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One of the main reasons for having gears
and pulleys other than to change the way in which things move is to change the speed at
which they move. One of the wheels is always connected to a power source such as a motor
and this is referred to as the DRIVER. The
one which is connected to the driver, either by a belt or teeth is called the DRIVEN.
Once we know which is the driver and which is the driven and if we know how big the
wheels are (if it is a pulley) or how many teeth they have ( if they are gears) we can
begin to work out the GEAR RATIO or the VELOCITY RATIO.
Look at the formula :
DRIVEN (size of wheel for a pulley, No. of teeth
for a gear)
VELOCITY RATIO =--------
DRIVER (size of wheel for a pulley, No. of teeth
for a gear)
DRIVEN
This formula can be shortened to VR= --------
DRIVER
When you make the calculation you are left with a fraction which is then converted
into a ratio.
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