Teacher Information: Using Gear Mechanisms
Mottisfont’s good supply of water supported the use of gear mechanisms across the ages. There
is evidence of old watermills in the Abbey Stream, and in more recent times, water from the font
was used to drive a spit roast in the kitchen.
People use mechanisms in everyday life so that they need less energy to perform a task e.g.
cycling faster/cycling uphill.
Please note: the café where the spit is located is often busy so you will need to prearrange a
suitable time for the children to have access. Please make sure you do this when you book/carry
out your pre-visit.
Curriculum link: Forces Year 5. Learning Objectives/Success Criteria: I understand that some
mechanisms allow a smaller force to have a greater effect. I can recognise that gears allow a
smaller force to have a greater effect.
Resources:
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Pictures of meat cooking on a range comparable to the one at Mottisfont
4 calculators
4 stopwatches
4 pencils/tables
4 clipboards (available on loan from Mottisfont)
Activity
1. Prior to your visit, discuss how and why gears are really useful in everyday life. Try out
different gearing construction sets and look at familiar mechanical devices with gears. Talk
about water wheels, milling gear and kitchen spit roaster in preparation for your visit.
2. As you walk into the property and cross the bridge, point out the Abbey Stream, site of the
old watermill, and explain the significance of the water source – the font.
3. Walk up to the house and stop just inside at the water wheel. Explain that even though the
mill is no longer there, the house used water to power the spit in the kitchen.
4. Show the group of children the rotating spit in the kitchen. Show pictures of it in use in the
past and discuss why the meat had to be rotated. Why might the cook want to speed/slow
down the rotation?
5. Explain that the water from the font is channelled to the house and the force of the water is
used to turn a water wheel which turns a series of cogs and gears which ultimately turns the
spit for the range. Show the children the waterwheel and cogs/gears mechanism that turns
the spit. Explain that the mechanism enables the spit to be rotated using the force of the
water instead of human power (i.e. an energy saving device).
6. INVESTIGATION: compare the speed of the gears in each section of the spit mechanism.
Children could record each section 3 times and find the average. To count the ‘turns’
choose a marking already visible on the cogs.
Health and safety: warn children to beware when observing the hook on the spit because
it rotates.
7. Children to work in groups. Assign roles – recorder, measurer, equipment manager,
reporter. Give the children the worksheet table to complete.
1 Equipment manager collects stopwatch and starts/stops watch.
2 Measurer to count the number of times the cog turns in one minute.
3 Recorder to write down number of turns.
4 Reporter to share results with class group at the end.
What do they notice about the number of turns of the spit in comparison the number of
turns of the water wheel?
Plenary: share the results of all the groups. Encourage the children to use comparative language.
Summarise by explaining that the arrangement of the cogs and gears means that the same force
of water is used to roughly double the power i.e. the use of the gears has allowed a smaller force
to have a greater effect and the gears have enabled the mechanism to change direction. (There
may need to be a discussion on the reliability of the measurements!)
Recording table (available as a downloadable worksheet)
Water wheel
1st count
2nd count
3rd count
Average
number of
turns
Gear section Gear section Spit hook
on right
turning
Additional Information for teachers: gears
Gears are wheels with teeth that slot together. When one gear is turned the other one turns as
well. If the gears are of different sizes, they can be used to increase the power of a turning force.
The smaller wheel turns more quickly but with less force, while the bigger one turns more slowly
with more force. Cars and bicycles use gears to achieve amazing speeds our bodies could never
match without help. (Reference: http://www.dkfindout.com/uk/science/simple-machines/gears/)
The larger wheel has four times as many teeth as the smaller wheel. This means that every time
the larger wheel turns once, the smaller one turns four times.
It takes four times as much force to turn the large wheel around once as it does to turn the small
wheel around once.
For example bicycle gears:
Gears on a bicycle are usually linked by a chain but they work the same way as gears that are
touching. The chain transfers the turning force from the pedals, to the gears to turn the wheels to
make the bicycle move along. The chain can be moved to gears of different sizes either to go
faster e.g. increase the speed for racing or decrease the force needed, e.g. to climb up hills.
You can have any number of gears connected together and they can be in different shapes and
sizes. Each time you pass power from one gear wheel to another, you can do one of three things:
increase speed, increase force, or change direction.
1. Increase speed: if you connect two gears together and the first one has more teeth than the
second one (generally that means it's a bigger-sized wheel), the second one has to turn
round much faster to keep up. So this arrangement means the second wheel turns faster
than the first one but with less force.
2. Increase force: if the second wheel in a pair of gears has more teeth than the first one (that
is, if it's a larger wheel), it turns slower than the first one but with more force.
3. Change direction: when two gears mesh together, the second one always turns in the
opposite direction. So if the first one turns clockwise, the second one must turn counter
clockwise. You can also use specially shaped gears to make the power of a machine turn
through an angle. In a car, for example, the differential (a gearbox in the middle of the rear
axle of a rear-wheel drive car) uses a cone-shaped bevel gear to turn the driveshaft's power
through 90 degrees and turn the back wheels.