# 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.

# The hollow Einstein face

We have an illusion that consists of a hollow face of Einstein which seems to be looking at you whether you are looking at the front of it or the back. It’s very impressive. I use it to remind students (and myself) that there is a heck of a lot out there that we still don’t understand, even if we like to pretend otherwise.
The illusion can be purchased from grand-illusions.com, one of the very best sources for all types of illusions.

So when New-Scientist posted a video on how this was being used to test for schizophrenia, I thought perhaps it was time to check it out again (apparently people suffering from schizophrenia don’t notice the effect).

# Dear Wife: These are my demands

1.
1. That my clothes and laundry are kept in good order and repair.
2. That I receive my three meals regularly in my room.
3. That my bedroom and my office are always kept neat, in particular, that the desk is available to me alone.
4. You are to renounce all personal relations and refrain from criticising me either in word or deed in front of my children.
5. You are neither to expect intimacy from me nor reproach me in any way.
6. You must desist immediately from addressing me if I request it.
7. You must leave my bedroom or office immediately without protest if I so request.

So who’s the bastard?
None other than the great Albert Einstein; he made these demands of  his first wife Mileva, who actually agreed to the terms.
The marriage didn’t last much longer.

Taken from the wonderful book Quantum, by Manjit Kumar.

# Ernst Mach: the problem with Science Education

1859 marks not only the 150th birthday of the publication of Darwin’s On the Origin of Species, but also a somewhat less well-known occasion; It was the year Ernst Mach published the first of his 500 publications (his last was published five years after his death, in 1921).

Most will know of this man through his association with the speed of planes;  Mach Number is the speed at which an object is moving divided by the speed of sound.

But Mach has offered much more to the world of Science; he lived in a time when Philosophy and Science went hand and hand, and he made many contributions not just in these areas, but also in Psychology and Educational Theory. He wrote a number of text-books for school science, but was very critical of the tendency of cramming as much as possible into the syllabus.
This quote sums up so much of what is wrong with our schooling:

I know nothing more terrible than the poor creatures who have learned too much . . . What they have acquired is a spider’s web of thoughts too weak to furnish sure supports, but complicated enough to produce confusion.

Mach was also an advocate of what are known as ‘thought experiments’, these later became famous through Albert Einstein and his idea of sitting on top of a light beam.  Indeed Einstein went on to give credit to Mach for his ‘philosophical writings’.  It’s probably no coincidence that Einstein’s views on education were not that dissimilar to Mach’s:

One had to cram all this stuff into one’s mind for the examinations, whether one liked it or not. This coercion had such a deterring effect on me that, after I had passed the final examination, I found the consideration of any scientific problems distasteful to me for an entire year.

Of course this was all over one hundred years ago. Obviously it’s all changed since then.
It would appear that we have some explaining to do.