Lesson Notes By Weeks and Term - Senior Secondary 1

Friction

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Term: 1st Term

Week: 5

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:       

Subject:      Physics

Topic:-       Friction

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Define Friction
  2. State the laws Governing Solid Friction
  3. Outline the advantages & Disadvantages of Friction
  4. Discuss ways of reducing Friction

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S ACTIVITY

STEP 1

INTRODUCTION

The teacher reviews the previous lesson on motion

Students pay attention

STEP 2

EXPLANATION

He defines friction. He states the laws governing solid friction

 

Students pay attention and participates

STEP 3

DEMONSTRATION

He outlines the advantages and disadvantages of friction and discusses ways of reducing friction

Students pay attention and participate

STEP 4

NOTE TAKING

The teacher writes a summarized note on the board

The students copy the note in their books

 

NOTE

FRICTION

Friction (Fr) is defined as an opposing force which acts at the surface of two objects or bodies in contact. It is simply force of opposition. We have two types of friction:

  1. Static friction, Fs
  2. Dynamic friction, Fd.

 

NOTE: Fs is greater than Fd for object at rest while Fd is greater than Fs for object in motion.

 

LAWS GOVERNING SOLID FRICTION

  1. Friction opposes the relative motion of two surfaces in contact
  2. It is independent of the area of the surface of contact
  3. It depends on the nature of the surface
  4. It is proportional to normal reaction (R)
  5. It is independent of relative velocity between the surfaces

          Fr α R

          Fr = μR                1

Where: Fr=frictional force: μ=coefficient of friction and R=normal reaction

                                          R

                  

                           Fr            F              P

W=mg

At equilibrium, R = mg, this implies that

Fr = μmg                  2

        

μ = tanӨ                        3

Fr = RtanӨ                     4

If μ> 0, P< Fr + mgsinӨ      

 

ADVANTAGES OF FRICTION

  1. It makes walking and running possible
  1. It enables gripping of belt in machines possible
  2. It enables nails to stay in the wall when driven
  3. It stops tyre from slipping
  4. Enable cars to stop when breaks are applied
  5. Enables human to use mouse in surfing web

 

DISADVANTAGES OF FRICTION

  1. It causes wear and tear
  2. It reduces the efficiency of the machines
  3. It causes a lot of energy to be consumed by the machine
  4. It causes loss of resources

 

METHODS OF REDUCING FRICTION

  1. Lubricating surfaces with grease, oil etc.
  2. Using ball or roller on wheels
  3. Smoothing or polishing the surface
  4. Streamlining bodies

 

EVALUATION:    1. Define friction

  1. Mention four effect of friction
  2. State 2 ways of reducing friction
  3. metal block of mass 8kg lies on a rough horizontal platform. If the horizontal resistive force is 10N, find the coefficient of static friction (g=10m/s2)
  4. State two

                        (a) laws governing solid friction

                        (b) advantages of friction

                        (c) disadvantage of friction

  1. A body of weight 6N rest on a plane inclined at an angle of 300to the horizontal

          a. what force keeps it sliding down the plane?

          b. what is the coefficient of friction

       7. A body of mass 25kg, moving at 3m/s on a rough horizontal floor is brought to rest after sliding through a distance of 2.5m on the floor. Calculate the coefficient of sliding friction (g=10m/s2)

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively