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LAB FACTORS AFFECTING FRICTION Mr. Koenig Factors affecting friction. Concepts to Investigate: Friction equation, coefficient of static friction, coefficient of sliding friction (kinetic), independence of surface area and friction. FN Ffriction Fapplied m1 m1 m1g = Wt Friction is the force that opposes motion The minimum force needed to keep a body moving is equal to the friction force. That is, Fapplied = Ffriction, if velocity 0 & Acceleration = 0 Weight (Wt) is the downward force of gravity. If no other forces act on the object then Wt = FN, where FN is the upward force the surface exerts on the object. Materials Needed: Athletic shoe Set of masses Pasco force sensor Computer with Data Studio Koenig Physics 2014-15 Direction of motion (constant velocity) Fk and Fs Fapplied Force probe Computer w/ Data Data Studio Shoe USB link Procedure: To Open Data studio: plug USB connector into computer and a force probe to the USB link. Each time the Force probe is to be used you must click the start key on the computer and then the zero button on the Force probe, then you may use the probe to pull, push, or hang something. In order to calculate the weight of the friction shoe, first click the start key on the computer and then click the zero button on the force probe then hang the friction Shoe from it and hold as steady as possible. Attach a force probe to the Shoe. Press the start button on the computer to prepare it for data collection. While in the relaxed position, press the zero button, on the force probe- Pull horizontally until the Shoe JUST begins to move. Measure this value as the magnitude of static friction, (the force required to set the shoe sliding) Remember, pull gently and watch for when the Shoe just “Breaks Free”, record the force required to accomplish this. When the shoe has no additional mass in it you may have to do this several times to get an accurate average value. Use the digits display with the graph display. After the shoe begins to move measure the force required to keep it moving at a constant velocity. This is a measurement of the magnitude of the sliding friction force (kinetic). Repeat these procedures by completing the table below. Graph your results, using the weight of the shoe as the independent variable (x-axis), and force of friction as the dependent variable (y-axis). Using Graphical Analysis plot the Friction vs. Normal Force (weight) and determine the relationship.( i.e: determine the slope of the line) for both Static and Kinetic friction. Graph both static values and kinetic values on the same graph. What can you conclude from your results concerning the relationship of weight and friction? Shoe #1 on Surface #1 Part 1 Does wt. Affect Friction? Shoe Shoe+ 100g Shoe +200g Shoe+300g Shoe+400g Shoe +500g Shoe +600g Shoe +700g Shoe + 800g Shoe + 900g Shoe + 1kg Koenig Physics 2014-15 Weight (N) Static friction (N) Sliding friction (N) Shoe #1 Surface #2 Part 1 Does wt. Affect Friction? Weight (N) Static friction (N) Sliding friction (N) Shoe Shoe+ 100g Shoe +200g Shoe+300g Shoe+400g Shoe +500g Shoe +600g Shoe +700g Shoe + 800g Shoe + 900g Shoe + 1kg The friction equation states Ff = FN where Ff is the force of friction, and FN is the normal force. This is the equation of a straight line with the slope equal to the coefficient of friction . (y=mx+b) Thus, a graph of friction as a function of weight should produce a straight line with a slope equal to the coefficient of friction. 1) Does a graph of your data produce a straight line? 2) Determine the coefficient of friction by measuring the slope. 3) Inspect your results in the table and describe the relationship between weight and static friction, and between weight and kinetic (sliding) friction 4) Will the soles of your shoes wear out faster when hiking or back- packing with a pack on your back? Explain. 5) Do you think the coefficient of friction is different for each surface the shoe is in contact with? Give reasons for your answer. 6) Do you think the surface area of contact affects friction? Explain. Answer all questions to this lab. 1 lab for each person(no more than 4 persons per group) All answers to questions to be typed. Graph should show all calculations (if printing is unavailable graph paper will be used) Attach the data table to your graph. Be sure to include names of all lab partners on the report. Koenig Physics 2014-15 Koenig Physics 2014-15