Lesson Plan Industry Sector
Transportation

**Gears (updated) by Beau Sunahara

Lesson Plan Overview / Details

In this lesson, students will count teeth on gears and calculate the gear ratio between two gears; compare and contrast drive and driven gears; accurately describe the direction gears move when linked together; and do individual and group work.

1 Class period
55 Minutes

Objectives and Goals

• Students will be able to describe which direction various gears spins when linked together
• Students will be able to calculate gear ratios by counting teeth on two gears
• Students will be able to calculate gear ratios of input ratio vs. output ratio
• Students will be able to calculate final drive ratio

Gears Vocabulary

Bevel gear
A gear wheel meshed with another so that their shafts are at an angle less than180 degrees
Drive gear
Power is coming into the drive gear
Driven gear
Connected to a drive gear power is leaving the driven gear
Gear ratio
The number of revolutions a drive gear must turn before the driven gear completes one revolution
Helical gear
A gear with its teeth machined at an angle to the centerline of the gear shaft (angled teeth gears)
Spur gear
A gear wheel having radial teeth parallel to the axle. (straight teeth gears)

NATEF Standards

• Manual Drive Train and Axles: Task A-4 Locate and interpret vehicle and major component identification numbers.

Activities in this Lesson

• Bicycle discussion - Hooks / Set

After students are seated, I ask if they have ever ridden a multi-geared bicycle before. What do they do when they ride up hill? What do they do when they ride down hill? (If students have never ridden a multi-geared bike, I ask how it feels when they ride uphill.)

Students usually answer, "Change gears!"  Teacher will try to ascertain previous knowledge of students by clarifying which direction would they shift gears (high or low).

Teacher will ask students to predict whether or not they could start pedaling their bike in the highest gear.

After a short discussion, we talk about the day's objectives so students know what we are doing for the day.

• By dividing the number of teeth on the driven gear by the number of teeth on the drive gear, we get our gear ratios between two gears.  If a driven gear has 24 teeth and a drive gear has 12 teeth, the resulting calculation will be (24 / 12 = 2) which gives us a gear ratio of 2 : 1.

Students must also describe which direction each gear will turn if the first gear (yellow) is being spun clockwise.

Teacher will explain as the first gear (yellow gear) rotates clockwise, the second gear (red gear) will rotate in the opposite direction (counter-clockwise) while the last gear (blue gear) will rotate in a clockwise motion.

Teacher will show the animation of two gears spinning while marked with a white dot.

The teacher will ask for questions at the end of the lecture to clarify explanations.

Students will take Cornell-style notes during lecture.

• Calculating ratios - Demo / Modeling

By dividing the number of teeth on the driven gear by the number of teeth on the drive gear we get our gear ratios between two gears.  If a driven gear has 24 teeth and a drive gear has 12 teeth the resulting calculation will be (24 / 12 = 2) which gives us a gear ratio of 2 : 1

Students must also describe which dirction each gear will turn if the first gear (yellow) is being spun clock-wise.

Teacher will explain as the first gear (yellow gear) rotates clockwise the second gear (red gear) will rotate in the opposite direction (counter-clock wise) while the last gear (blue gear) will rotate in a clock wise motion.

Teacher will show the animation of two gears spinning while marked with a white dot.

The teacher will ask for questions at the end of the lecture to clarify explanations.

Students will take Cornell style notes during lectures.

• Students in groups of two can identify different types of gears.

Teacher will pass out spur gears, helical gears, bevel gears, and hypoid gears.

The new gears (bevel and hypoid) will proceed into a new discussion on different types of gears for differential.

• Now students will individually calculate a final ratio from two different gear ratios. After this exercise, students will now predict how to calculate final drive ratio.

The teacher will give a differential gear ratio of 3 : 1 and students must calculate final drive ratios.

The teacher will give the formula differential gear ratio X current gear selected = final drive ratio.

The teacher will write on the board differential gear ratio 3:1, 1st gear 3:1, 2nd gear 2:1, direct drive 1:1, and overdrive .75:1 .

Some calculators are provided, although students may use their own calculators.

• Closure - Closure

At the end of the lesson, the teacher will collect the final drive work sheets and ask for any final questions from the students.

Assessment

Assessment Types:
Demonstrations, Observations, work sheets

During group work the teacher will walk around observing group work on identification of the various gears.

During individual work the teacher will walk around checking for understanding as students calculate ratios by counting the teeth on the gears.

Students will turn in Final drive work sheet