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

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## Simple Machines: Gears, Velocity Ratios and Mechanical

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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. – PowerPoint PPT presentation

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Title: Simple Machines: Gears, Velocity Ratios and Mechanical

1
Simple Machines Gears, Velocity Ratios and
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
• 13
• 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
• 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
• 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.