Ask The Naked Scientists

Ask the Naked Scientists SA episode

Fri, 27th Sep 2013

What Do Rockets Push Against in Space?

Another Launch (c) Mike Morley

What colour were human ancestors? What does a rocket push against in space to propel itself forward? Why does yawning make me cry? How do bats navigate? Can fuel cells run on alcohol? Why are 90% of people right handed? How genetically related would the children of two sets of identical twins be? Plus, noses grown on foreheads and how rotating antibiotic drugs can prevent bacterial resistance...

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some kind of pinky-greyish brown - sort of ape colour; nothing; because you are tired; sonar; yes; they aren't - I'll explain some other time; very; ah, that's interesting! alancalverd, Fri, 27th Sep 2013

Well that sums it up pretty nicely! And, more importantly, made me laugh.

But, you got one wrong, you also get half marks for the bats - they have reasonable vision and they use magnetism too, and you're slightly off with the genetics - the twins are equivalently related as if they were direct brothers and sisters, rather than cousins...

In fact, I posted up the twin question, because it was fun, for others to think about:

Thanks for replying anyway! chris, Sat, 28th Sep 2013

Re "they aren't" - that referred to "90% righthanders."

So here's my twopennorth on that:

The number of lefthanders has been increasing over the years, and is now around 20%. Lefties have some advantage in sports and interestingly, lefthanded CEOs earn 10 - 20% more than their dextral counterparts.

Nature doesn't usually do 10% (genetics generally works at the 50% or "very rare" levels only), and there's no reason to suspect that sinistrals are more fertile than dextrals. So we have an interesting question!

My theory is that so much of the human brain is taken up by bipedal walking and language, that half of us are genetically incapable of being ambidextrous. Our bodies are not exactly bilaterally symmetrical (they can't be!) so just as blood usually circulates in one direction through the heart (with about 0.1% of the population reversed - see above), those of us with the genetic defect tend to righthandedness whilst the other 50% have a choice. Clearly society is not going to disadvantage half of its members by being lefthanded, so the social norm, including which hand you eat with, how you tighten screws, etc, is rightist.

If you look at professions where handedness is immaterial, it seems to me that a lot of creatives and abstract thinkers are lefties. 25% of the Beatles, and the one who wrote most of the songs, was a leftie, continuing gthe tradition of Bach (certainly CPE if not JS) Beethoven, possibly Mozart (more likely fully ambi)  and Rachmaninov, just to mention a few. Very few violinists are lefthanded, but that may be due to having to share music and play in close proximity to their fellows - a leftie bow is dangerous and looks bad on stage.     

Given a free choice, a fair proportion of ambidextrals will fall in line with the rightists because that makes life easier, but as society and particularly primary school becomes more tolerant of leftism, so the number opting for that stance will increase. Hence the trend towards 25% leftism.

50 years ago a few of us looked at fellow students. You could draw a sort of subjective spectrum from pure maths on the left via science, engineering and languages to history and theology on the right, and sure enough we found that more than 25% of maths students, and less than 10% of historians, were left handed.

It would be interesting to compare the statistics of people who do similar but subtly different jobs. If my hypothesis is strong, you'd find plenty of lefthanded jazz musicians and very few leftie orchestral players. There's very little room for original thought, creativity or plain cussidness in flying, but I wonder what is the fraction of lefties  among fighter aces compared with commercial pilots?  alancalverd, Sun, 29th Sep 2013

Thanks for raising these interesting points; you may enjoy reading Chris McManus's book, Right Hand Left Hand, for which he won the Aventis book Prize about 10 years ago:

Therein he proposes a genetic model to explain the observed heritable behaviour of left handedness. He proposes 2 genes - C and D - which don't determine or pattern handedness but instead load the developmental dice towards the development of L handed brain bias.

His model fits well with the observed outcomes in the population.

Chris chris, Sun, 29th Sep 2013

With regard to the rocket in space, doesn't Newton's 3rd Law suggest that the rocket pushes back against the expanding gas in its combustion chamber which is pushing against the rocket...?  ;) dlorde, Sun, 29th Sep 2013

Yes. And that's why a rocket will accelerate in vacuum. Pmb, Sun, 29th Sep 2013

That's right, which is what we say in the programme. But the person who asked the question - alongside many others and the majority of young people who have not learned about Newtonian physics yet - didn't realise that was how a rocket works... chris, Mon, 30th Sep 2013

Just a thought:-
I always think that left handed people have some difficulty writing, because the words being written are hidden by the left hand.
This applies when writing from left to right of the page.
In many parts of the world, it is normal to write from right to left. Does this imply that, way back in history, more people were left handed?
In yet other parts of the world people write from top to bottom of the page. Does this remove any problems of handedness in writing? teragram, Mon, 30th Sep 2013

What colour were human ancestors? BROWN
What does a rocket push against in space to propel itself forward? THE ROCKET PUSHES AGAINST ITS OWN EXHAUST
Why does yawning make me cry? BECAUSE YOU'RE A CRYBABY  ;)
How do bats navigate? QUITE WELL, THANK YOU
Can fuel cells run on alcohol? NOT A HYDROGEN FUEL CELL
Why are 90% of people right handed? THEY AREN'T
How genetically related would the children of two sets of identical twins be? VERY
Noses grown on foreheads CREEPY BUT FASCINATING
How rotating antibiotic drugs can prevent bacterial resistance IF ONE DOESN'T END THE INFECTION THE NEXT ONE KILLS THE WEAKENED BACTERIA starbuck1963, Wed, 2nd Oct 2013

Thanks Starbuck1963 - you've got some of the answers right; you'll need to listen to the programme to find out which ones though!

Here's the link:

Chris chris, Sun, 6th Oct 2013

Rockets are not pushing against anything, either in or out of an atmosphere. How a rocket works is described above, i.e. reactants from rocket fuel combusion slam against the chamber wall pushing the rocket forward. The rocket itself is not pushing on anything other than the gases inside the chamber. Pmb, Tue, 8th Oct 2013

The problem is not so much the words being hidden, but the hand brushing over freshly deposited ink, smudging it. This is why you often see left-handers writing with awkwardly curved wrists so the hand is above (or sometimes below) the line of text being written. Before ball-point pens, it also meant pushing the pen nib forward rather than dragging it, so it would tend to dig in and catch on the paper, causing blots & splashes. This is probably why Leonardo da Vinci wrote his notebooks in mirror writing - not for security, but simply because, for a left-hander, it was easier, quicker, and less messy.

Probably not - there's a strong genetic influence, and prehistoric evidence suggests it hasn't changed significantly (see Skeptoid). It may just be chance, or perhaps a left-hander developed the first scripts.
Probably, although that may not be the reason for it.

Interesting questions. Many cultures have tended to exclude or revile lefties, and many enforce right-handed behaviours, so it seems unlikely that allowances would be made for them in writing techniques. dlorde, Tue, 8th Oct 2013

Ignorance of the implications of Newton's 3rd Law is not unheard of in intellectual circles - it's interesting that even the New York Times (back in the 1920's) had its doubts about action & reaction in space in response to Robert Goddard's 'rocket to the moon' suggestions. See: 'A Severe Strain on Credulity'. dlorde, Tue, 8th Oct 2013

One should never attempt to learn science from a newspaper. :) Pmb, Tue, 8th Oct 2013

How true :) dlorde, Tue, 8th Oct 2013

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