PASCO SE-8747 Kinesthetics Cart KINESTHESIA-1 - Manual (Page 22)

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Kinesthetics Cart 012-05787C
Experiment 13: Newton’s Third Law Misconception;
“Only the moving object exerts a force”
Physics education researchers have found that some beginning physics students hold on to the belief that
“only the moving object exerts the force.” The object at rest is “being pushed or pulled.”
This conception is readily corrected using a slight modification of Experiment 12. Both cart bumpers
are again equipped with soda cans. However, this time one rider and his/her cart remain at rest. As the
second cart crashes into the stationary cart both sets of soda cans again get equally crushed thus verifying
Newton’s Third Law.
Experiment 14: Newton’s Third Law Misconception;
“The more massive object exerts a larger force”
Here is another example of how Kinesthesia-1 can be used to correct a misconception. Consider
a collision between a heavy truck and a subcompact passenger car. Asked about which of the
two exerts the larger force, students respond confidently, that the truck exerts a much larger force
on the subcompact. This misconception clearly stems from “truck-passenger car collisions” that
students have either witnessed in person or seen on TV. However, the fact that the subcompact
got totaled while the truck escaped with a few dents, is not due to unequal forces, but a conse-
quence of unequal material strength.
We can readily counteract this misconception with Kinesthesia-1 and the collision attach-
ment. We place one light-weight rider on one cart and fit two heavyweight riders on the other
cart thereby approximately tripling the mass of the first cart and rider. (Be sure not to exceed the
maximum load capacity of the Kinesthetics Cart.) Independent of the velocities v
1
and v
2
of the
two carts (m
1
= m, and m
2
≈
3m), the soda cans will be crushed equally, thus again verifying
Newton’s Third Law.