Don't Ever Mention "Centrifugal Force" to Physicists

[neilparker62]

I've just come across the following line while studying (Young & Freedman) and found it amusing.

It sounds like a dirty family secret we discuss once and then should never mention again

I think he said "Oh centrifugal"

 

[sophiecentaur]

My point of disagreement is that Ohm's law necessitates a range in which R is constant. It works perfectly well where there is no linear range of R.

Why do you put it that way round? Ohm stated the experimental condition that it's temperature that remains constant and he was talking about metals - not diodes etc.. The Physics of metals describes why Ohm got it right (luck and a lot of careful measurements). Semiconductor Physics shows that his law doesn't apply over even very small variations of current and temperature.

The ratio R is valid (of course) and we can use it in our calculations but why is it referred to as "Ohm's Law"? We are happy to use other 'laws' and to include the "all other things being equal" clause - for instance in the subsets of the Gas Law, Boyle's Law and Charles' Law, in which one of the three variables is stated (assumed) to be constant.
But for some reason (familiarity and bad teaching?) we carry on exposing newcomers to two versions of Ohm's Law. And so it continues.

In the case of Centrifugal Force, it's clear why our education starts with "there's no such thing". It's to knock on the head the mistaken idea that the ball 'flies outwards' when the string is cut. That's a misapprehension along the lines of 'things always slow down' and it's what we all experience (or think we experience). It's all a matter of the order in which things need to be taught appropriately on the way to improved understanding. The concept of a reactive force demands a formal level of thought which we lack early on (except for those PF members who seem to remember having grasped all of Physics first time round at school).

I think that Science shares the same problem that politician have, the fear of the U turn and dealing with the complaint that 'you taught us wrong', when we teach better models. Kids do their early learning at a concrete level and they appreciate concrete thoughts. We are not letting them down by not plunging into String Theory when they first ask us about simple Mechanics.