Miscellaneous

Hi! Here you'll find a fun science snippet and a physics tip, followed by a brief note about my name.

(Click here for previous snippets & tips)

A science snippet: The Earth is rotating a bit faster these days... reason(s) yet to be determined

The Earth rotates about its axis, with a period relative to the incoming Sun's rays of almost exactly 24 hours (86,400 seconds). Actually, being not totally rigid (it's made from solids, liquids, and gases which each deform due to internal stresses, weather effects, and the motion of the Moon) it rotates a little erratically. This plot from 2000 to the present day shows small daily and seasonal differences in the length of a day from exactly 86,400 seconds by about a millisecond or so. Besides these variations, for millennia the Earth has on average slowed down, with the average length of a day increasing by about 1.8 ms every century for the past few thousand years. We currently adjust for days having an average length greater than 86,400 seconds by occasionally adding a "leap second" to our clocks to keep them synchronized with dawn and dusk.

As the plot shows, however, between 2000-2005, and also since 2016, days have been on average (the black line) getting shorter, which means the Earth has been speeding up. Indeed, since 2020 the average length of a day is now less than 86,400 seconds, so we may soon need to subtract, rather than add, a leap second or two. There are several possible reasons for this change, from glacial effects to wobbles of the Earth's axis. We'll have to wait for the physics folk who study the complex place that we call home to arrive at a testable - and tested - hypothesis to know more.

A physics tip: How many types of energy are there?

The previous science snippet introduced the idea of conservation of energy: that for anything to happen anywhere - which always means a change of some type of energy inside a system - then this energy must either be converted from (or to) another type of energy in the system, or transferred to (or from) the system from outside. This is powerful - nothing at all can happen, anywhere in the universe, without it being approved by the 'energy auditors'.

So how many types of energy are there? A web search gives answers ranging from "The 9 types of energy", through "The 7 types of energy" to "The two types of energy". Help!

Well, in science, as in life, the right answer (the most useful and most appropriate) depends on who we're communicating with. So for science-minded folk... nature has only two types of energy: a) energy due to the movement of objects or particles (kinetic energy), and b) energy due to forces between objects or particles (these provide potential energy). A correct answer, therefore, is two. (I am neglecting the cosmos and its still-to-be-figured-out dark energy.)

So what then is 'chemical energy'? Or 'nuclear energy'? Or 'sound energy'...?

Amazingly, each of these energies are made up from only kinetic and potential energies, but are generally due to microscopic constituents. For example, take chemical energy. We may recall from my last post that 1 kg of hydrogen gas releases about 140 MJ of energy when it burns in air. 

So the kinetic energy of all the electrons and nuclei in unburnt hydrogen and unreacted oxygen added to the potential energy due to all forces between these electrons and nuclei give the initial energy of the reactants (the unburnt hydrogen and unreacted oxygen).

Similarly, the kinetic energy of all the electrons and nuclei in the water that is formed, assuming it is at room temperature, added to the potential energy due to forces between these electrons and nuclei gives the final energy of the product (the water).

The difference between these two energies - allowing also for any change in these energies due to this reaction happening at atmospheric pressure (that is, any necessary expansion/contraction of reactant/product gases) - is the energy released as heat. For ease we often call this a release of 'chemical energy', even though it actually derives only from differences in many kinetic and potential energies.

So, in nature there are only two types of energy: kinetic energy and potential energy. We humans find it convenient to lump these into packages. To package or not is up to you - the conservation of energy (provided everything is included) will hold either way.

Finally, a note about Rayf

I generally adopt the spelling Rayf, which is consistent with the pronunciation I prefer, and used by family and friends (/reɪf/). The legal spelling of my name remains 'Ralph', yet this can be confusing in a manner similar to the Stroop effect. Some background to the name, from Ralph Wedgewood at the University of Southern California, can be found here.