a gap in my scientific knowledge!

[baratron]

I've just had a very confusing half hour.

I was supposed to be having a voice class this afternoon. According to the timetable, these are classes to help us learn voice projection techniques. Well, we had precisely one lesson with a speech therapist, and she spent the whole time telling us about diseases of the throat, showing unpleasant biological videos of such, with a few minutes about how to avoid them (apparently drink herbal tea and avoid eating sandwiches. Lots of what not to do, and not enough about what to do. Hmmm.

In today's session, we were supposed to have been giving a prepared 5 minute presentation about a topic outside our own science specialism (without using a whiteboard, OHP or paper) and also tell an interesting or amusing scientific anecdote. I fondly assumed that this would be run by a member of staff, who would check our clarity and projection to different parts of the room, and make constructive comments for improvement. No such luck. Instead, we were supposed to present the information we'd found to a group of 3 or 4 other students.

How talking to 3 other people is supposed to help us project to an entire classroom I didn't find out, as no one else turned up. Well, they may have done - but they'd gone by the time I got there. As my morning class finished at 12.30 and my afternoon class wasn't until 3.30pm, I thought I'd go home, have a shower, and pick up the work I left behind this morning when I was too brain-dead to remember what I needed. Of course, it then took me forever to wash my hair, and then the trains were all screwed up, so I didn't get to college until 3.50pm. I went to the room where the class was supposed to be, to find no one there. After wandering around a bit looking in all the likely rooms, I found some people in the common room who'd been timetabled for the earlier class (2pm), and they said hardly anyone had bothered to turn up, and they'd just chatted about random stuff for 20 minutes before giving up. How ... helpful. (You mean I rushed across London for nothing?)

On the basis I thought there was actually going to be a class today, I spent last night trying to prepare a topic. After looking through the list of topics and panicking wildly as they all seemed to be either chemistry or stuff I'd never done (the range of joints in the human body? the structure of proteins or DNA? They weren't in GCSE biology when I was a kid!) I found "What is the difference between force and pressure?", which seemed to be something I should know about.

But I found that although I could find simple definitions in my books for pressure (a force acting over an area), I couldn't find a good definition for force! I looked in four textbooks and did a google search, and the best I could come up with were "examples of forces are pushes, pulls and twists" or "a force is the physical influence which when exerted over a distance causes work to be done" / "a force is the physical influence which causes a body of uniform mass to accelerate". The first definition isn't really a definition at all - it's giving examples of forces without telling me what a force is, and the second two are just statements of well-known equations in words. Not very helpful for my understanding or for my ability to explain this to kids.

Anyway, the people in the common room were physicists, so I tried to ask them for a definition of force. And they kept telling me either that forces are "electrostatic, gravitational, or strong or weak nuclear forces" (i.e. giving examples of forces as a definition) or that a force is "pressure divided by area" (restating an equation in words). I said "I understand what pressure is - it's a force acting over an area, so the same force over a small area gives a big pressure. Now tell me what a force is!". And they just couldn't. They said I'd have to know particle physics to understand it, and I said "How can something so fundamental not have at least one simple definition? - even if that definition has to later be extended?".

We went round and round in circles like that for some time. They kept either giving me examples of forces or restating equations. I said "It's like telling me that some types of furniture are beds, chairs and desks. Which I understand - now tell me what 'furniture' is!". Or "I want to know what a chair is, and you've told me that a chair is a type of furniture, whereas what I actually want to know is that it's something you sit on". I don't know. Are those analogies really that bad? (I thought they were okay for spur-of-the-moment things!). Eventually, after around 25 minutes of arguing, we managed to hash out that a force is "an interaction between matter". I asked if that was always true, and they thought it was (although some of the interactions are on the subatomic level).

Ye gods! The word "force" is all the way through school level science! It's introduced in Key Stage 1 (which they do at ages 5-7!). And yet it's taken a chemist nearly half an hour to prod an acceptable definition out of two physicists! I'd go "Gah, physicists", but I know the problem's not with them personally. How can we teach something that's fundamental and at the heart of the subject without a useful working definition, and expect the kids to actually understand it? "A force is a push or a pull" is fine for Key Stage 1, but by GCSE I'd expect more scientific language - but the language that's used is just restating the formula. If you don't understand where the formula came from, what use is restating it in words?

