Procedure: Using the
May the Force be with You Worksheet each group uses
a spring scale to measure the force needed to balance the return spring at various
points along one arm of a salad tongs. They collect data showing the relationship
between force and distance, and graph the data to show the functional relationship.
These two variables are then multiplied to form a constant quantity called energy,
illustrating the Law of Conservation of Energy.
We have introduced the term mechanical advantage, but up to now have calculated it
only from distance measurements. To see what the “advantage” is, students now make
force (F) and distance (x) measurements at different locations along the arm. x is
always the distance from the fulcrum to the effort, which is supplied by the spring
scale. To make the distance measurements easier, it is convenient to tape a ruler
along the arm, making sure that the zero mark on the ruler is next to the fulcrum.
Based on what we have learned in “Visualizing Vectors,” the force measurements
should always be taken at a right angle to the arm, and approximately in mid-range
between open and closed positions. Using the template makes it easier to use the
same position each time.
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