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 the Load.

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.