Unit (part 1)

For some, Physics is a subject too hard to grasp. The reasons for this vary from individual to individual. Some were taught by teachers (though knowledgeable and resourceful) who failed to transmit the essence of Physics across to the students. Others failed to appreciate the relevance of Physics even though they were taught by dedicated and passionate teachers who could translate the beauty of Physics from the dull, drab textbooks into wonderful lectures and laboratory demonstrations. This means that, for a student to understand and appreciate Physics, there needs to be a teacher who knows how to prepare the mind of such student so as to receive that knowledge. For we can’t expect a tree to blossom if we sow the seed in unprepared soil. By simply depositing the knowledge and expecting the students to cultivate that knowledge is not only wrong but dishonest. The good thing about the preparation is that it makes teaching easier. For if the students have been prepared to receive that knowledge then they will be able to nurture that knowledge on their own with only minimal guidance from the teacher. So how to prepare the mind for Physics?

Physics: a whirlpool of concepts in an organised system

I think the simplest method is to leave the textbooks alone for at least a couple of sessions. The tendency to immediately jump to what’s been prescribed and plunge the students into a very rigid and academic framework, so as to get started with the syllabus, is what creates this barrier in the students’ minds; a barrier that comes up as some sort of defense mechanism, an alert mode, an apprehensive mind that thinks that, if I don’t get this then I won’t get good results. This mindset is what stops the students from easing in to the subject. Teachers should gradually introduce the subject as opposed to rushing through the notes. This is the most important step in teaching. Just work the students’ mind, massage it, knead it, prep it so that they warm up to this new idea, this new concept, this new subject that they are about to receive.

We see tennis players pump the balls before they serve; they bounce it off the ground a few times, working the ball, pumping energy into it, warming it up. It only helps to make a better service and, possibly, an ace. The same principle, by the way, happens on a much larger scale. Jupiter and its sixth closest moon, Europa, exist in what we call a tidal flexing mode. As Europa orbits Jupiter along a somewhat eccentric path (i.e., Europa doesn’t quite go round Jupiter in circles but rather in a shape we call an ellipse – a ‘flattened circle’ in simple terms), sometimes it’s closer to Jupiter, sometimes further away. As it gets closer to Jupiter, it’s pulled in towards Jupiter with an even greater force of gravity than when its further away. And because Jupiter exerts such a tremendous force, it is able to distort Europa ever so slightly so that Europa no longer assumes this spherical shape but becomes this egg-shaped moon. As Europa then moves further away from Jupiter, it relaxes back to its more spherical shape. This continuous reshaping of Europa is similar to the bouncing tennis ball. And just like the tennis player pumps energy into the bouncing ball, Jupiter pumps energy into Europa. This is what we call tidal flexing. The bulging in and out of Europa. But that’s not the end of the story; this pumping of energy into Europa doesn’t go to waste. It actually keeps the inside of Europa so warm that there could very well be liquid water underneath the icy surface of that moon! And where there is water, there lies the possibility of life. Please refer to my blog Juice to see how this exciting possibility is being investigated. So, to cut a long story short, there needs to be this tidal flexing between teachers and students so that students can warm up to this new subject and so that teachers can transmit this knowledge. The rest will almost definitely take care of itself.

One of the very first things we are taught about Physics is a list of physical quantities. We learn about time, mass, temperature, etc. Rather than simply presenting this list of physical quantities to the students and expect them to memorise the different symbols and units associated with them, the teacher should take some time to weave this story about where those quantities come from. They should explain why we have such a list to begin with. It might sound trivial but without showing the relevance of that list, none of the students would ‘lock in’ with this idea. The story serves to prep the students and warm them up to understanding the different physical quantities. So what are they anyway? And why should we even bother learning about them?

