Teaching Notes

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SAFETY PRECAUTIONS: Close supervision is
needed to prevent injury or damage to equipment and
surrounding items when students set themselves into
motion by pushing off from the wall.
You may wish to emphasize that the reaction forces
which we “feel” throughout a day are not limited to
the reaction forces felt while running or walking, but
include the reaction force which occurs whenever we
touch something.
You may wish to do Activity 5 A, Using a Bathroom
Scale to Measure Forces, following this activity in the
Teacher’s Edition. If you do, be sensitive to the fact
that many students will not wish to step on scales in
front of their peers. Be sure that the students are given
the opportunity to volunteer for this activity. Also,
forewarn students that the reading of the bathroom
scale “goes crazy” when the applied force increases or
decreases by great amounts in short time intervals
because the scales inertia causes it to “overshoot”
maximum or minimum reading. Therefore, the scale
reading must be observed very soon after a dramatic
change is made in the force applied to the scale. Also
point out to students that a specific value of force is
not expected to be read on the scale during the pushoff
phase of the vertical jump; only the nature of the
change in force—e.g., greater, no change, less—needs
to be observed.