Introducing Machines That Help
MOVIE 1 shows Earl Carlyon setting the stage for work
on the Machines That Help (MTH) task. MOVIE 2 shows
science teacher Mike Ryan reviewing the introduction
to MTH that he conducted a day earlier with his class.
He then gets groups to work on initial ideas, and assigns
as homework the task of sketching these ideas for discussion the next day.
The essential MTH challenge involves a situation where
only a small Applied Force is all that is available
to lift a heavy can of food. The small AF represents
the challenge's main constraint, and is enforced by
requiring that students not touch their machine directly.
They can do it only via a single strand of cotton thread
that you as teacher supply to students. Students learn
about a variety of simple machines that can be combined
to take the small AF, multiply it (with the tradeoff
of the AP traveling a greater distance), and then raise
As you will see in ensuing MTH movies, not all students
grasp that the string must be attached on the Applied
Force side of their mechanisms. Nor do they immediately
see that different machines provide differing factors
of Mechanical Advantage (MA multiplies the AP; it is
not added to AP). They also do not recognize that with
machines: tradeoffs are always involved. Finally, they
do not all know that some mechanisms (like a simple
pulley) offer no MA at all. All of these misconceptions
can be deeply embedded in students' solutions to design
problems and explanations for their design choices.
You will need to address these misconceptions at some
point in the unit, or later on in the year.