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Simple Machines: Gears, Velocity Ratios and Mechanical Advantage

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

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Simple Machines: Gears, Velocity Ratios and Mechanical Advantage

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  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.

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