Re: [Phys-l] More Stupidity in state exams

["Dr. Keith S. Taber" <kst24@cam.ac.uk>]

At 14:44 -0500 9/8/11, John Clement wrote:
> Which of these happens after a baseball is hit at a constant speed 
> with a baseball bat?

I don't understand what is meant by "is hit at a constant speed". 
Must be an American thing - it would not be possible in cricket.

Does it mean the ball was moving at a constant speed before impact?
Or that the bat was moving at a constant speed before impact?

Neither of them are going to be moving at a constant speed during the 
short period of the impact

I suppose theoretically the bat could be. IF the batsman was applying 
just the right force to the bat to compensate for the change in 
momentum of the ball - but in practice no human batsman could do this 
on the time-scale of the impact.

(I'm not sure the 'after' is actually a sign of a misconception, more 
likely bad phrasing: i.e. it is meant to be asking which of these 
would be the case after [the impossible interaction] compared with 
before - but it could certainly be interpreted that way.)

Some errors in National Exams are inevitable, but here there is 
usually a rumpus when they are spotted (in the national press for 
example), so exam boards - which are in competition with each other - 
have a strong motivation not to make too many.


> As to biology misconceptions virtually 100% of my calculus based 
> physics students agreed that "bonds contain energy".

The terminology 'energy-rich phosphate bonds'is not helpful in this 
regard, but perhaps 'easily-disrupted-by-energy phosphate bonds' does 
not have quite the same ring? Of course, energy does tend to be given 
out when these bonds break (in the context of the whole reaction 
going on), and I think some biologists feel it is therefore being 
pedantic to point out that like any bond energy is required to break 
them. I've rather come to the view that whilst this is an alternative 
conception acquired by students, for some of the biologists this is 
more a different formalism reflecting their own disciplinary concerns 
and priorities rather than an actual misunderstanding of the science 
(just as some chemistry teachers seem to think that explaining 
patterns in successive atomic ionisation energies in terms of the 
sharing out of nuclear force is fine as it's a useful heuristic that 
generally works).

Keith





--
Dr. Keith S. Taber

http://www.educ.cam.ac.uk/staff/taber.html
http://people.pwf.cam.ac.uk/kst24/

Author: Progressing Science Education - Constructing the Scientific 
Research Programme into the Contingent Nature of Learning Science 
(Springer: 2009)

University Senior Lecturer in Science Education

Science Education Centre
University of Cambridge Faculty of Education
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