Probing the positive
Students have difficulty relating
real world motions to a graph and vice-versa.
To probe this difficulty, construct a ball and track set-up in
class (perhaps like the diagram below), and ask the students to plot
the position and velocity of the ball versus time. Alternatively, you
can give them a plot of a particle's postion or velocity versus time,
and ask them to reproduce the motion on their desktops.
Depending on the set-up that you use, students with this
difficulty will show a wide variety of incorrect responses. The links
below point to some of the difficulties that you may see.
Related misconceptions/student difficulties that may
arise in the question:
position and velocity graphs as the path of the particle.
Velocity must be
positive, plotted above the time axis.
A positive slope for
a negative velocity means the object is speeding up.
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