Class: Junior Secondary School 2 (JSS 2 / JS2)
Term: Third Term
Week: 4 – 5
Age: 13 years
Duration: 45 minutes
Subject: Basic Science and Technology
Curriculum Theme: Basic Technology
Previous Lesson: Gears: Definition.
Topic: GEAR
Subject Matter: Gear ratio and speed: Function of lubricants in gears

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define gear ratio.
Calculate gear ratio and speed using given data.
Explain the functions of lubricants in gear systems.

Affective Domain:

Appreciate the importance of proper lubrication for machine longevity.
Show interest in how gears transmit motion and power.

Psychomotor Domain:

Identify different types of gears in simple machines.
Demonstrate how lubricants are applied to gear models.

Collaborate with peers in solving problems related to gear ratio and speed.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum
State Unified Scheme of Work
Basic Science and Technology for Junior Secondary Schools 2

Instructional Materials

The teacher will teach this lesson with the aid of:

Models of different gears (spur gear, helical gear).
A simple gear train system.
Charts illustrating gear ratios and lubrication points.
Samples of lubricants (e.g., engine oil, grease).

Rationale for the Lesson

Understanding gear ratio and speed helps pupils know how machines change speed and power. Knowing the function of lubricants is important for maintaining machines and extending their lifespan, which is a practical skill in daily life.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of simple machines and the concept of gears from previous lessons.

Lesson Content/Board Summary

GEAR RATIO AND SPEED: FUNCTION OF LUBRICANTS IN GEARS

Gear Ratio

Gear ratio is the relationship between the number of teeth on two meshing gears, or the ratio of their speeds. It tells us how much the speed or torque changes from one gear to another.

Formula for Gear Ratio (using number of teeth):

Gear Ratio (GR) = Number of teeth on Driven Gear (N_driven) / Number of teeth on Driving Gear (N_driving)

Gear Ratio (GR) = Speed of Driving Gear (S_driving) / Speed of Driven Gear (S_driven)

Where:

N_driven: Number of teeth on the gear being driven (output gear).
N_driving: Number of teeth on the gear that is driving (input gear).
S_driving: Speed of the driving gear (input speed), usually in revolutions per minute (RPM).
S_driven: Speed of the driven gear (output speed), usually in revolutions per minute (RPM).

Worked Example 1: Calculating Gear Ratio from Teeth

A driving gear has 20 teeth and a driven gear has 40 teeth. Calculate the gear ratio.

Step 1: Identify the number of teeth on the driving and driven gears.
N_driving = 20 teeth
N_driven = 40 teeth
Step 2: Apply the gear ratio formula.
GR = N_driven / N_driving
GR = 40 / 20
Step 3: Calculate the gear ratio.
GR = 2

Therefore, the gear ratio is 2:1.

Worked Example 2: Calculating Gear Ratio from Speed

A driving gear rotates at 100 RPM, and the driven gear rotates at 50 RPM. Calculate the gear ratio.

Step 1: Identify the speeds of the driving and driven gears.
S_driving = 100 RPM
S_driven = 50 RPM
Step 2: Apply the gear ratio formula.
GR = S_driving / S_driven
GR = 100 / 50
Step 3: Calculate the gear ratio.
GR = 2

Therefore, the gear ratio is 2:1.

Gear Speed

The speed of a gear system is inversely proportional to the number of teeth. A larger gear (more teeth) will rotate slower than a smaller gear (fewer teeth) when driven by it, and vice-versa.

Formula for Gear Speed:

Speed of Driven Gear (S_driven) = Speed of Driving Gear (S_driving) / Gear Ratio (GR)

S_driven = S_driving * (N_driving / N_driven)

Worked Example 3: Calculating Driven Gear Speed

A driving gear with 30 teeth rotates at 120 RPM. It drives a gear with 60 teeth. What is the speed of the driven gear?

Step 1: Calculate the gear ratio (GR).
N_driving = 30 teeth
N_driven = 60 teeth
GR = N_driven / N_driving = 60 / 30 = 2
Step 2: Identify the speed of the driving gear.
S_driving = 120 RPM
Step 3: Apply the formula for the speed of the driven gear.
S_driven = S_driving / GR
S_driven = 120 RPM / 2
Step 4: Calculate the speed of the driven gear.
S_driven = 60 RPM

The speed of the driven gear is 60 RPM.

Function of Lubricants in Gears

Lubricants are substances, usually liquids or semi-solids (like oil or grease), applied between moving parts to reduce friction and wear.

