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Re: [Phys-l] irresistible force v. immovable object



On 02/23/2011 11:25 AM, Mike Viotti wrote:
Here's an equally valid question:

What happens if a blorp comes into thermal contact with a slurg and all the
marfs are turned into storgs?

Who cares? There's no such thing as either an unstoppable object or an
unmovable object. Everything can be stopped and everything can be moved.
As John pointed out, this is not a physics question, it's a philosophy one.
Just so long as students understand the domain of the problem, you can tell
them whatever you want. Hell, go ahead and agree that the world will end.
But no matter what you tell them, it isn't physics.

I wouldn't have said that. The example is not equally valid.
There *are* physics problems that closely correspond to the
original question.

As I see it, this is a case of the student's reach /slightly/
exceeding his grasp.

IMHO it is a glorious achievement that humans can even imagine
the idea of infinity. We can sometimes make sense of things
like infinity over infinity or zero over zero ... and we can
systematically separate the cases that make sense from the ones
that don't.

On the other side of the same coin, this is a tricky business.
The fact that students have a hard time with it does not come
as a surprise, and does not bother me in the slightest.

Slurgs are not physics, but lim(Δy/Δx) is physics. When the
student starts asking about such things, it's a teachable
moment ... or at least a motivational moment. Tell 'em the
precalculus course and especially the calculus course will
allow them to make sense of such questions. Newton invented
calculus so he could do physics, specifically so he could
deal with physics problems of this ilk.

Another well-regarded resource suitable for high-school (and
younger) readers is:
George Gamow
_One, Two, Three ... Infinity_