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There was a recent discussion on Twitter about the use of the term "preconception" instead of "misconception" to talk about the difficulties faced by students. The debate goes back several years, but it still deserves to be examined. So: how should teachers handle the problems faced by students in introductory courses and how to call them?
Let's start with a particularly common student idea. Suppose I receive a low-friction trolley and push it so that it moves along a track like this.
An occasional observation seems to indicate that this cart is moving at a constant speed, which is essentially true. But why? Why does the cart move at a constant speed after being pushed? Here I am going to make it a multiple choice question for you.
A. The carriage moves at a constant speed because there is a constant force to push.
B. The carriage moves at a constant speed as the initial force of the thrust is transferred to the carriage.
C. The carriage moves because it does not exert any force.
RE. The carriage moves for another reason (and describes the reason).
I am pretty sure that many students would agree with any of these options. In fact, the most common answer will probably be a combination of A and B, namely that the carriage moves because a constant force pushes it. If you ask them to name this force, they could call it "force of movement" or "force of thrust". Of course, the answer corroborated by the physics models is that the carriage moves at a constant speed because it has no net force.
Rhett Allain, an associate professor of physics at Southeastern Louisiana University, writes about physics for WIRED.
Now, do students have a misconception about this situation? Are they just wrong? Nope. Here's the important thing to remember: students have ideas based on something that makes sense. Humans do not just do crazy things. (Not normally.) Instead, we build ideas based on previous experience and these ideas must have some kind of logic.
How about a similar case? Here is a block without wheels. How can we get this to move at a constant speed? Yes, you have to shoot it. Here is what it would look like.
It's something that almost everyone has known. It may be pushing a book on a table or pulling a chair off the floor. It is clear that if you want to move it at a constant speed, you must push with constant force. This idea of "constant force means constant movement" should also apply to the low friction carriage. Of course, there is a very significant difference between the two objects that move at a constant speed. The second block was subjected to a frictional force, while the rolling carriage showed virtually no friction. You can not really see the friction and it is sometimes difficult to see that it is a force, but it is there. Thus, in both cases, the object moves at a constant speed with zero net force.
Therefore, the "misconception" here is not completely wrong. By calling this a misconception, we tell the students that they are wrong. But their ideas are not bad, they develop. That's where the term "preconception" comes from.
Who cares about this anyway? It is important. If you want to structure a course to help students develop and develop ideas, you need to know where they start. The instructor really needs to know what these initial ideas are in order to introduce students to new situations that help them to change these ideas.
You can understand what your students think of this or that concept in two ways. The most obvious way is to ask them. Really, it's a good idea to do a little checking once in a while. Give students an activity or question on the subject. For the example of the above forces, just ask what forces are on the carriage after pushing.
The second method to determine the preconceptions of students is the experience. For the forces on a cart question above, I did not actually ask any students. However, I've been teaching these ideas for quite some time. I have a good idea of what they will say (although students may still find a way to surprise me from time to time). If you do not have experience with students, many textbooks offer teachers materials describing some of these common ideas. There is also the book Introductory physics teaching by Arnold Arons (Wiley, 1996). This book addresses a wide range of introductory physics topics. It's a classic.
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