Monday, August 2, 2010

Size Relativity

I thought as a second post, I would go into this chapters brief discussions of size relativity, and how it gives moments of when we can really get concepts of size wrong. The first example it provides is in reference to speed. As the example, it talks about how moving at a cm/s is incredibly slow to us (especially since when you think about it, we can quite easily walk at a pace of a m/s), and yet to a bacterium, that is really fast. This concept then gets you thinking about how small a bacterium is. You look at yourself and the components that make you up, and it hits you just how amazing it is that something as small as a bacterium is helping to make up these macroscale components of you, and how in terms of relative size, a bacterium is a much faster, much more work efficient model than a human as a whole (don't confuse that for each component in a person, just as how we as people work in a social environment).
Then, as another example, the chapter reviewed the teaspoon of oil,to display how powerfully tiny atoms can be. This example, just to remind you, was that if you have a teaspoon of oil (around 5 cubic cm) could be spread to its thinnest point without breakage in the surface and cover around 2000 square metres. We always have this knowledge in our heads that atoms are tiny, so very tiny, and that there are a lot of them in even the smallest quantities of product that we hold, but to see such a spread really boggles the mind. When one looks at say a teaspoon of honey, they think that its enough to cover their piece of bread, not their backyard and more. Again, this is a real eye opener to just how powerful out bodies and the environment are, working with these tiny organic machines to perform highly organised tasks.


  1. I wonder how Franklin actually made his observation. 2000m^2 is a lot of area to check for breakages in the oil layer. It also must have been a pretty calm day at the pond for no other factors (e.g. waves, animals, wind) to disturb the oil layer. Whatever he did, his idea was very clever, and reasonably accurate when the molar mass of oil is used rather than water.

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  3. Actually, the bacterium suffers a double whammy. Not only is it small, but the dynamics of its motion are fundamentally different. This is what Nelson was getting at on page 20. No dimensional quantity can be large in an absolute sense, but dimensionLESS quantities can.

    For a bacterium, its small size means a low Reynolds number (Chap. 5). Life at low Reynolds number is qualitatively different, because inertial forces no longer matter. Think about how much distance you require to stop your car. Then consider that the stopping distance of a bacterium is smaller than the diameter of a hydrogen atom! This is a real difference.

    Mind you, the Reynolds number also depends on the properties of the medium, not just the size of the bacterium. A bacterium can travel ballistically in vacuum, as can we...

  4. Talking about relative sizes always makes me think of DNA. I find it amazing that the DNA contained within one nucleus (which is tiny) can actually stretch out to be 2 metres in length.
    This again reinforces the point about how ordered the human body must be.