The following are the functions of lubricants in gears:

Reduce Friction: Lubricants create a thin film between the meshing gear teeth, preventing direct metal-to-metal contact and reducing friction.
Reduce Wear: By reducing friction, lubricants minimize the wearing out of gear teeth surfaces, extending the lifespan of the gears.
Prevent Corrosion: Lubricants often contain additives that protect metal surfaces from rust and corrosion, especially in moist or harsh environments.
Dissipate Heat: As gears operate, friction generates heat. Lubricants help to absorb and carry away this heat, preventing overheating and damage to the gears.
Reduce Noise and Vibration: The lubricating film cushions the impact between gear teeth, leading to smoother operation and reduced noise and vibration.

Types of Lubricants for Gears:

Oils: Commonly used in enclosed gearboxes, available in various viscosities.
Grease: A semi-solid lubricant, suitable for open gears or applications where oil might leak out.

Proper lubrication is essential for the efficient and long-lasting operation of gear systems.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils, reviews the previous lesson on simple machines, and introduces the topic of “Gear Ratio and Speed: Function of Lubricants in Gears” by asking what gears are used for.
Pupils’ Activity: Pupils respond to questions and listen attentively to the introduction of the new topic.
Learning Point: Pupils recall previous knowledge and are prepared for the new lesson.

Step 2: Explanation of Gear Ratio

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher defines gear ratio, explains the formulas for calculating it using the number of teeth and speed, and works through Example 1 from the board summary.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the definition and basic calculation of gear ratio.

Step 3: Calculation of Gear Ratio

Time: 10 minutes
Teaching Skill: Guided Practice
Teacher’s Activity: The teacher guides pupils through Example 2 on calculating gear ratio from speeds and provides a similar problem for pupils to solve individually or in pairs.
Pupils’ Activity: Pupils participate in solving the example and attempt the practice problem.
Learning Point: Pupils practice and improve their ability to calculate gear ratio.

Step 4: Explanation of Gear Speed

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the relationship between gear size, gear ratio, and speed, then introduces the formula for calculating the speed of the driven gear and works through Example 3.
Pupils’ Activity: Pupils listen, observe the demonstration, and take notes.
Learning Point: Pupils understand how gear ratio affects the speed of gears.

Step 5: Function of Lubricants

Time: 7 minutes
Teaching Skill: Explanation/Discussion
Teacher’s Activity: The teacher defines lubricants and explains their main functions in gears, such as reducing friction, wear, and corrosion, and dissipating heat.
Pupils’ Activity: Pupils listen and contribute to the discussion by sharing their ideas on why lubrication is important.
Learning Point: Pupils understand the critical roles lubricants play in gear systems.

Step 6: Types and Application of Lubricants

Time: 3 minutes
Teaching Skill: Demonstration
Teacher’s Activity: The teacher shows samples of different lubricants (oil, grease) and briefly discusses their appropriate application areas on gear models.
Pupils’ Activity: Pupils observe the samples and demonstrations.
Learning Point: Pupils identify common types of lubricants and understand their practical use.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define gear ratio.
A driving gear with 25 teeth rotates at 150 RPM and drives a gear with 50 teeth. Calculate the gear ratio and the speed of the driven gear.
List three functions of lubricants in gear systems.
Mention two types of lubricants used for gears.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson on gear ratio, speed, and the functions of lubricants. The teacher then gives homework: research other types of gears and their uses.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils consolidate their learning and are assigned further study.

Lesson Keywords

Gear – A rotating machine part having cut teeth which mesh with another toothed part to transmit torque.
Gear Ratio – The ratio of the number of teeth of two meshing gears, or their speeds.
Speed – The rate at which an object or gear rotates, often measured in Revolutions Per Minute (RPM).
Lubricant – A substance introduced between two moving surfaces to reduce friction and wear.
Friction – The resistance that one surface or object encounters when moving over another.
Driven Gear – The gear that receives motion and power from another gear.
Driving Gear – The gear that initiates motion and transmits power to another gear.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide more complex gear ratio problems involving multiple gears in a train. For pupils needing more support, the teacher can offer simplified examples and one-on-one guidance, emphasizing the visual aids and practical demonstrations.

Note for teachers using this lesson plan

Ensure that pupils have a clear understanding of the terms ‘driving gear’ and ‘driven gear’. Use physical gear models to demonstrate how changing the number of teeth affects speed and direction. Emphasize the practical importance of lubrication in everyday machinery. Encourage pupils to draw and label simple gear systems.