Comments

[barty.livejournal.com]

In GCSE physics I was taught Newton's Second Law Of Motion - the law that quantitatively defines what force and mass are: "Force equals mass times acceleration".

In A-level physics I learned about vectors and that mass isn't always a constant (eg. when you are filling up a moving train with sand) so it is better to say "Force is the rate of change of momentum".

In first year undergraduate physics I had to write an essay about how we didn't really know what mass is. It seems force and mass are only real in relation to each other.
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[easterbunny.livejournal.com]

Circular definitions are frustrating, but what about this definition: "force is anything that can cause change in a massive object's speed". This is from Astronomy Connection: Gravity and Black Holes (http://www.adlerplanetarium.org/education/ac/gravity/curriculum/gq2.htm). Not very technical, but easier to visualize than "A vector quantity that tends to produce an acceleration of a body in the direction of its application" (from dictionary.com).

[lovingboth]

I'm surprised vectors took so long - this was O-Level maths as well as physics for me.

But yes... force is what changes momentum.

[jinian.livejournal.com]

I would say "force is that which overcomes inertia," myself, and elaborate as needed. The part about two objects being present is important, too. I think it's actually less likely to find someone who can explain nice simple Newtonian physics when you go to more physics-educated people; it gets all muddled. I, who have taken the 101 class and no more, am clearly the ideal teacher. :)

Sounds totally frustrating, sorry you went through that.

[meeping.livejournal.com]

"A force is a push or a pull" is fine for Key Stage 1,

I kind of like this definition and I think it is actually probably the most useful so far, and probably the best of way to actually get a grasp of what a force _is_, rather than its effects.

I am thinking that are that if you maybe expand push and pull to attraction and repulsion, we could define a force as either an attractive or repulsive interaction between two bodies. I am not sure if that defines it completely accurately e.g., you might need to say two or more bodies, and there could be forces which are neither attractive nor repulsive ( but I couldn't think of any!)

[lizw.livejournal.com]

the language that's used is just restating the formula. If you don't understand where the formula came from, what use is restating it in words?

This is where you lose me, because to me the formula is the definition.

[eub.livejournal.com]

Eventually, after around 25 minutes of arguing, we managed to hash out that a force is "an interaction between matter". I asked if that was always true, and they thought it was (although some of the interactions are on the subatomic level).

On the other hand, not all interactions of matter are force. Which ones are? The ones that push. Hmm.

I wonder, is one of the challenges in teaching about force to distinguish between force and pre-Newtonian impetus? Impetus seems to lie deeper in our wiring; it just doesn't make for a useful physics.

(Hi, you're a friendfriend.)

[baratron.livejournal.com]

My problem with using a formula as the definition is that in this particular example, no single formula adequately defines the quantity.

Take Newton's Second Law, usually abbreviated to the equation F=ma (a force is something that causes a mass to accelerate). That's ok as far as it goes, but I can instantly think of one example where no acceleration takes place: the tug of war. Say you and I are both pulling on a rope, and we're pulling the same amount, so we're not moving. No apparent acceleration is taking place because we're not moving - and yet clearly several forces are occurring, because we can feel them in our arms!

Well. People who have studied maths and physics to a higher level know that force is a vector quantity. And thus a force acting on an object that is perfectly balanced by a force of the same size in the opposite direction has an overall (or resultant) force of zero. As the forces balance, there is effectively no force, and so the object does not accelerate. But saying "there is no force" because the forces balance is... frankly, far too woolly for me. It's bad enough having to try to explain physics that contradicts real-world experience (the fact that according to Newton's First Law, a body that has been subjected to a force will travel forever without any more force needing to be applied. Because on the earth there is always friction or air resistance or both, this does not happen - you have to maintain a constant driving force to overcome the opposing forces of friction. Thus, this principle is very difficult for a child to understand.) - but saying "these forces balance so effectively there aren't any" to kids too young to have any idea about vectors vs scalars (they only do them at higher level GCSE) just does my head in! I dread to think what it would do to the kids!

[lizw.livejournal.com]

I think the key thing to teach a child is that science is a cultural construct, made by humans to enable us to model real-world processes. A good-enough model is one whose outcome is a good-enough prediction about the outcome of the real-world process, for whatever purpose we want the prediction for. The individual components of the model, such as the concepts that are used and their definitions, don't have to correspond to any real-world "out there" thing that you can point to. A lot of my confusion in science classes came from teachers not getting that basic point across.