Rayf Shiell - Optical Physics Group, Trent University

Miscellaneous: Aug 2022

Hi! Here you'll find this month's fun science snippet and a physics tip, and at the very end a brief note about my name.

(Click here for science snippets and physics tips from previous months)

Snippet from science: 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 speeding-up, from glacial changes 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 for sure.

Tip for physics: How many types of energy are there?

Last month's science snippet introduced the 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 remarkably powerful - nothing at all can happen, anywhere in the universe, without the 'energy cops' allowing it.

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 (namely, most useful and correct for the intended purpose) depends on who we're communicating with. So for science folk out there... nature has only two types of energy: that due to the movement of objects or particles (kinetic energy), and that due to forces between objects or particles (these provide potential energy). A correct answer, therefore, is two. (I'm neglecting here 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 from only kinetic and/or potential energies, but generally of the microscopic constituents. For example, take chemical energy. We may recall from last month that 1 kg of hydrogen gas releases about 140 MJ when it burns in air. 

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

Similarly, the kinetic energy of all electrons and nuclei in the water that results added to the potential energy due to all forces between all electrons and nuclei in the water that results gives the final energy of the product (the water that results).

The difference between these two energies - allowing also for any change in kinetic energy and potential energy due to this reaction happening at constant atmospheric pressure (that is, any necessary expansion/contraction of the product gas) - is the energy released. It's often easier to call this overall difference the difference in 'chemical energy', even though it actually comes only from lots of kinetic energies and potential energies.

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

And, a brief note about 'Rayf'

Some time ago I adopted the spelling Rayf, which is consistent with the pronunciation I prefer, and that used by family and friends - namely /rf/. The legal spelling remains 'Ralph', yet can be confusing in a manner similar to the Stroop effect. Some history of the name, compiled by Ralph (/rf/) Wedgewood at the University of Southern California, can be found here.