Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. In this Lab we are going to investigate the force of friction between two solids and we we are going to calculate the coeficients of static and kinetic (or sliding) friction between them.

Material needed :

1. Spring Scale.

2. Wooden block.

3. Flat plank of wood.

4. Drawing Protractor.

Before doing Lab Assignment 5, it is recommended that you study the following websites:

https://www.youtube.com/watch?v=fo_pmp5rtzo&ab_channel=CrashCourse

http://hyperphysics.phy-astr.gsu.edu/hbase/frict2.html

https://www.khanacademy.org/science/physics/forces-newtons-laws/inclined-planes-friction/a/what-is-friction

Now, you can go to Lab Assignment 5 and complete it.

1. Submit a picture of your Lab device.

2. submit a Lab report

EXPERIMENT . . . 5.2 Friction Kinetic or sliding friction Purpose Investigate friction and measure the coefficients of friction. MS Concept and Skill Check An object placed on an inclined plane may or may not slide. If the object is at rest, the force of friction is opposing the tendency of the object to slide down the plane. When the plane has been tilted at a certain angle 0 with the horizontal, the object begins to slide down the inclined plane. If the object slides down the inclined plane at a constant speed, then the force of friction F, is equal to the force down the plane Fi. The force down the plane is the same as the component of the object's weight parallel to the plane, as shown in the figure. The parallel component of weight is described by Fi = Fw sin 0, where w is the weight of the object. The perpendicular component of weight is described by FJ = Fw cos 0. When sliding just begins and the object is moving at a constant speed, the coefficient of friction u is given by F1 _ Fw sin 0 MK = FK H= F = FI Fw COS 0 = tan 0. Materials spring scale (with capacity sufficient to measure the weight of the object) object: book, chalkboard eraser, F 2-by-4 block, or similar object Incline flat board FW plane. string (1 m) masking tape protractor Procedure K. 1. Select an object and a flat board for this experiment. Describe the object and the surface of the Jeight board in Table 1. 2. Tape the string to the end of the object. Hang the object by the string from the spring scale. Measure the weight of the object. Record this value in Table 2. Block? 3. Place the flat board on a horizontal surface. Hold the spring scale and, with the string held parallel to the level board, pull the object along the board at a constant speed. With the spring scale, measure the amount of force required to keep the object moving at a uniform rate. FK . Repeat this procedure several times, average your results, and record this value in Table 2 as the force of sliding friction between the surface of the board and the surface of the object. 4. Detach the string from the object. Place the object on the flat board. Slowly lift one end of the board. Continue increasing the angle of the board with the horizontal until the object starts to slide. Use the protractor to measure this angle. Record the value of this angle in Table 3 as the angle for static friction. The tangent of this angle is the coefficient of static friction. FS. May LABORATORY MANUAL 29 Me-Tan &5. Move the object to one end of the board. Again, slowly lift this end of the board while your lab partner lightly taps the object. Adjust the angle of the board until the object slides at a constant speed after it has received an initial light tap. Use the protractor to measure this angle and record it in Table 3 as the angle for sliding friction. The tangent of this angle is the coefficient of sliding friction. 6. Repeat the experiment with a different object so that each lab partner has data to analyze. Observations and Data Table 1 Description Object Surface Table 2 Weight of object (N) 1 2 3 Average Force of sliding friction (N) Table 3 Motion Angle (degrees) ' u = tan 0 Static NS Sliding Analysis 1. From the data in Table 3, calculate the coefficients of static and sliding friction for the object used. Record these values in Table 3.2. Explain any difference between the values for the coefficients of static and sliding friction. 3. Using the data in Table 2, calculate the coefficient of sliding friction. Show your work. 4. Are your values for /sliding from Questions 1 and 3 equal? Explain any differences. 5. A brick is positioned first with its largest surface in contact with an inclined plane. The plane is tilted at an angle to the horizontal until the brick just begins to slide, and the angle, 0, of the plane with the horizontal is measured. Then the brick is turned on one of its narrow edges, the plane is tilted, and 0 is again measured. Predict whether there will be a difference in these measured angles. Explain your answer in terms of the equation for the force of friction. Is the coefficient of static friction affected by the area of contact between the surfaces? 6. A brick is placed on an inclined plane, which is tilted at an angle to the horizontal until the brick just begins to slide. The angle, 0, of the plane with respect to the horizontal is measured. Then the brick is wrapped in waxed paper and placed on a plane. The plane is tilted, and 0 is again measured. Predict whether there will be a difference in these measured angles. Explain.7. From your answers to the previous two questions, determine the factors that influence the force of friction. Application While looking for a set of new tires for your car, you find an advertisement that offers two brands of tires, brand X and brand Y, at the same price. Brand X has a coefficient of friction on dry pavement of 0.90 and on wet pavement of 0.15. Brand Y has a coefficient of friction on dry pavement of 0.88 and on wet pavement of 0.45. If you live in an area with high levels of precipitation, which tire would give you better service? Explain. Extension Using another object, measure its weight and the force necessary to pull it along a horizontal surface at a constant speed. Record the information in a data table similar to Table 2. Calculate the coefficient of sliding friction. Since / = tan 0, find the angle 0. Estimate the angle at which sliding at a constant speed would begin. Using this as your prediction, slowly raise the flat board while lightly tapping the object. Record the angle at which the object begins sliding at a constant speed. Compare your prediction to your experimental results