Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] F causes a



To sum up, neither this example nor the many examples that
preceded it provide any appreciable support to the notion that
"F causes ma (and not vice versa)".

As I alluded to in another response, I agree. My block in the face example was intended as a counterexample to Jim's notion that there is a direct cause-effect notion that can only go one way (force -> acceleration).

I do not teach for a living (you may thank me later). But if I did, I think I would try to structure my teaching around several of the concepts discussed here. Knowing what I was faced with from an educational standpoint, I would want to try to teach physics in an intellectually honest way, but also not let kids graduate without making at least SOME connections. This means get into the subject matter, be pedantic to a degree, but not so much that they can't learn something. Most of them will never think about it again anyway; might as well make sure they might remember something worthwhile. Hence my 2 cents:

1. F = ma. It's an equation! With a tremendous history no less. There is no particular cause/effect relationship to be determined from it. I think that F(t) = ma(t) sums that up about as well as can be.

2. Recognize that people are born and raised to view things as cause/effect. This moment is supposedly what makes you a teacher. Teach that physics has some very interesting things to say, and not say, about it. You might be surprised at the degree to which the "uneducated" can conjure a "Hey I've been looking at this all wrong! Cool!"

3. In particular, it is very comfortable to the student to state that forces cause accelerations. No matter how you start, they will restate it back in those terms. Use it as a teaching moment, reiterating that F=ma really makes no statement about cause/effect per se, and that to some it will make more sense to write a = F/m, but that there is no particular need for this. Do what you need to make it click. Wouldn't you be thrilled as teachers to at least have more of the students not fail the pop quiz over and over?

4. When you have an opportunity, explain the difficulties and nuances of cause/effect relationships, or even what cause/effect means on a deeper level. It seems to me that this part has to be tailored to the target audience, just as a practical matter. The discussion would evolve (and end) differently, depending if they are HS, college, or real physics grad students. If they are really interested, point them to this thread in the archive - they will learn some physics, and even more about some physicists.


Stefan Jeglinski