1. Simple Machines: Gears, Velocity Ratios and Mechanical Advantage

2. What is a simple machine?  A device which uses basic mechanisms to make work easier for the user.  Example: Lifting a heavy box with a rope and pulley system  Simple machines are found in many transportation devices such as the following:  Cars  Bicycles  Trains

3. What are gears and why are they so useful?  Gears are toothed wheels which interlock to form simple machines.  The tighter the joint, the less chance of slipping  Gears range in size but the important number is how many teeth a gear has.

4. What is a gear ratio?  A gear ratio is the ratio between the driver gear (the one being powered) and the driven gear (the one connected to the driver)  Gear Ratios are expressed as fractions and can be written a number of ways.  1 to 3  1/3  1:3  Always remember that the driven gear will turn in the opposite direction of the driver gear

5. What is a pulley?  A wheel with a grove carved around its circumference in which a rope or belt is placed to drive the wheel.  Pulleys are used in a number of applications including:  Elevators  Cranes  Automobiles

6. A Pulley System

7. Drawbacks of Pulleys  Pulleys work great as long as the belt which connects them is tight and both pulleys are aligned.  Pulleys tend to slip when too much strain is placed on the system.

8. How do I calculate my gear ratio?  A simple equation is used to find the ratio of your gearing system  Number of Teeth on the Driven Gear / Number of Teeth on the Driver Gear.  Size of the driver pulley/ Size of the driven pulley

9. What is Velocity Ratio (VR)?  When calculating for velocity or speed, it is best to have a ratio in which the driver gear is larger than the driven gear.  For maximum speed you should always have a larger driver gear/pulley paired with a smaller driven gear/pulley.

10. What is Mechanical Advantage (MA)?  Reciprocal of velocity ratio.  Mechanical advantage describes how much work can be done based on the input.  If my system required me to apply 50 pounds of force into the system to lift 100 pounds of weight, I have used MA.

11. So which do I want?  Higher velocity ratios are better when working on straight and level surfaces which are smooth.  Always remember that with a high VR your system will have very low power.  Higher mechanical advantage systems are better with inclines surfaces that are bumpy.  With a high MA your system will produce more power, but will move slower.