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# Simple Machines: Gears, Velocity Ratios and Mechanical Advantage PowerPoint PPT Presentation

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

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## Simple Machines: Gears, Velocity Ratios and Mechanical Advantage

### 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

### 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.

### 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

### 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

### 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.

### 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

### 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.

### 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.

### 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.