Physics 115: Inquiry Into Physics
Section 1 David Hammer
First assignment, due Tuesday Sept 6.
There are two questions in this assignment. Read them carefully; think about
them; think about how you're thinking about them. What assumptions might
you be making? What assumptions might someone else make? What
knowledge and experience do you have that might be related?
Please do talk with others in the class– it really helps to get other perspectives –
but, please, write your own essays. And, please, don’t go ask your friend the
physicist or the engineer, or look for answers on Google. That sort of thing
won’t help you in this course! It could even hurt.
Along the same lines, don't worry about being "right" just yet! You're
shopping around and collecting ideas, mostly from your own mind, and if you
worry too much about being "right" too soon you're liable not to find as many
good ones.
Please type or print on a word processor (be sure the ink is dark enough to be
read), and make three copies (one will be for me and the other two will be for
fellow students in class).
At some point we might work it out to exchange your essays by e-mail, but
most people have a hard time drawing good pictures on the computer—either
they don’t know how to do it or it takes them a long time. (Some graphic artists
get very good at it.) And for almost all the questions in this course, it’s going to
be hard to express your ideas clearly without drawing pictures. So for this first
time anyway, please bring in printed copies.
Two pennies
Suppose you have two wheels of the same size, and you roll one of them around
the other. That is, you hold one wheel fixed and have the other wheel roll
around it. You could try it with a couple of pennies, as shown in the figure.
Hold one penny still, and place the second penny on top of the first so that it's
touching. Then roll the second penny around the first, keeping the first from
moving. (Be sure to roll the second penny around the first, without any sliding.
Quarters might be easier to use, because they have ridges that give a bit of
"traction.")
The question is this: if you roll the second penny
exactly once around the first, so that it ends up
back where it started, how many times will you
see Lincoln's picture on the second penny upsidedown?
Explain at least two different ways of thinking
that could lead you or someone to different
answers. In particular, explain:
A) your first impression for what should be the answer, and try to identify
what in your knowledge and experience is giving you that impression;
and
B) at least one other answer you or someone else might give, and try to
identify what knowledge and experience would lead to that answer.
(This is a question format we’re going to use throughout the course, with the
addition of a part C to ask what doesn’t work about the reasoning in part B. For
this first assignment, I’m only asking you to answer parts A and B, but feel free
to add part C if you are so inclined!)
Lighting a bulb
Suppose you had a battery ,
some pieces of wire
a little bulb,
and
(they bend!).
Show how you might connect or touch them together so that the bulb lights.
Again, explain at least two different ways of thinking that could lead you to
different answers:
A) your first impression, and what in your knowledge and experience gives
you that impression;
and
B) at least one other reasonable possibility, and what knowledge and
experience would have someone think that way.