3.04 Friction Coefficient Lab Handout-2

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San Jose State University *

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Mechanical Engineering

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Apr 3, 2024

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Name of Student: Name of Teacher: Coefficient of Friction Virtual Lab Introduction: This 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. The Friction Coefficient simulation : http://thephysicsaviary.com/Physics/Programs/Labs/ForceFriction/index.html Procedure 1. When you are ready to start the experiment, click on the Begin button. 2. Choose a mass of 221g (or any mass in the 200’s) by clicking on the arrows found in the center of the simulation. Be sure to record this value in the data table. Make sure to convert it into kilograms. 3. Choose the type of surface by clicking on the names of the type of surfaces listed. 4. Click the Start button. 5. Take a screenshot of the first graph that you produce. You may have to scroll down on the Web page to see the graph. 6. The first section of the graph represents static friction. Notice that the static friction value increased until it reached a maximum value. Record that maximum value in your data table. 7. The second relatively horizontal portion of the graph represents the kinetic force of friction. Record a force that is vertically in the middle of the series of points. 8. Repeat the steps choosing two other values of masses around 425 g and 725 g. You will have to press the Reset button after every trial. 9. Choose two other types of surfaces and complete three trials using the same masses as you did with Rubber on Ice. 10. On completing the data, do the calculations. Determine the normal force. (You might need to draw the FBD to see what the equation is in the y- axis) Calculate the coefficient of friction using the equation. Data
Name of Student: Name of Teacher: Table I: Surface - Rubber and Ice Mass (kg) Normal (N) Maximum Static Friction (N) Coefficient of Static Friction Kinetic Friction (N) Coefficient of Kinetic Friction 0.215 2.11 0.25 0.118 0.15 0.071 0.425 4.17 0.50 0.119 0.30 0.072 0.725 7.11 0.80 0.113 0.50 0.070 Table 1 FBD and Calculations:
Name of Student: Name of Teacher: Table 2: Surface – Aluminum on Steel Mass (kg) Normal (N) Maximum Static Friction (N) Coefficient of Static Friction Kinetic Friction (N) Coefficient of Kinetic Friction 0.215 2.11 1.3 0.616 1.0 0.474 0.425 4.17 2.5 0.599 2.0 0.480 0.725 7.11 4.5 0.633 3.3 0.464 Table 2 Calculations:
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Name of Student: Name of Teacher: Table 3: Surface – Glass on Glass Mass (kg) Normal (N) Maximum Static Friction (N) Coefficient of Static Friction Kinetic Friction (N) Coefficient of Kinetic Friction 0.215 2.11 1.9 0.900 0.8 0.379 0.425 4.17 3.5 0.839 1.6 0.384 0.725 7.11 6.0 0.844 2.9 0.408 Table 3 Calculations: Questions 1. From the graph you saved, explain why objects seem to suddenly jerk forward when you push or pull on them. When you push or pull an object and it suddenly jerks forward, it is due to a shift from static friction to kinetic friction. Static friction prevents the object from moving when at rest, while kinetic friction opposes motion once the object starts moving. The abrupt motion occurs when the force applied overcomes the static friction, causing the object to transition to kinetic friction, resulting in a sudden acceleration or jerk. This transition is more noticeable when there is a significant difference between the coefficients of static and kinetic friction between the surfaces in contact . 2. What effect did the mass of the object have on the coefficient of friction? The mass of the objects did not directly affect the coefficient of friction between the objects and their surfaces. The combination of mass and the gravitational acceleration contribute to the normal force, which then affects the coefficient of friction. 3. What effect did the mass have on the force of friction? The mass of an object directly affected the force of friction by influencing the normal force. As the mass of an object increased, the normal force exerted on the surface also increased. This, in turn, led to a higher frictional force due to the direct proportionality between the normal force and the force of friction. 4. What effect did different surfaces have on the coefficient of friction?
Name of Student: Name of Teacher: Rougher surfaces exhibited higher coefficients of friction, providing greater resistance, while the smoother surfaces tended to have lower coefficients, allowing for easier movement. The choice of materials of surfaces and their textures significantly influences the coefficient of friction and can impact how objects interact with surfaces. 5. What effect did different surfaces have on the force of friction? The rougher surfaces had high friction coefficients which significantly impacted the force of friction between the objects and the surfaces. The surfaces with higher coefficients of friction resulted in stronger frictional forces, making it more challenging to move objects across them. Conversely, surfaces with lower coefficients of friction generated lower frictional forces, making it easier to slide objects.