PASCO SE-8747 Kinesthetics Cart KINESTHESIA-1 - Manual (Page 10)

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Kinesthetics Cart 012-05787C
Experiment 2: A Special Case of Newton’s First Law
Figure 2-1: A student rider sits on the decoupled
Kinesthetics Cart awaiting for some drastic event to
happen. Then the “world” underneath begins to
move suddenly when a second student pulls on the
rope which is attached to the lower cart.
Kinesthesia-1 is also perfectly suited to illustrate the v
o
= 0 m/s case of Newton’s First Law.
Here again, we paraphrase Newton’s First Law to get the decisive point across: “A body at rest
will remain at rest unless there is an external force acting on it!” Or even more pronounced: “A
body at rest will remain at rest no matter what happens to the world around it, as long as there is
no external force acting on it.” To illustrate this special case of Newton’s First Law, a student is
sitting in anticipation on the decoupled Kinesthesia-1 cart as illustrated in Fig. 2-1. The instruc-
tor, holding the rope that is tied to the lower cart, solicits a prediction from the student and the
rest of the class. If Newton is right, the student rider should not move. As the instructor acceler-
ates the lower cart out from underneath the student the upper cart lands gently on the landing
gear. With this gentle impact this special case of Newton’s First Law is imprinted into the stu-
dents’ brain. We would like to note that this experiment works better than the traditional demon-
stration of the table cloth trick since the inertia of a student is in general larger than the inertia of
a dinner plate.
Figure 2-2: The student rider and the upper cart
having no force acting upon them remain at rest as
the lower cart is pulled out from underneath. The
roller blade wheels of the upper cart (the “landing
gear”) are designed such that the student rider and
upper cart drop only a very small distance.