/ 50 Lab Cube Names of Team Purpose Students will explore static and kinetic frictional forces by studying different types of surfaces and how they perform under constant force. Students will also learn how to calculate the coefficient of friction forces. Objectives: A) Define & Explain two types of friction and how they are measured B) How to calculate the coefficient of friction C) How to read and use a spring scale Materials cube with four surfaces Sandpaper, vinyl, paper, & wood Spring Scale, Plank of wood Symbol and their meanings F p = Pulling F w = Weight F n = Normal f s = f k = = = Definitions: F W = -mass x acceleration due to gravity [F=-mg] F n = mass x acceleration due to gravity [F=mg] f s = The amount of force needed to start an object in motion f k = The amount of force needed to maintain the motion an object. Free Body Diagram Directions and placement of forces F n = Reaction to surface, points up This lab replaces a class lecture on friction. You are requested to record key learnings from this lab into your notebook and update your table of content. f s / f k = al forces, opposite of motion F p = Pulling/Pushing F w = Weight (down) 1 P age
Lab Cube Information about - the resistance force occurring when one surface encounters another surface in motion is a force and it affects motion by slowing objects down & heats them up. acts in a direction that is opposed (opposite) to the motion. The strength of the frictions forces depends on the roughness of the surfaces and is measure by the coefficient of friction. Procedures Part I How to read the spring scale 1) Examine the spring scale and determine how to read the scale values. Place a number next to each line indicating its value in Newton s or grams. Seek your teacher approval before moving on. Newton s (N) Grams (g) 0 0 Teacher Approval 0.25 25 Part II Weight of Cube 2) Hold the spring scale vertical with the hook on the bottom 3) Make sure the spring scale is zeroed 4) Hang the cube from the bottom of the scale & record the readings Cube Mass in grams = Weight in Newton s = F W = F N = 5) Show how the spring scale converts from grams to Newton s. Use 10 m/s 2 2 P age
Lab Cube Part III Determining force of friction 6) Position the wooden plank so the word cube is facing up (visible) 7) Examine the cube surfaces and identify each surface: vinyl, sandpaper, paper and wood. 8) Position the cube at one end of the plank with the vinyl side down (touching the plank) 9) Attach the spring scale to the cube. Make sure the scale is level. 10) Make sure the spring scale reads zero just before pulling. 11) Pull on the spring scale with a steady force and maintain the same force throughout the pull. You may want to practice several times before recording your results. The more practice, the better the results. 12) Make observations Record the value of static friction by noticing the amount of force needed to start the cube in motion. Record the value of kinetic friction by noticing the amount of force needed to keep the cube in motion. and kinetic values should never be the same. Repeat two more times and average the results. Vinyl al al 13) Calculate the coefficient of friction for both static and kinetic by using the following equations (use average forces): Show your work. = f s / F n = = f k / F n = 3 P age
14) Repeat for Sandpaper, paper & wood Lab Cube Paper al al Wood al al Sandpaper al al 15) Carefully put all of your equipment away. Make sure the springs scales are in their boxes and the cubes are in the plastics bags 4 P age
Lab Cube Questions: More details leads to more points (use complete sentences) 1) Describe in detail your results between static and kinetic friction. 2) Describe in detail your results between the four different types of surfaces. 3) Using inertia, describe why static and kinetic frictions were different. 4) Identify four points of error in the lab and identify as human, systemic and random. 5) Describe how you could calculate the speed of the cube when kinetic friction was in force. 5 P age