Simple machines provide users with a benefit called
Mechanical Advantage (MA), but only with a Tradeoff
or off-setting cost. Some machines offer the advantage
of multiplying the Applied Force with a Tradeoff that
the AF must travel a greater distance. Others multiply
the distance the AP travels, but only with a proportional
reduction in the AF. Making these ideas real and memorable
to students are two goals of science teacher Earl Carlyon's
demonstration of a first-class lever.
From your standpoint as a teacher, you might evaluate
how well MOVIE 1's demo seems to go. Listen carefully
to the questions Earl embeds in the demo that addresses
student misconceptions about lifting forces and gravity.
Note the misconceptions that appear in students' statements
(e.g., at least one student thinks that if a person
tries to lift something but is not successful, then
no force has been applied), and how Earl addresses each.
Look also for how Earl choreographs his demo with safety