PASCO SE-8747 Kinesthetics Cart KINESTHESIA-1 - Manual (Page 12)

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Kinesthetics Cart 012-05787C
Experiment 4: Newton’s Second Law
“The Bucket Accelerator”
For a quantitative verification of Newton’s Second Law we recommend the use of a “Bucket
Accelerator”. A student of mass m
s
is riding on the Kinesthetics Cart of mass m
c
. The student
and cart experience a constant acceleration due to the constant tension force F
T
in the rope. (One
might want to return to this same setup when the Atwoods machine is being discussed.)
If there is sufficient ceiling height two pulleys will suffice. Otherwise a double pulley sys-
tem like the one shown in Fig. 4-1 can be used.
Fig. 4-1: A student and the Kinesthetics Cart of com-
bined mass m
s
+m
c
is being accelerated by a constant
tension force F
T
. The accelerating tension force is being
modified by changing the number of weights in the
bucket. The acceleration of the student and the cart is
determined with a motion detector.
➤ CAUTION!
Keep clear of the area beneath
the bucket at all times!
For a quantitative verification of Newton’s Second Law, we like to accelerate the cart and
student rider over a distance of a few meters. If a lecture hall is available with a sufficiently high
ceiling, this can be done simply with two pulleys: one mounted to the wall a few inches off the
floor, and the second one securely mounted at a suitable location on the ceiling. For classrooms
with a low ceiling or no ceiling access, one can build a simple rack and use an arrangement of
two double pulleys such that a 2 m drop of the bucket results in 8 m of travel for the cart. Al-
though pulleys are available at minimal cost at a hardware store, for quantitative measurements it
is recommended to use some heavy-duty custom-made pulleys containing high quality ball bear-
ings. A motion detector tracks the student on the cart and a computer monitor displays diagrams
of x(t), v(t), and a(t) while the student is undergoing the motion. The constant tension in the
string is monitored with a force probe. The dependence of the acceleration on the tension in the
string, i.e., the accelerating force, is obtained by varying the number of mass pieces in the bucket;
the dependence of the acceleration on the mass is obtained by using a number of different
masses. Finally, all relevant data is transferred to a spreadsheet and disseminated to the rest of the
class for evaluation.
We would like to note that the setup time for our “bucket accelerator” is comparable to the
setup time for an air track. As a precaution, it is imperative that everyone keeps clear of the area
beneath the bucket. One can place some rubber sheets and/or some foam rubber in the area be-
neath the bucket.
Although there are no real advantages to this particular way of verifying Newton’s Second
Law it is certainly more fun for the students to be a part of the experiment.