AP Physics 1 Virtual Lab - Friction

Lab: FrictionObjective: Students will determine the effect surface contact area has on friction.Students will develop an equation relating the frictional force and the normal force exerted on an object.Pre LabDraw all of the forces that are acting on a wooden crate when a student pushes the crate so that it is just about to start moving--but still at rest--on a rough surface.Remember that the size of your vectors indicates the magnitude of the forces.Double click on the picture to edit.F of personF of frictionF of gravityF of normalWhat claim can you make about the student’s pushing force and the force of static friction in question 1?Explain your reasoning.The students pushing force is equal in magnitude to the force of static friction. The force is not yet great enough to move the object.Draw all of the forces that are acting on the crate when a student pushes the wooden crate at a constant velocity across a rough surface.Remember that the size of your vectors indicates the magnitude of the forces.F of personF of frictionF of gravityF of normalWhat claim can you make about the student’s pushing force and the force of kinetic friction in question 3?Explain your reasoning.The student’s pushing force is equal in magnitude to the force of kinetic friction because the block is moving at a constatn velocity and has an acceleration of 0.Using the SimulationOpen up this Virtual Lab on the Force of FrictionThis lab will let you determine the coefficients of static friction and kinetic friction between different surfaces. You will be pulling with increasing tension until the object begins to slide and then you will keep the object moving at a slow steady speed. The graph below the action is a graph of the tension in the string.Change the mass of the block by clicking on the arrows beneath the words ‘Object Mass’Change the two surfaces by clicking on the words ‘Type of Surfaces’Change the surface area of the block by clicking on the blockPart 1: Does the Surface Area in Contact with a Surface affect the Force of Friction?Conduct an experiment to see how the surface area of the block that is in contact with the surface affects the force of friction.What will be kept constant in your experiment?Mass of the block, type of surface, and the blockMaximum Force of Static FrictionFF S Max (N)Force of Kinetic FrictionFF K(N)Surface Area 10.110.075Surface Area 20.110.075Surface Area 30.110.075Surface Area 40.110.075Surface Area 50.110.075What is the relationship between the surface area in contact with the surface and the force of friction?There is no relationship between the surface area and the force of friction.Part 2: The Coefficient of Static FrictionConduct an experiment to determine the coefficient of static friction between two materials.Which two materials are you examining?Rubber and IceMass of Blockm(kg)Maximum Force of Static FrictionFF S Max (N)Normal ForceFN (N)Mass 1.1000.110.998Mass 2.2790.312.78Mass 3.3430.383.43Mass 4.5370.615.36Mass 5.7180.817.17GraphCreate a graph using Google Spreadsheet that will allow you to develop an equation relating the force of static friction on your block and the normal force exerted on your block.Put force of friction on the vertical axis and normal force on the horizontal axis. Copy and paste the graph in the space below.Analysis and ConclusionIn the space below, record your equation relating force of friction and the normal force.FFK = 0.114(FN) - 5.97E-03Part 3: Kinetic FrictionConduct an experiment to determine the coefficient of kinetic friction between two materials.Use the same materials as in the previous partMass of Blockm(kg)Force of Kinetic FrictionFF K (N)Normal ForceFN (N)Mass 1.1000.0750.998Mass 2.2790.202.78Mass 3.3430.263.43Mass 4.5370.405.36Mass 5.7180.557.17GraphCreate a graph using Google Spreadsheet that will allow you to develop an equation relating the force of kinetic friction on your block and the normal force exerted on your block. Put force of friction on the vertical axis and normal force on the horizontal axis. Copy and paste the graph in the space below.Analysis and ConclusionIn the space below, record your equation relating force of friction and the normal force.FFK = 0.0835(FN) + 0.0902Post LabThe slope of your graph should have been different for the two previous graphs. In everyday terms, what does it mean that the slope of one graph was higher than the other?It means that the higher slope graph increases at a higher rate than the graph of the smaller slope. So in this case, As Normal Force increases, Static energy increases at a higher rate because it’s graph has a greater slopeLook up the term Coefficient of Friction. Explain the significance of the different slopes using the coefficient of friction.The slope of the graphs represent the relationship between the Normal force and the force of friction because it is a linear relationship. The Coefficient of Friction is equal to the value of the slope of the graphs, because the graphs have the normal force as the independent variable and the force of friction as dependent. There is a Coefficient of Friction for both Static, and Kinetic friction, and µK<= µS because the slope of the static friction graph is greater.Fill in the blanks to complete the paragraph below.It makes sense that the floor pushing harder on the wooden crate would cause more friction between the floor and the wooden crate. Therefore, the force of friction would increase whenNormal force is increased. If the floor were made from a rougher surface, it would make sense that there would be more friction between the floor and the wooden crate. Therefore it makes sense that the force of friction would increase whenNormal force is increased. Taking both these factors into account, I believe the equation for the force of friction should be F = µN .Support your answer to the previous question using evidence from your graphs.Normal force is the force exerted by the floor onto the object, so if the floor pushed harder against the object, then the normal force would be greater. The first graph shows that when normal force is increased, the static friction force increases. The last second graph also shows that when normal force is increased, the force of kinetic friction is increased.Looking at the graphs, we can see that normal force and the force of friction have a linear relationship. This means that there must also be a constant in the equation. The coefficient of friction is equal to the two slopes of the graphs. Using the two graphs, we can conclude that the relationship between the normal force and friction force is F=µN where F = force of friction, µ = coefficient of friction, and N = normal force.