1. Gear Ratios What are gears ratios? Calculating SR of gear systems
Lesson 34 - Gear Ratios
Gear Ratios
What are gears ratios?
Calculating SR of gear systems

2. Gears Recap
Big Idea
If we use a gear to “reduce” the output speed of a system, we will end up “multiplying” the output force
Visa Versa
If we use a gear to “multiply” the output speed of a system, we will end up “reducing” the output force.

3. Gears Recap
The DRIVER GEAR is the first gear in the system and is the gear that has the energy source coupled to it
The DRIVER GEAR moves the system
DRIVER GEAR
Please draw a picture of a bike in your notes and label the “driver” and “follower” gears

4. Gears Recap
The FOLLOWER GEAR is the second gear in the system and is the gear that receives the energy from the driving gear
The FOLLOWER GEAR is moved in the system
FOLLOWER GEAR

5. Reducing vs. Multiplying
We base the terms…
MULTIPLYING or
REDUCING
gear systems based on the NUMBER of REVOLUTIONS of the FOLLOWER GEAR

6. Textbook Reading
We are going to do a quick individual reading from the Science Focus Textbook
Please read the pages listed… while you are reading be sure to look for the formula that calculates the SPEED RATIO
Pages

7. Speed Ratio = # of Driver Teeth . # of Follower Teeth
Speed Ratio Formula
Formula for Speed Ratio of a Gear System…
Speed Ratio = # of Driver Teeth .
# of Follower Teeth
Remember though, the ratio must be reversed to indicate the number of revolutions each gear completes… the first number always represents the # of revolutions the Driver Gear completes

8. Calculating Ratios Calculating a Ratio
Speed Ratio = # of Driver Teeth .
# of Follower Teeth
SR Fraction = _____ Gear Ratio ____ : ____
From your formula, you end up with a SR fraction… you must simplify this fraction. DO NOT DIVIDE!!!
Top Number = the size of Driver Gear
1st # = Number of spins the driver gear makes
2nd # = Number of spins the Follower gear makes
Bottom Number = the size of Follower Gear
Between your fraction and ratio… the numbers switch

9. Example Question Calculate the Speed Ratio of the Gear System…
Follower Gear
Driver Gear

10. Example Answer Start with the Formula 1 spins to 2
SR = # of Driver Teeth
# of Follower Teeth
SR = 60 30
SR = or we write it… 1
1 spins to 2
GR = 1 : 2
Is this a Multiplying or Reducing gear system?

11. Example Question Calculate the Speed Ratio of the Gear System…
Driver Gear
Follower Gear

12. Example Answer Start with the Formula 3 spins to 1
SR = # of Driver Teeth
# of Follower Teeth
SR = 25 75
SR = or we write it… 3
3 spins to 1
GR = 3 : 1
Is this a Multiplying or Reducing gear system?

13. Example Question Calculate the Speed Ratio of the Gear System…
Driver Gear
Follower Gear

14. Example Answer Start with the Formula 4 spins to 1
SR = # of Driver Teeth
# of Follower Teeth
SR = 20 80
SR = or we write it…
4 spins to 1
GR = 4 : 1
Is this a Multiplying or Reducing gear system?

15. Your Assignment!!! Due for Tomorrow
You are being given a short worksheet that is deals with everything that we have been working on in terms of gears
We will go over this worksheet in class tomorrow.
BE SURE TO SHOW ALL OF YOUR WORK WHEN YOU ARE COMPLETING THE CALCULATIONS
Ask for help if you need it