Look
around at the links, levers, cams, pulleys and gears that are
used in everyday situations and try to think of new ideas for
mechanical toys. Look at the web-sites that show 'automata'
and analyse why these toys work as they do.
Start
by looking at the three 'orders' of levers. The first class
~ Number 1 is a simple see-saw or scissors. Notice
how the effort needed to move the load is reversed in the direction
it acts on the load. Look at the other two classes and see
if the same happens with those. Class 2 is seen in the example
of the wheelbarrow and the class 3 lever is seen in things such
as tweezers and fishing rods. This last class is an inefficient
system as the load is further from the fulcrum than the effort.
Class 1
Class 2
Class 3
~
CAMS
~ Making
things move 'up and down'
or from
'side to side'.
Cams
are used
most easily to give effective toys.
~
GEARS~
Changing
the speed of things ~ Reversing the direction
of motion
The
most important feature of understanding gears in KS3 and KS4 projects
is to be able to predict how fast an output gear wheel is going
to be turning from a particular input gear speed.
Each time one tooth of a gear
wheel moves it passes on the same movement to the interlocking
gear. You would expect two gear wheels each with 100 teeth
to rotate at exactly the same speed.....wouldn't you ... If one
wheel had twice the number of teeth that the input gear had
then you might expect it to take longer to turn round.
