Surface tension

I don't know why I have never dealt with surface tension here: it is in at least two of my books. Here is how I have dealt with it in What On Earth?

Water has a property called surface tension. The why of surface tension is hard top explain, so the simple explanation is that surface tension is caused by polar water molecules all pulling each other together. Don’t worry too much about the why: the main thing is that the effects are amazing.

For example, water forms drops that stick together. Without surface tension, there would be no raindrops. Next, lots of insects and spiders can walk across a water surface. In fact, you can even make a paper clip sit on a water surface, but it isn’t floating, not as we usually mean ‘float’!

Many of the strange things that water does depend the effects of surface tension. This is a complicated idea, but you can see surface tension in the way wet hair clings together or the bristles of a paint brush stick to each other, but better, you can demonstrate it this way. 

You need two paper clips and a glass of water. Follow the pictures that you see here: bend one paper clip into an L shape. Use this clip to gently lay another paperclip on the top of the water. The surface of the water bends under the weight of the paperclip like stretched rubber, but doesn’t let it through.

You need to pick up one paper clip with the other. The next part needs a steady hand, or it won't work. You are going to lower the unbent paper clip onto the water surface like this:

The next step is to push the supporting paper clip down. With any sort of luck, the supported paper clip will 'float'. Let me say again, this is not really floating.

If the trick doesn’t work, pull the paperclip out, dry it carefully and rub a tiny bit of grease on the paperclip before trying again.

If you look closely at the reflections coming off the water in the photo on the right, you can see how the water surface is bent. To push the water surface out of shape you must use force.

If the paperclip can’t exert enough force, it can’t stretch the surface enough to let the paperclip slip through. All the same, one drop of detergent in the water, and all the magic goes! (No, I won’t explain why!)

The case of the sensitive seismometer

This is a short excerpt from What On Earth?

This is a guide to how earth science works, because many parts of earth science leave lay people asking questions like How can we know what a once in a thousand years flood looks like.

Actually, I have already covered that one, and I used part of that blog entry in What on Earth?

There is a seismometer in Spain which has often detected odd things. It is 500 metres away from the Camp Nou stadium in Barcelona, in the basement of the Institute of Earth Sciences Jaume Almera of the CSIC (in Spain, it is called ICTJA-CSIC).

In May 2016, Bruce Springsteen and The E Street Band held a concert at Camp Nou. When 65,000 spectators danced to their songs, researcher Jordi Diaz found that the seismometer recorded the vibrations caused as the crowd jumped together. Here is the seismic record of the Springsteen concert:

The graph that appears below this shows the seismometer readings during Springsteen’s performance. Can you work out when he went from one song to the next?

At other times, the same seismometer has detected underground trains, traffic patterns (including the rush hour in Barcelona) and nearby fireworks, but the best of all was when the instrument detected Catalan enthusiasm at a football game in May 2015. The football club FC Barcelona, whose home ground is the Camp Nou stadium scored three goals in the last 15 minutes of a Champions League semi-finals game against Bayern Munich, and the fans’ celebrations showed up clearly.

This story was republished with the assistance and permission of Jordi Diaz and ICTJA-CSIC.

It ain't half wet, Mum

I have been rather engaged in writing for publication, so here to prove that, like Granny Weatherwax, I aten't dead yet, here's a sampler about a little-known event that I came across while in NZ.

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Into every life cycle, a little catastrophe must fall, and in the Carnian stage of the late Triassic, the geological record shows what seems like a long monsoon. That, at least is what the evidence suggests, but ‘long’ is a weak descriptor for a wet spell that went on for a million years, or maybe two. At the end of the downpour that was the Carnian pluvial episode (CPE), the lepidosaurs (the ancestors of the modern-day snakes and lizards) were present, and so were the mammaliaforms (the ancestors of the mammals). The heavy rains had triggered some major changes.

Quite a few invertebrates went missing at this time from among the ammonoids, bryozoa and crinoids, so what caused this changeover? At that time, there was just one continent, Pangaea, and the sea was probably hotter than it is now, so there would have been enough water in the atmosphere to feed continual torrential rain. To make things worse, there were huge volcanic outpourings at this time, generating the flood basalts of western North America.

Basalt flows, Snake River, Washington state, USA.

That sort of volcanic activity makes things warmer, and it also injects lots of water vapour into the atmosphere, and also lots of CO₂. This would have fed global warming, again raising atmospheric water levels, and down came the rain, in the Carnian Stage, a subdivision of the lowermost Upper Triassic period. On 10 November 1987 Alastair Ruffell and Michael Simms linked a stripe of grey in the red stone of Somerset’s Lipe Hill to Simms’s research on crinoid extinction in the mid-Carnian.

This period was about 234 to 232 million years ago, and aside from wiping out some branches of life and opening the way to others, the CPE left a number of traces in the rocks. These include clay deposits in sedimentary basins, pollen traces that reflect vegetation that thrives in humid conditions, lots of amber, and many changes in the isotope balances.

The oxygen isotope ratios (¹⁸O:¹⁶O) alter, suggesting global warming of 3 to 4°C during the CPE (though this could also point to a change in seawater salinity). The carbon-13 levels rose and fell in parallel with higher levels of sedimentation (which points to higher rainfall).

In other words, the world may survive massive changes in the climate, but can humans manage to cling on? That is probably a key question for the generations after mine, and also my generation, if we have a descendant-based interest in the future.