Perhaps the most relevant and intuitive of physical quantities is time. By the way, whenever we speak of physical quantities we mean that there is some characteristic of the physical world that we can observe and measure. Whatever we can quantify, or put a number to, is called a quantity. So, time is perhaps the most intuitive of all. We all experience it, we all relate to it, we all can tell what it is. Time is easy. But we might not all agree on it, however. What feels like minutes to someone can be only a matter of seconds to someone else. Our mood plays a lot on our perception of time. So we can’t rely on ourselves to properly quantify it. We need a standard method to measure the interval between two events. Whether these events are, say, two consecutive sunrises, in which case we have the definition of a day, or whether it is the duration between two full moons, in which case we have the month, we need some objective way to measure time. Now, objective does not necessarily mean accurate. A day is not precisely 24 hours. Full moons are not exactly 30 days apart. So, besides an objective way to measure time, we also need an accurate and reliable method to keep count of it. The same applies to any other physical quantities by the way. We need some standard and accurate and reliable and reproducible way to keep track of all those quantities and make sure that we are all referring to the same quantity no matter where we are or what season we are in. One such standard is called the International System of Units (abbreviated to SI from Système International d’unités). In that system, the fundamental unit of time is the ‘second‘. Every tick and tock of the clock are a second apart. But clocks, as we all know, are not very reliable. Some slow down others go faster. It’s hard to find two clocks that always tick in time without one lagging behind. As such, we rely on something else to give us that duration of a second. All the clocks are based on the second as given by a peculiar property of some atom, called the caesium 133 atom. Without going into too much detail for now, it suffices to know that, in some conditions, this atom emits a certain kind of radiation, a certain type of light, if you will. And this light has the characteristic that it vibrates a given number of times. (For more on light and vibrations and waves, please see my blog Spectrum.) The vibrations are so accurate, in those strict conditions, that we can use them as our definition of the unit of time called ‘second’. The second lasts as long as 9 192 631 770 vibrations of that radiation. Somewhat like the day which lasts as long as the interval between two consecutive sunrises, the second lasts as long as 9 billion-or-so vibrations of that radiation from the caesium atom. We can keep on talking about time but, unfortunately, we don’t have the time for that. That said, the first thing to learn is that time is perhaps the most fundamental of the fundamental quantities and we count it in seconds. Every other units of time are based on the second. A minute is 60 seconds, an hour is 60 minutes etc., etc.

The second quantity which we can all relate to is space. We move in it. We live in it. We take up space. We rent it, we buy it, we sell it. Whatever it may be, we all know what space means. By the way, space and time are really one and the same quantity – it is a hard concept to grasp, fair enough. But Einstein has shown, rather elegantly, how space and time is just one physical property of our Universe. The spacetime continuum permeates all of our Universe. The distinction between space and time, however, exists in our minds. It is how we perceive that spacetime continuum that makes it look like it is two separate things. But that’s fine. We can deal with this. And it doesn’t mean that we’re doing it wrong by considering them as two separate quantities. It just makes things easy for us to handle. Anyway, space. That’s got to do with distances. The further away we are from something the bigger the space separating us. And length is simply the distance between two things; the distance between two points. If time is the duration between two events, length is the distance between two points. Even here we can see how easy it is to reconcile those two quantities into one. But that said, spacetime is slightly more nuanced than that. We’ll leave that for later. So length is another fundamental quantity. And just as with time, there is a standard way to measure length. The SI unit for length is the ‘metre‘. Again, we are all familiar with that unit of length and its derivatives. We deal with centimetres, metres, kilometres on a daily basis. These are things we can relate to, easily. But the metre, itself, cannot be defined according to the distance between the ends of a rod, for example. The concept of length, as Einstein has shown, is not constant but flexible. Depending on how fast a person is moving, the distance that person perceives as a metre can be different relative to someone who is not moving at all. That’s something that’s been explained by Einstein in his Special Theory of Relativity and has to do with the phenomenon called Lorentz Contraction. As such, the definition of the metre is not associated with length but, interestingly enough, with time! Now, there’s one thing we know that doesn’t change at all. It’s the speed of light in vacuum. It always travels at a given, definite speed in vacuum. And so, using this as our reference, we define the metre as the distance light travels (in vacuum) in 1/299 792 458 of a second (or about 0.000000003336 second). The second, as we’ve shown earlier, is itself defined according to a set number of vibrations. And because these vibrations do not change and because the speed of light does not change, the second and, as a consequence, the metre have an exact and reliable and constant definition. And everybody is happy. Except that this is not the end of the story. There are other things in the Universe apart from the spacetime continuum.

CONTINUED in Unit (part 2)


One thought on “Unit (part 1)

  1. Pingback: Unit (part 2) « electrolights

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