Learning About Gears - Thames & Kosmos AIR Plus Water Power Experiment Manual

Learning about Gears

Gears are wheels with teeth on them. The teeth, or cogs, of one gear mesh with the teeth of another gear to
transmit force between them. A combination of two or more gears is called a transmission, or gear train. You can
see transmissions with meshing gears inside old toys or old clocks. Gearboxes can be found inside the transmis-
sion system of cars, which combine meshing gears of different sizes. This allows the car's driver to easily change
between different speeds.
Do you know how gears work? You can learn how gears work and why they are useful by reading this manual and
building the models in this kit that use gears. The building blocks in this kit were designed based on the number
ten and its multiples, including the size of the components, the distance between the holes, or the unique gears.
This makes it easy to both assemble the gears and also conveniently calculate the gear ratio or change the ro-
tary speed. Different from other gear designs that use the number seven or eight as their fundamental number,
these gears were created to be perfect for teaching science to kids because they are easy to assemble and
they make it easy to calculate gear ratios (explained below).
We recommend a gradual learning process using these gears, which begins with very basic assemblies to un-
derstand how each of the components fit together. After you build all of the models in this instruction book
and understand how to use gear trains, you can put your unlimited creativity to work and design vehicles and
machines on your own. Let your imagination guide you!
Now let's look closely at gears and how we use them. Find the gears in this kit. The wheels which have many
tooth-shaped objects sticking out of their edges are gears. Two gears can mesh with each other using the teeth
on the edges. When one gear rotates, the other one will be driven to rotate as well. The intermeshing teeth of
the two gears transmit torque (turning force) and rotation.
A simple gear train uses two gears with the
same or different sizes. If one of these gears
is attached to a motor or a crank, it takes the
role of the driver gear. The gear that is turned by
the driver gear is called the driven gear. Gears of
different sizes are used to increase or decrease
the speed or the power of rotary motion. The
relationship between the number of teeth on
intermeshing gears is called the gear ratio (or
speed ratio). The gear ratio reveals the change
in speed or power from one gear to the other.
Illustration of gear ratio calculation
GEAR
Fig. B
3
| AIR+WATER power
Fig. A
The intermeshing of gears
can effectively transmit
force to cause rotation. The
red circle represents the ac-
tual diameter of the trans-
mission, which is called the
pitch diameter. The special
shape of the teeth allows
for smooth intermeshing
and transmits power along
the pitch.
40 teeth
Driven gear
Velocity
Number teeth driven gear
=
ratio
Number teeth driver gear
40 1
= = (2:1)
20 2
20 teeth
Driver gear