Lab 3. Static and Kinetic Friction. Whenever two surfaces that are in contact with each other try to move pass one another there is a force that resists the motion. In some case you could push on an object trying to move it and the object doesn't move. The force of static friction fo balances your force. This is because in order to move an object you need to apply a force larger or equal to the maximum possible static friction, famas. Once moving the object still offers some resistance and if you stop pushing the object will immediately start to slow down to a stop, the force responsible for this behavior is the force of kinetic friction, f- On the other side if you push with a force equal to the kinetic friction the object will move with constant velocity. In this experiment, you will use a simulator to study static friction and kinetic friction. The static friction force represents the peak of the graph F vs t and the kinetic friction force will be the mean value of the second part of the graph when the force is contact and lower than the peak. Here is the link for the simulator, https://www.thephysicsaviary.com/Physics/Programs/Labs/ForceFriction/index.html Purpose of the lab: To find the graphical and mathematical relationship between the forces of maximum static and kinetic frictions and the normal force on the objects, to determine the coefficients of static and kinetic frictions for the surface being studied. Mass Tray . Pull This is the diagram of the experiment, the simulator controlling the acting force through the force sensor connecting to the interface and will give us the graph F vs time. To understand the theory study the section 6.1, 6.2 from the book. The static friction force is F.=:FN (1), F: is the static friction force, us is the coefficient of static friction and Fy is the normal force. The kinetic friction force is Fx=AFN (2), Fr is the kinetic friction force, Ak is the coefficient of kinetic friction and FN is the normal force. The normal force in a horizontal surface when the pulling force is acting in horizontal direction will be equal to the weight ,so FN= mg The simulator will give you a graph like: HFA the peak is the static friction Mean value is the kinetic friction. t Steps to practice with the simulator. 1. Open the simulator and select begin. 2. In the left part you see with blue letters different types of interacting surfaces such as: Aluminum on steel, Glass on glass, graphite on graphite, wood on the table rubber on concrete and rubber on ice 3. You have the option to select different masses, using the arrow you can increase or decrease the mass of the experiment. 4. Once you select the surface and the mass you can click on start and using the graph F vs t to determine the static friction and kinetic friction force. Procedure. Part 1 Rubber on Concrete . In this section, you will measure the peak static friction force and the kinetic friction force as a function of the normal force on the block. In each run, you will pull the block as before, but by changing the masses on the block, you will vary the normal force on the block. 1. Select the surface rubber on concrete. 2. Select mass of smallest value. 3. Click start and determine what is the value of static friction, fill out the value in data table 1A and kinetic friction in data table 1B. 4. Change the mass to next five values and fill out the corresponding values of static and kinetic friction. 5. Calculate the EN in all cases and fill out the data table 1 and 2. Repeat steps 1 -5 with another surface "aluminum on steel "and complete the corresponding data tables 2A and 2B.Rubber on Concrete Data Table 1A Data Table 1B Maximum Static Kinetic Friction. Friction Peak Normal Normal mass Static mass Peak Static force force (m) Kg Friction [m) Kg Friction [N) (N) (N) IN} Part 2. In this part we will repeat the steps 1 to 3 using the surface aluminum on steel. In this case your will complete the data table 2A and 2B. Aluminum on steel. Data Table 2A Data Table 2B Maximum Static Kinetic Friction. Friction. Normal Peak Normal mass mass force Static Peak Static force [m) Kg Friction Friction [N) (N) (m) Kg (N) [N} Analysis for part 1. 1. The coefficient of friction is a constant that relates the normal force between two objects (blocks and table) and the force of friction. Based on your observation, would you expect the coefficient of static friction to be greater than, less than, or the same as the coefficient of kinetic friction? Explain.2. Use excel, logger pro or other graphing method with the data table 1A graph the maximum static friction force (vertical axis) vs. the normal force (horizontal axis). Comment on the relationship and write the corresponding equation. Explain the meaning of the slope. 3. Graph the relationship between the force of kinetic friction and normal force for data table 1B. Comment on the relationship and write the corresponding equation. Explain the meaning of the slope. 4. Do the slope from Graph 1A and 1B are different? Explain. 5. Find in internet the coefficient of static friction of rubber in concrete and compare with the experimental value obtained from the graph in point 2. Determine the percent error. 6. Find in internet the coefficient of kinetic friction of rubber in concrete and compare with the experimental value obtained from the graph in point 3. Determine the percent error. Analysis for part 2. Repeat all points 1 to 6 from analysis part 1 using the data table 2A and 2B. Procedure part 3. We will calculate the coefficient of friction using the formula (1) and (2) for other surfaces. 1. Set up the surface rubber on ice and pick up any mass. 2. Click on start and determine the static friction force and complete the row on data table 3A and the value of kinetic friction force in data table 3B. 3. Calculate and fill out the normal force for the selected mass in both data table 3A and 3B. 4. Run the simulator with the rest of surfaces and selected mass and complete the date table 3A and 3B. Maximum Static Friction. Data Table 3A Normal Peak Static % surface mass [kg] force Friction [N) (N) experimental value of error ustatic rubber on ice glass on glass graphite on graphite wood on the table 4Kinetic Friction. Data Table 3B Normal mass [Kg] force Kinetic surface (N) Friction [N)| experimental value of error ukinetic rubber on ice glass on glass graphite on graphite wood on the table Analysis. Part 3. 1. Calculate the coefficient of static friction using the formula (1) and fill out in data table 3A. 2. Calculate the coefficient of kinetic friction using the formula (2) and fill out in data table 3B. 3. Find in internet the actual value for the corresponding value of the coefficient of static friction and calculate the % error for all rows in data table 3A 4. Repeat the same for data table 3B for coefficient of kinetic friction. 5. Find in internet the actual value for the corresponding value of the coefficient of static friction and calculate the % error for all rows in data table 34 6. Does the force of kinetic friction depend on the weight of the block? Explain. 7. Does the coefficient of kinetic friction depend on the weight of the block? Show all formulas and calculations when needed. Write the conclusion for the lab