from the graphs, specifically graph 3 the final weight is considerably smaller than the others and so was the highest pulling force at 0 while graph 1 for a metal-metal surface the highest sled weight was high thus the pulling force was also high with the final pulling force being 1 this trend suggests that the surfaces were a bit slippery/smooth. On the other hand the pulling force of wood was very high at 1 despite its highest weight being very similar to that of plastic at 4, this shows that wood was the roughest surface among them.

The gradient (μs) can also be used to draw conclusion of which surface was the roughest with 0 indicating a very slippery surface and 1 a very rough surface. Using this, the wood-wood surface is the roughest followed by the plastic-plastic surface then the metal-metal surface.

According to the guidance notes most if not all the coefficients of both static and kinetic friction are equal or less than 0 for the surfaces that the experiment was conducted on. These results are in line with the experiment outcomes as for all surfaces as shown in the graphs above none of the gradients are above 0, with the highest being static coefficient of wood at 0 which indicates that the experimental results are very accurate.

3. CONCLUSION.......................................................................................................................

The experiment was successful in that, the coefficients of kinetic and static friction were calculated and the obtained results were different with each surface thus an accurate comparison and analysis on how surfaces and weight affect friction was made. From this, the final and vital results of the experiment in are summarized in the tabular form below.

material Coefficient of static friction obtained

Coefficient of kinetic friction obtained Metal-metal 0 0. Wood-wood 0 0. Plastic-plastic 0 0.

4. REFERENCES.......................................................................................................................

Gratton, L. M., & Defrancesco, S. (2006). A simple measurement of sliding friction coefficient. IOP Punblishing Ltd, 3-4.

Empty weight of sled; 149g Sled weight added(g)

Total weight incl. Empty sled (g)

Total force in sled (W) (N)

Pulling weight(g)

Pulling force(N)

0 149 1 50 0.

80 (4 229 2 70 0.

160 (4 309 3 80 0.

240 ( 4 389 3 110 1.

320 ( 4 469 4 130 1.

Table 5: the static friction on a plastic-plastic surface

Empty weight of sled; 155g Sled weight added(g)

Total weight incl. Empty sled (g)

Total force in sled (W) (N)

Pulling weight(g)

Pulling force(N)

0 155 1 40 0.

80 (4 235 2 60 0.

160 (4 315 3 70 0.

240 ( 4 395 3 80 0.

320 ( 4 475 4 100 0.

Table 6: the kinetic friction on a plastic-plastic surface

Empty weight of sled; 155g Sled weight added(g)

Total weight incl. Empty sled (g)

Total force in sled (W) (N)

Pulling weight(g)

Pulling force(N)

0 155 1 30 0.

80 (4 235 2 40 0.

160 (4 315 3 60 0.

240 ( 4 395 3 80 0.

320 ( 4 475 4 90 0.

Multiple Choice

Multiple Choice

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