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1. What kind of gears does the K’NEX Car
Window use: spur, crown, rack and pinion,
worm or sprocket gears?
2.
a.
Lower the Car Window all the way and then
turn the crank one full turn to raise the
window.When you turn the crank one full turn,
how much does the blue Gear turn?
[Note: Be
careful not to overwind the window or the blue Rod
will pop off!]
How much does the yellow Gear
turn? What is the Mechanical Advantage for this
gear system?
b.
Now turn the crank one full turn again and
watch the blue Gear on the top axle (the Rod
with the yellow Gear). How much of a turn
does it make? How does this compare to the
yellow Gear?
c.
Turn the crank fully again and watch the green
Gear. How much does it turn? What is the ratio
between the blue and green Gears? What is
the MA?
d.
Why does the Car Window have this
arrangement of Gears? What would happen
to the Car Window if the arrangement was
reversed? Explain.
3 The K’NEX Car Window uses circular motion
to make the window go up and down.Turn the
handle and observe how the Gears and the arm
that holds the window work together.Would
rack and pinion gears work well to raise and
lower a car window? Make a drawing to show
how it might work.Then, build a K’NEX car
window using rack and pinion gears.
1
1. The Car Window uses two pairs of spur gears.
Note that the Gears in each pair lie in the same
plane.
2
a.
Since this blue Gear is on the same axle as
the crank, it turns once for one turn of the
crank.The yellow Gear makes a little less than
one-half turn.The Mechanical Advantage for
these Gears is 2.43.
b.
The blue Gear on the top axle turns a little
less than half a turn when the crank turns a full
turn. It turns the same amount as the yellow
Gear. Help students see that even though the
blue and yellow Gears are different sizes, they
turn the same amount because they are on the
same axle.The gear ratio is not a factor.
c.
The green Gear only turns a very short dis-
tance for a full turn of the crank.The gear ratio
is 6:1.The MA is 6. In this case, the small Gear
turns without needing to use a lot of force, but
the big Gear can only cover a short distance.
This works out fine since the Car Window only
has a short distance to move.
d.
The gear ratio and MA greatly affect how the
Gears work together. Help students see that
the combination of all these Gears makes it
possible for you to move the window just a
little without having to be very precise in your
turning action or providing a lot of effort. If the
gear configuration was reversed, it would take
more effort to turn the crank and the window
would move so quickly that you would have to
take great care when turning or you could
damage the window.
3. When designing a car window using rack and
pinion gears, students will probably design a
vertical rack that pushes the window up.As
they build, they might discover advantages or
disadvantages to using rack and pinion gears.
They will need to consider where the window
crank will be positioned on the door
(preferably in a place where it could easily be
reached!) and where the rack will move as the
window goes up (possibly under the window or
along the side).
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ANSWERS
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Summary of Contents for Education Simple Machines Deluxe GEARS
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