# Friction

## Overview

Friction is a fundamental concept in the world of Physics that plays a crucial role in everyday phenomena. It can be classified into two main types: static friction and dynamic friction. Static friction occurs when two surfaces are at rest relative to each other, resisting the initiation of motion. On the other hand, dynamic friction comes into play when two surfaces are in motion relative to each other. Understanding the differences between these types of friction is essential in various mechanical systems and applications.

One key parameter in the study of friction is the coefficient of limiting friction, which quantifies the maximum frictional force that can be exerted between two surfaces before motion occurs. Determining this coefficient involves experimental methods and careful analysis to ensure accurate results. The coefficient of limiting friction is a critical value used in designing structures, machines, and systems to prevent unnecessary slippage or damage due to excessive friction.

Friction, while necessary in many scenarios, also comes with its advantages and disadvantages. On the positive side, friction provides stability, enabling us to walk, drive vehicles, and grip objects. However, excessive friction can lead to energy loss, wear and tear on surfaces, and inefficiencies in mechanical systems. Understanding these pros and cons helps engineers and designers optimize frictional effects for optimal performance.

To address the challenges posed by friction, there are various methods to reduce friction in systems and applications. Strategies such as lubrication, polishing surfaces, and using low-friction materials can help minimize frictional forces and improve efficiency. By exploring ways to mitigate friction, industries can enhance the lifespan and performance of their products while reducing energy consumption.

In the realm of fluid dynamics, viscosity and terminal velocity play significant roles in understanding the behavior of fluids. Viscosity refers to a fluid's resistance to flow, influenced by factors such as temperature and molecular interactions. The concept of terminal velocity relates to the maximum speed reached by an object falling through a fluid when the gravitational force equals the drag force. These phenomena are crucial in various fields, including aerodynamics and fluid mechanics.

Stoke's Law, a principle named after the renowned scientist George Stokes, provides a mathematical expression for the viscous drag force experienced by spherical objects moving through a fluid at low Reynolds numbers. By applying Stoke's Law, scientists and engineers can analyze the behavior of particles in viscous fluids and understand the dynamics of systems where fluid resistance is a significant factor.

## Objectives

2. Suggest Ways by Which Friction Can Be Reduced
3. Analyse Factors that Affect Viscosity and Terminal Velocity
4. Determine the Coefficient of Limiting Friction
5. Differentiate Between Static and Dynamic Friction
6. Apply Stoke’s Law

## Lesson Note

Friction is a force that opposes the motion of objects sliding or rolling over each other. It is an essential force in our daily lives and plays a crucial role in various physical phenomena.

## Lesson Evaluation

Congratulations on completing the lesson on Friction. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

1. What is the difference between static and dynamic friction? A. Static friction occurs when an object is moving, while dynamic friction occurs when an object is at rest. B. Static friction is a contact force, while dynamic friction is a non-contact force. C. Static friction opposes the initial motion of an object, while dynamic friction opposes the object's motion. D. Static friction is greater than dynamic friction. Answer: Static friction opposes the initial motion of an object, while dynamic friction opposes the object's motion.
2. How is the coefficient of limiting friction determined? A. By dividing the static friction by the normal force acting on the object. B. By dividing the kinetic friction by the normal force acting on the object. C. By dividing the normal force by the applied force. D. By dividing the applied force by the static friction. Answer: By dividing the static friction by the normal force acting on the object.
3. What are the advantages of friction? A. Friction reduces wear and tear on surfaces. B. Friction helps in walking on the ground. C. Friction enables the gripping of objects. D. Friction increases energy efficiency. Answer: Friction enables the gripping of objects.
4. How can friction be reduced? A. By increasing the roughness of the surfaces in contact. B. By applying oil or lubricants to surfaces. C. By increasing the mass of the objects. D. By increasing the force of interaction between the surfaces. Answer: By applying oil or lubricants to surfaces.
5. What factors affect viscosity and terminal velocity? A. Temperature and pressure. B. Surface area and volume. C. Mass and weight. D. Speed and acceleration. Answer: Temperature and pressure.
6. How is Stoke's law applied? A. It describes the motion of objects in circular paths. B. It predicts the terminal velocity of an object falling in a fluid. C. It determines the coefficient of limiting friction. D. It calculates the work done by a force. Answer: It predicts the terminal velocity of an object falling in a fluid.

## Past Questions

Wondering what past questions for this topic looks like? Here are a number of questions about Friction from previous years

Question 1

You are provided with a battery of e.m.f, Estandard resistor, R, of resistance 2 ? $\mathrm{?}$, a key, K, an ammeter, A, a jockey, J, a potentiometer, UV, and some connecting wires.

(i) Measure and record the emfE, of the battery.

(ii) Set up the circuit as shown in the diagram above with the key open.

(iii) Place the jockey at the point, U, of the potentiometer wire. Close the key and record the reading, i, of the ammeter.

(iv) Place the jockey at a point on the potentiometer wire UV such that d = UT = 30.0 cm.

(v) Close the circuit, read and record the current, I, on the ammeter,

(vi) Evaluate I1 ${}^{1}$.

(vi) Repeat the experiment for four other values of d = 40.0 cm, 50.0 cm, 60.0 cm and 70.0 cm. In each case, record I and evaluate I1 ${}^{1}$.

(vii) Tabulate the results

(ix) Plot a graph with d on the vertical axis and I on the horizontal axis stalling both axes from the origin (0,0).

(x) Determine the slope, s, of the graph.

(xi) From the graph determine the value I1 ${}_{1}$, of when = 0. (ci) Given that=s, calculate 8.

(xii) State two precautions taken to ensure accurate results.

(xii) Given that E?  = s, calculate ??
.

(b)(i) Write down the equation that connects the resistance, R, of a wire and the factors on which it depends. State the meaning of each of the symbols.

(ii) An electric fan draws a current of0.75 A in a 240 V circuit. Calculate the cost of using, the fan for 10 hours if the utility rate is \$ 0.50 per kWh.

Question 1

If an object just begins to slide on a surface inclined at 30º to the horizontal,the coefficient of friction is?

Question 1

In which of the following is the expansion of solids a disadvantage?

Practice a number of Friction past questions