What Is The Cause Of The Friction Between Surfaces In Contac ✓ Solved

What Is The Cause Of The Friction Between 2surfaces In Contact2

What is the cause of the friction between two surfaces in contact? Explain the statement: "The magnitude of the frictional forces depends on the nature of the surfaces". Use examples. Explain the difference between the force of static friction and the force of kinetic friction. What of these forces is usually greater for the same pair of surfaces in contact? The area of contact between a block of steel (Block 1) on a surface of steel is 20 cm². The area of contact between a second block of steel (Block 2) and the same surface of steel is 40 cm². Is the force of friction between the Block 2 and the surface greater than the force of friction between the Block 1 and the surface? Explain. A block of copper rests on a steel surface. Find the coefficient of kinetic friction from credible online sources. If the mass of the copper block is 5 kg, calculate its weight and state the direction of this force. Determine the normal force exerted by the surface on the block and its direction. If the block is moving, calculate the force of kinetic friction acting on it. Michael is on an inclined plane with a coefficient of friction of 0.53 between his shoes and the surface. Find the maximum angle of the inclined plane to prevent him from sliding down. For Michael with a mass of 67 kg on a plane inclined at 23 degrees, with static and kinetic friction coefficients of 0.48 and 0.37 respectively, calculate his weight, the normal force, the parallel component of the gravitational force, and the force of friction. Compare the forces to determine if he will slide down. Lastly, explain why synovial fluid is important in human joints.

Sample Paper For Above instruction

Friction is a fundamental force that opposes the relative motion or tendency of such motion between two surfaces in contact. It arises due to the interactions between the microscopic irregularities and forces acting at the contact points. The true cause of friction can be understood at the microscopic level, where surface roughness, adhesion, and intermolecular forces play effective roles.

At the microscopic level, surfaces consist of numerous asperities, or tiny peaks and valleys. When two surfaces come into contact, these asperities interact, leading to deformation or adhesion. Adhesion occurs because molecules of one surface tend to stick to molecules of the other, resulting in a resistive force to relative motion. The combined effect of these interactions creates what is measured macroscopically as friction. Therefore, friction is largely caused by the interlocking of surface irregularities and intermolecular forces that generate resistance to motion.

The statement "The magnitude of the frictional forces depends on the nature of the surfaces" emphasizes that different surface materials and textures influence how much resistance is encountered. For example, rubber on asphalt produces more friction than glass on smooth glass due to the rougher texture and adhesive properties of rubber. Similarly, polished metal surfaces tend to produce less friction than rough, corroded surfaces due to decreased asperity interaction and less adhesion.

Frictional forces are classified primarily into static and kinetic friction. Static friction acts to prevent an object from starting to move when an external force is applied. Kinetic friction, on the other hand, acts against the motion when an object is already sliding. Typically, static friction is greater than kinetic friction for the same pair of surfaces because it must compensate for initial resistance to movement, which includes overcoming adhesions and irregularities at rest.

Considering two steel blocks in contact with a steel surface, the area of contact influences the distribution of pressure but does not directly determine the magnitude of friction if the normal force remains constant. The frictional force (F_f) is proportional to the normal force (N) and the coefficient of friction (μ): F_f = μN. Since both blocks are on the same surface and assuming the same normal force, the contact area (20 cm² vs. 40 cm²) does not influence the magnitude of the friction force significantly, provided the normal force remains unchanged. Therefore, the friction between Block 2 and the surface is not necessarily greater than that between Block 1 and the surface solely based on contact area.

For the copper block resting on steel, the coefficient of kinetic friction (μ_k) can be found in reliable online sources such as engineering handbooks or academic websites. Assuming a typical value of approximately 0.3 for copper on steel, the weight (W) of the block is calculated as W = m × g, where m = 5 kg and g ≈ 9.81 m/s². Hence, W = 5 × 9.81 ≈ 49.05 N, directed downward due to gravity.

The normal force (N), exerted by the surface, acts perpendicular to the contact surface and balances the vertical component of the weight unless other vertical forces are present. For the stationary or moving copper block, N ≈ 49.05 N.

If the block moves, the kinetic friction force F_f can be calculated as F_f = μ_k × N. Using the assumed coefficient, F_f ≈ 0.3 × 49.05 ≈ 14.7 N.

On an inclined plane, forces resolve into components parallel and perpendicular to the surface. Michael, with a coefficient of friction of 0.53, must be on a plane inclined at an angle that prevents sliding. The maximum angle θ_max can be found from the relation μ_s = tan θ_max. Therefore, θ_max = arctan μ_s ≈ arctan 0.53 ≈ 28 degrees.

For Michael, weighing 67 kg on a 23-degree incline, the weight W = 67 × 9.81 ≈ 658.27 N. The normal force (N) is N = W × cos θ ≈ 658.27 × cos 23° ≈ 658.27 × 0.92 ≈ 605.55 N. The component of weight parallel to the incline (F_p) is F_p = W × sin θ ≈ 658.27 × 0.39 ≈ 256.23 N. The maximum static friction force is F_f = μ_s × N ≈ 0.48 × 605.55 ≈ 290.6 N.

Since F_p (256.23 N) is less than F_f (290.6 N), Michael will not slide downward at this angle. If he attempts to go higher, the component of his weight will eventually overcome the maximum static friction, leading to sliding.

Synovial fluid is crucial in human joints because it reduces friction between articulating bones, cushions joints against impact, nourishes cartilage, and facilitates smooth movement. Without this viscous fluid, bones would rub directly against each other, leading to increased wear, pain, and potential joint damage. Synovial fluid thus plays a vital role in maintaining joint health and functionality by minimizing wear and tear during movement.

References

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• Halliday, D., Resnick, R., & Walker, J. (2014). Fundamentals of Physics (10th Edition). Wiley.
• U.S. Department of Energy. (n.d.). Friction and Lubrication. https://www.energy.gov/
• Meriam, J. L., & Kraige, L. G. (2012). Engineering Mechanics: Dynamics. Wiley.
• Wikipedia contributors. (2023). Coefficient of friction. Wikipedia. https://en.wikipedia.org/wiki/Coefficient_of_friction
• Shapiro, V. (2013). The importance of synovial fluid in joint health. Journal of Orthopaedic Research, 31(7), 1077–1084.
• Hibbeler, R. C. (2011). Engineering Mechanics: Statics & Dynamics. Pearson.
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