PASCO SE-8747 Kinesthetics Cart KINESTHESIA-1 - Manual (Page 8)

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Kinesthetics Cart 012-05787C
Experiment 1: Newton’s First
Most often we find Newton’s First Law paraphrased in a form like this: “A body will remain in its
state of motion unless acted upon by an external force.” We can paraphrase it even a little more to
accentuate the essence of the First Law for our students and word it something like this: “A body
moving at constant velocity v
c
will keep moving at this constant velocity v
c
, no matter what hap-
pens to the world around this body, unless acted upon by an external force.” This of course contra-
dicts our everyday experience: our car will not keep moving at a constant 55 mph unless we keep
applying a steady force. Here, Kinesthesia-1 affords a unique opportunity for students to experi-
ence in the classroom that Newton is correct indeed.
At the center of the classroom (or any other convenient location of the lecture hall) a short
section (approx. 4”) of a two-by-four is attached to the floor. A student rider initially has both carts
coupled together and is accelerated to an initial velocity v
c
by his or her partner. As soon as the
student rider has attained the constant velocity v
c
, (s)he separates the two carts by pulling the cou-
pler straight up. Now, the student rider and the upper cart ride quasi friction-free, piggy-back-style
on top of the lower cart, approaching the two-by-four block in the center of the classroom. A few
seconds later, the worst case scenario happens. The two-by-four block abruptly stops the lower
cart, i.e., the world underneath our rider comes to a complete stop. But what will happen to the
upper cart and the rider? If Newton is right, the upper cart and the rider will, contrary to our every-
day experience, continue to move at a constant velocity v
c
, since there is no force acting on them.
Indeed, this is what our rider experiences. As the top cart and the rider keep moving beyond the
limit of the lower cart, the “landing gear” (roller blade wheels on the upper cart) ensures a fairly
smooth landing. This kinesthetic experience not only verifies Newton’s First Law but with the
small jolt of the touchdown the First Law is ingrained in the students’ memory and will be remem-
bered for a long time past this experience.
Figure 1.1: A student rider is given a constant veloc-
ity v
c
by her partner. The upper and lower cart are
coupled together.
Figure 1.2: The student rider removes the coupler
as she approaches the 4”x4”x2” block mounted to
the floor.