Simple Machines: Simple Machines: Gears, Velocity Ratios Gears, Velocity Ratios

and Mechanical and Mechanical AdvantageAdvantage

What is a simple What is a simple machine?machine?

A device which uses A device which uses basic mechanisms to basic mechanisms to make work easier for the make work easier for the user.user. Example: Lifting a heavy Example: Lifting a heavy

box with a rope and pulley box with a rope and pulley systemsystem

Simple machines are Simple machines are found in many found in many transportation devices transportation devices such as the following:such as the following: CarsCars BicyclesBicycles TrainsTrains

What are gears and why What are gears and why are they so useful?are they so useful?

Gears are toothed Gears are toothed wheels which interlock wheels which interlock to form simple to form simple machines.machines. The tighter the joint, The tighter the joint,

the less chance of the less chance of slippingslipping

Gears range in size Gears range in size but the important but the important number is how many number is how many teeth a gear has.teeth a gear has.

What is a gear ratio?What is a gear ratio?

A gear ratio is the ratio between the driver gear A gear ratio is the ratio between the driver gear (the one being powered) and the driven gear (the one being powered) and the driven gear (the one connected to the driver)(the one connected to the driver) Gear Ratios are expressed as fractions and can be Gear Ratios are expressed as fractions and can be

written a number of ways.written a number of ways. 1 to 31 to 3 1/31/3 1:31:3

Always remember that the driven gear will turn in Always remember that the driven gear will turn in the opposite direction of the driver gearthe opposite direction of the driver gear

What is a pulley?What is a pulley?

A wheel with a grove carved around its A wheel with a grove carved around its circumference in which a rope or belt is circumference in which a rope or belt is placed to drive the wheel.placed to drive the wheel. Pulleys are used in a number of applications Pulleys are used in a number of applications

including:including: ElevatorsElevators CranesCranes AutomobilesAutomobiles

A Pulley SystemA Pulley System

Drawbacks of PulleysDrawbacks of Pulleys Pulleys work great as long as the belt which Pulleys work great as long as the belt which

connects them is tight and both pulleys are connects them is tight and both pulleys are aligned.aligned. Pulleys tend to slip when too much strain is placed Pulleys tend to slip when too much strain is placed

on the system.on the system.

How do I calculate my How do I calculate my gear ratio?gear ratio?

A simple equation is used to find the ratio of your gearing A simple equation is used to find the ratio of your gearing systemsystem Number of Teeth on the Driven Gear / Number of Teeth on Number of Teeth on the Driven Gear / Number of Teeth on

the Driver Gear.the Driver Gear. Size of the driver pulley/ Size of the driven pulleySize of the driver pulley/ Size of the driven pulley

What is Velocity Ratio (VR)?What is Velocity Ratio (VR)?

When calculating for velocity or speed, it is When calculating for velocity or speed, it is best to have a ratio in which the driver gear is best to have a ratio in which the driver gear is larger than the driven gear.larger than the driven gear. For maximum speed you should always have a For maximum speed you should always have a

larger driver gear/pulley paired with a smaller larger driver gear/pulley paired with a smaller driven gear/pulley.driven gear/pulley.

What is Mechanical What is Mechanical Advantage (MA)?Advantage (MA)? Reciprocal of velocity Reciprocal of velocity

ratio.ratio. Mechanical advantage Mechanical advantage

describes how much describes how much work can be done based work can be done based on the input.on the input.

If my system required me If my system required me to apply 50 pounds of to apply 50 pounds of force into the system to force into the system to lift 100 pounds of weight, lift 100 pounds of weight, I have used MA.I have used MA.

So which do I want?So which do I want?

Higher velocity ratios are better when working Higher velocity ratios are better when working on straight and level surfaces which are on straight and level surfaces which are smooth.smooth. Always remember that with a high VR your system Always remember that with a high VR your system

will have very low power.will have very low power.

Higher mechanical advantage systems are Higher mechanical advantage systems are better with inclines surfaces that are bumpy.better with inclines surfaces that are bumpy. With a high MA your system will produce more With a high MA your system will produce more

power, but will move slower.power, but will move slower.