Answer Happy

Part One: Coefficients of Friction 1. From the library of activities available for this class on Pivot Interactives, open the one titled Friction on an Inclined Plane. Play the video within this activity and watch what happens. 2. Click on the Tools Icon ( ) to see the choices of measuring instruments you have. Remember that you open each tool by clicking on its icon, and that you can move the tools around on the screen as needed. The ruler tool can also be rotated; it doesn't have to remain horizontal. 3.(a) Reset the video to the start, then advance it where the Einstein figure just starts to move down the incline. Recall that you can use either the slider bar or the forward and back buttons to move the video to whichever frame you wish. Click on the Angle tool icon, and then move the protractor so you can measure the angle of incline that made the Einstein figure just start into motion. Measure this angle to the nearest 0.5 degree (b) Close the Angle tool, and open the Ruler and Stopwatch/Timer tools. Use these to measure both how far down the incline Einstein slides (to the nearest 0.001 meter, and the time this takes. Make these measurements for the longest distance and time possible, but before the feet of the Einstein figure touch the surface of the table. Part Two: Drag on Falling Coffee Filters 1. From the library of activities available for this class on Pivot Interactives, open the one titled Falling Coffee Filters. Record the mass of each of the six stacks of coffee filters shown in the video within the activity. Convert the grams to kilograms, and don't drop any digits 2. Click on the Tools Icon (). Then open the Stopwatch tool and the Vertical Ruler tool (Use the 2 from the right of the two vertical rulers available) Play the video and measure the elapsed time it takes each stack to move from a position of 100.0 cm to 140.0 cm. (Move the vertical ruler so that the zero mark is at the bottom part of each stack before you watch that stack fall). 3. Remove the vertical ruler tool, and then open the other one (which is the tool icon furthest to the left). Click on the ruler; this will bring up a frame around the ruler that will allow you to rotate the ruler

Rotate the ruler so that you can now use it to measure the diameter of a coffee filter at its widest point, to the nearest 0.001 meter. Analysis & Calculations Be sure to apply the "rounding rules" (as introduced in our Chapter 1 discussions) to any numerical calculations. Part One 1. (a) When the angle of incline of the ramp is such that the Einstein figure is on the verge of moving down the ramp, the coefficient of static friction can be shown to be equal to ustane, where is the angle of inclination (1) Use equation (1) to find the value of the coefficient of static friction (b) Calculate the acceleration of Einstein down the ramp, which is equal to (twice the distance moved down ramp) divided by (time to move squared). Call this acceleration ax The coefficient of kinetic friction for the situation used in the experiment is the = tane - My e cose (2) Use equation (2) to find the value of the coefficient of kinetic friction Part Two 1. (a) Calculate the weight of each of each stack by multiplying the mass by the acceleration due to gravity (b) Calculate the terminal speed of each of the six stacks by dividing the distance each travelled (0.400 meters) by the elapsed time. 2. (a) Calculate the cross-sectional area of the coffee filters at their widest point. (b) When terminal speed has been reached the size of the weight of each coffee filter stack

Use equation (1) to find the value of the coefficient of static friction (b) Calculate the acceleration of Einstein down the ramp, which is equal to (twice the distance moved down ramp) divided by (time to move squared). Call this acceleration ax. The coefficient of kinetic friction for the situation used in the experiment is Mx = tan - ax g cose (2) Use equation (2) to find the value of the coefficient of kinetic friction Part Two 1. (a) Calculate the weight of each of each stack by multiplying the mass by the acceleration due to gravity (b) Calculate the terminal speed of each of the six stacks by dividing the distance each travelled (0.400 meters) by the elapsed time. 2. (a) Calculate the cross-sectional area of the coffee filters at their widest point. (b) When terminal speed has been reached, the size of the weight of each coffee filter stack equals the size of the drag force it experiences. Determine the drag coefficient for each filter stack. (Hint: Review Equation 5.12, and also Table 5.3, from the course textbook).

Part One: Coefficients of Friction Distance Time Angle of Inclination 45 20 0.4 Part Two: Drag on Falling Coffee Filters Number of Filters 1 2 3 4 5 6 Mass 0.002067 0.003113 0.004124 0.005190 0.006211 0.001035kg 1.770833sec Time 1.233333 1.054167 0.941667 0.837500 0.812500 Diameter of coffee filter at widest point: 130cm Results Part One Coefficient of Static Friction Acceleration Coefficient of Static Friction Part Two Cross-sectional area of coffee filter: Click here to enter text. Number of Filters 1 2 3 5 6 Weight Terminal Speed Drag Coefficient

Questions for Experiment #3: "Friction and Air Resistance" 1. (a) Draw and label a free-body diagram for the Einstein figure in Part One, when it was on the verge of riotion (b) Now, apply Newton's 2nd law to the Einstein figure and derive Equation (1). Be sure to clearly show all of the steps in your derivation. 2. (a) Draw and label a free-body diagram for the Einstein figure in Part One, when it was in motion down the incline. (b) Now, apply Newton's 2nd law to the Einstein figure and derive Equation (2). Be sure to clearly show all of the steps in your derivation 3. (a) Explain why you would expect the drag coefficients from Part Two to all have the same value. (b) Suppose you turned the coffee filters upside down (so that their widest parts were first to go through the air as they fell) and then repeated the 2nd part of the experiment. What effect would this have on the sizes of the terminal velocities, and on the sizes of the drag coefficients? Provide the physics-based reasoning behind your answer.