curiousity

Everything a Primary School teacher (or student) needs to know about gravity. And then some.

This post is in the context of a question posed by a primary teacher on a forum recently. Rather than reply there I thought it safer to do so where I could offer a more comprehensive answer.

We tend to associate the concept of gravity with the English scientist Isaac Newton who lived in the seventeenth century.
But he didn’t ‘invent’ gravity; objects were falling to earth long before Newton arrived on the scene, so what exactly did he do?

1.
He did what so many other kids do; he asked asked a silly question. ‘Why do things fall down?’
It does seem like a silly question, which is why nobody took it seriously before, but when you think about it it’s actually quite profound; how does the apple in an appletree ‘know’ which way to fall? How does the earth ‘know’ (if it pulls the apple down) that the apple is there in the first place ? Newton was never able to answer that question. He famously said  “Hypotheses non fingo” (Latin for “I feign [frame] no hypotheses,” or in other words, “I haven’t a clue why this works the way it does”). It’s not like there’s a string connecting the two objects, but yet the apple acts as though there were indeed an invisible string pulling it downwards.
What form does that invisible string take?

I don’t know the answer, but I do know that scientists haven’t fully worked it out yet either.
It has been suggested that all objects exchange particles called ‘gravitons’ and it is as part of this exchange process that the objects come together. The problem is that these gravitons have never been detected.

Another possibility is gravitational waves. These were postulated by Einstein in his Theory of General Relativity. There has been some indirect evidence for these but again they haven’t yet been detected directly. We know we don’t know all there is to know about gravity, and to suggest otherwise would be to do a disservice to your students. In fact the same holds for a lot of science. Gravity does seem to be a little like magnetism, yet the rules which govern gravity don’t work for magnetism and vice versa. The holy grail of physics is to show how the rules that govern the motion of very large objects like planets is connected to the rules that govern the operation of very small objects like atoms. And there’s absolutely no reason why one of your students can’t be the one to make this connection and win their very own Nobel Prize (with a bit of luck they will acknowledge  you  in their acceptance speech as the spark which ignited their passion for Science).
Matthew is a former student of mine and is currently doing a PhD with NASA on this topic. I asked him to explain it to me:

“In the Einsteinian framework, however, gravity is not a force but a curve in space-time. So any object with mass induces a curve in the spacetime around it. Any other object no longer travels along a flat spacetime, but along a curved path. That’s essentially what’s happening to the apple. Instead of hovering at the end of the branch as it would in a flat spacetime, the ‘forward direction’ of spacetime is curved due to the Earth, so the apple just follows that curve, which in three spatial dimensions is just a straight line down.”

Watch the following clip for a wonderful demonstration of a curving space-time –  imagine doing this with your kids in class: you can tell them you are studying Einstein and doing Rocket Science.

But while Newton couldn’t say why gravity worked, he was able to quantify the force of gravity, i.e. he was able to devise a formula which now enables us to say how big the force of attraction will be between any two objects. It depends on how big the objects are (or more specifically their masses) and the distance between them.

It turns out that any two objects will exert a gravitational pull on each other. Now this is mad. It means that there is a force of attraction between you and your biro, and if it was just the two of you floating in space with no other objects or planets in existence, that force of attraction would result in the biro moving towards you and you moving towards the biro. Similarly there is a force of attraction beween each student and the student next to them (cue lots of giggles) and the bigger the size (or mass) of either student, the bigger will be the force.

2.
Newton also established that the force that kept the planets in orbit around the sun was the same force as that which pulled the apple to earth. This idea was a big, big deal at the time. It meant that the planets followed the same laws of physics as objects on earth. Prior to this ‘the heavens’ were thought to be the realm of the gods or God and therefore not subject to our analysis but after Newton they were seen as fair game for anybody to study. I don’t think there’s any way we can really appreciate how big a deal this was. And while Newton wasn’t the very first to realise this, he was the first to demonstrate it mathematically.

The following is a nice video which outlines the significance of Newton and Einstein to our understanding of gravity. You only need the first ten minutes.

The bottom line for me is that you have an incredible audience who will lap this stuff up. Please, please don’t play down the mystery or the wonder. That, unfortunately, is what happens at second level and I have been trying to get teachers to fight it my entire professional career, with very limited success (it doesn’t seem to bother many other teachers, but I have it bad).

Don’t allow your lack of technical knowledge to put you off engaging with the material. Remember when it comes to Science nobody, and I mean nobody, has all the answers. If we’re looking to turn some of these kids into scientists then what they need more than anything else is curiosity and a good old-fashioned sense of wonder. If you can help develop that then everything else will follow.

My contribution to Science Week – I thought I might teach some physics

At 40 mins long it’s not going to go viral anytime soon. It’s the middle 40 minutes of a double class but in it we managed to learn about some of the following:

The structure of the atom.

We, and everything around us, are mostly empty space.

We discovered that the appearance of  ‘solidness’ is an illusion – which lead to a  discussion about how light works.
We learned that there is a cultural aspect to what we see (and you definitely won’t find that in physics textbooks) and that Newton himself was subject to this and it resulted in him making a boo-boo that still goes uncorrected right up to today.

We discovered that electrons are constantly cascading down along everything we see in a seemingly never-ending avalanche, powered by energy from incoming light (so when this power source disappears, the electrons no longer have energy to jump up or fall back down, otherwise known as darkness).

We learned why things feel solid – all to do with the force of repulsion between electrons at the surface.

We developed a deeper understanding of Newton’s Third Law.

We discussed the fallacy of language – know the word for something (like gravity) and understanding what gravity actually is are two very different things, and shouldn’t be confused with each other.

We discovered that physics teachers don’t have all the answers, and should never pretend otherwise.

We were reminded that because almost none of the above is in the syllabus, the syllabus is a disgrace. It’s no wonder students don’t see the point of it.
There were 22 students in that class and the discussion could have gone on and on – I had to kick them out the door.  One can only imagine the conversations they must have had over the dinner table that evening.

If only all those who make such a fuss over Science Week could put a fraction of that effort into making the school syllabus a source of wonder and curiosity instead of what it is – a series of dull as dishwater facts which are to be merely learned off by heart.