Simple Machines V – Wheels and Axles and Gears
4th Grade
Daniel F. Fink, Lashonda Orrell, Lila Levendoski
References:
•
•
Columbus Public Schools SLC Guide
GK-12 Fellow Cheri Higgins
Benchmarks:
SLC 10: Explain the operation of a simple mechanical device
Objectives:
Students will learn the principles and uses of gears. They will note that gears can
be used to change the direction of motion or the speed of an object or the force/distance
through which an object turns. They will also come up with every day examples of
simple machines.
Materials:
•
•
WOW gear factory kits
Bicycle
Initial Demonstration:
Bring in a bicycle. Flip the bike over on its handlebars and seat. Turn the pedals,
ask the students “How does the bicycle work?”
Target Observations:
•
•
•
•
The pedals turn the large gear in the middle of the bike.
The chain is attached to the gear on the back of the bike and the gear in the middle
of the bike.
The chain causes the gear on the back of the bike to turn in the same direction as
the gear in the middle.
The gear on the back is attached to the rear axle which causes the rear wheel to
turn.
Target Model:
•
•
Gears can be linked by chains to help make things move in the same direction.
Gears that are directly connected will spin in the opposite direction as one
another.
Procedure:
1. Pass out to several different groups a set of gear factory kits.
2. Tell the groups to build a structure with the gears. The only rules are that:
a. Everyone in the group must place at lest one gear on the machine
b. When you rotate one gear, every other gear in the machine must also turn.
Vocabulary – driver gear, follower gear
What patterns can you deduce regarding how gears in series rotate?
3. Place three gears in a row on the factory kit. Make the first one big, the second
one small, and the third one medium.
4. Count the number of teeth in each of the gears of the gear factory kit. When the
gear on the left is rotated once, count the number of rotations of each of the other
gears and the direction that they rotate.
# teeth
rotations
Counter
Clockwise
clock-wise
Gear 1
Gear 2
Gear 3
Gear 4
5. Repeat with the multiplication gear kit [the gears are now all different sizes]
Target Observations:
•
•
Each time a gear drives another gear the direction of rotation is reversed.
The number of rotations that a gear will spin is dependant upon its size and
number of teeth and the size/number-of-teeth of the gear driving it.
Target Revised Model:
•
The number of rotations [how much work is done] by linked gears depends upon
the relative size of the gears [number of teeth]
Summary:
Gears have been demonstrated to the students. They have seen that two adjacent
gears will have opposite directions of rotation. They also have seen that the number of
times a gear goes around depends on how big the gears next to it are.