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Re: Apparent weight



As an afterthought on this discussion, I'll add these comments. I believe
that the problem lies in not accepting the definition of weight for what it
is. Students feel that it is more complicated and that the definition must
change with different conditions, rather than accepting the definition as it
is. For example, sometimes bad is good.

I had a student come to me concerning a buoyancy problem. I am not teaching
the lecture, however, I do have the lab. We had just performed a lab where we
measured the density of aluminum using a torque/balance/meter-stick experiment
with an aluminum pendulum bob first balanced in air, then in water. This
student had left the lab thinking the weight of the pendulum bob had somehow
been changed when it was immersed in water. Then later, he approached me with
a buoyancy problem that he could not work in the text. I asked him what the
definition of weight was and he answered correctly. I asked him if he thought
that the object's mass changed because it was partially immersed in water. He
said no. I asked him if he thought g changed because the mass was partially
immersed in water. He said no. I saw the light go off. He suddenly
understood how simple the problem was if he did not try to change the
definition of weight. The misconception was that since it took less torque to
balance the aluminum pendulum bob when it was immersed in water, this meant
the weight changed. He was re-defining weight.

Bob Carlson