# Lesson Notes By Weeks and Term - Senior Secondary 1

Friction

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
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

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

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