Lesson Notes By Weeks and Term - Junior Secondary School 2

SUBJECT:  BASIC TECHNOLOGY       

CLASS:  JSS2

DATE:

TERM: 3RD TERM

REFERENCE MATERIALS 

• MELROSE, Basic Science and Technology Book 2
• NERDC, Basic Technology for JSS, Book 2

WEEK FIVE

TOPIC: GEARS (CONTD.)                                                                

CONTENT 

• Gear Ratio
• Gear Speed

GEAR RATIO

Gear ratio is defined as the ratio of number of teeth of output to input gear or input speed relative to output speed. It is calculated by dividing the number of teeth on the driven gear by the number of teeth on the driver gear.

Gear ratio= Number of teeth on the driven gear

Example: Calculate the gear ratio if a gear with 15 teeth is used to drive a gear with 30 teeth.

Gear ratio= Number of teeth on the driven gear= 30/15= 2/1

Gear ratio= 2:1

Ratio of a Series of Gears

When power flows through a series of gears, the ratio can be calculated in a similar manner. For example, if a 20-tooth driver gear drives a 24-tooth cluster gear, and the second speed cluster gear has 16 teeth driving a 20-tooth second speed driven gear, this could be calculated as follows:

Driven/Driver x Driven/Driver= 24/20 x 20/16= 1:5:1

GEAR SPEED

Gear speed is a measurement of how quickly a gear spins, often in a relation to the rotations of other gears. The speed of rotation of a gear is directly proportional to the number of teeth of the gear. For example, the speed of a 5-tooth gear will be twice the speed of a 10-tooth gear.

Example: A gear has 20 teeth. Its speed of rotation is 10 rpm. The gear drives another gear with 10 teeth. Determine the speed of the 10-tooth gear.

Solution

20 teeth x 10 rpm= 10 teeth x X rpm 

X rpm= 20 teeth x 10 rpm/10 teeth

X rpm= 20 rpm 

EVALUATION QUESTIONS

1. What is gear ratio?
2. Explain gear speed

GENERAL EVALUATION

1. Calculate the gear ratio if a gear with 20 teeth is used to drive a gear with 40 teeth.
2. A gear has 10 teeth. Its speed of rotation is 20rpm. The gear drives another gear with 15 teeth. Determine the speed of the 15-tooth gear.

READING ASSIGNMENT

Read about hydraulics and pneumatic machines (NERDC Basic Tech. for JSS3 page 170-180)

WEEKEND ASSIGNMENT

1. Calculate the gear ratio if a gear with 12 teeth is used to drive a gear with 16 teeth. (a) 4:3 (b) 3:4 (c) 2:1 (d) 1:2
2. A gear has 15 teeth. Its speed of rotation is 25rpm. The gear drives another gear with 25 teeth. Determine the speed of the 25-tooth gear. (a) 10rpm (b) 20rpm (c) 15rpm (d) 30rpm
3. The ratio of input speed relative to output speed is…… (a) gear speed (b) gear ratio 

(c) gear decimal (d) gear fraction 

1. The speed of rotation of a gear is ……………. to the number of teeth of the gear (a) equal (b) unequal (c) inversely proportional (d) directly proportional
2. ………. is a measurement of how quickly a gear spins (a) gear ratio (b) gear speed

(c) gear decimal (d) gear fraction 

THEORY

1. Explain (a) Gear Speed (b) Gear Ratio
2. (a) A gear has 32 teeth. Its speed of rotation is 4rpm. The gear drives another gear with 8 teeth. Determine the speed of the 8-tooth gear.