The applet above simulates pedaling a bicycle. It
operates in two modes: user mode which animates the pedal based on
forces applied by the user; and experimental mode which animates the
pedal based of experimentally determined forces applied by an actual
rider. The buttons control which mode is operating, if any. Clicking
in the selection boxes at the left allows you to see various
quantities as vectors acting on the pedal.
View the experimental animation. Examine how the total moment (torque)
varies as the forces on the pedal vary. What happens to the moment
when the pedal is on the left side of the sprocket? Keep in mind that
the moment being displayed is due to only one pedal (even if two are
being displayed).
Stop the experimental simulation. Position the crank at the top of the
cycle (12 o'clock). Click and drag on the center of the pedal to
define a 50 N force in the x- direction (be sure to have checked
"Force, x"). What is the total moment on the pedal (assume units of
N-cm)? By knowing the force and the total moment, can you determine
the length of the crank?
Now move the crank so that it points to the right (3
o'clock). Redefine the force so that it is still 50 N in the x-
direction. Now what has happened to the moment?
You can also vary the angle of the pedal with respect to the crank by
clicking on the pedal and rotating it. See how the pedal angle affects
the total moment. For example with the crank pointing toward the right
and with a 50 N force in the x-direction, how does rotating the pedal
affect the total moment.