Gravity, Momentum and me.



I just recently became mildly obsessed by one of those laws of physics that I (possibly) vaguely understood several decades ago. I need to qualify that statement. A long LONG time ago when I was forced against my better judgement to study Physics prior to college, I realised that equations and ‘laws’ were never going to be my forte. I learned them with a heavy heart, probably wrote a few of them in very small text on my wooden ruler, and entered the exam more in hope than confidence. Writing equations in miniscule text on your ruler was, incidentally, probably the only kind of mild cheating anyone did back then, and evidently it was a hit and miss affair. Mostly you chose the wrong equations, although it did keep wooden ruler sales stable . But I digress.

Many years later, and to my own surprise, I have become mildly interested in this stuff again. And why is that, I hear you ask? Well if it’s due to anything it’s the length of time that one has to ponder the mysteries of life and inexplicable phenomena when on a four hour plus cycle ride. Yes, you idly look at the fellow participants, you may even pass the time of day with them, although I tend to need all my lung power for the hills. You look around at the beautiful landscape, predict the likelihood of that dark cloud turning into driving rain, and you also keep an eye on the people around you lest they launch into an unexpected lurch while your feet are TRAPPED in the pedals. So there’s a lot going on but nevertheless the mind does tend to ramble. And so we come back to the hills, or more precisely what happens on the downslope.

Going up I grit my teeth, tell myself ‘It’s not that far’, try to not end up behind someone going slower, and I grind it out. The crest of the hill is the spot for a heart-rending gasp and a sit-up in the saddle to ease the backache. I may even decide to eat that banana I have painfully lugged up the hill in my back pocket and whose skin I discreetly (with a hint of guilt) jettison because it’s biodegradable. And then it’s physics time.

When I started this cycling lark a relatively short time back, I was very, very, cagey coming down the hills. I kept thinking about how once the front fork snapped, the piece of carbon fibre would pierce my chest as I fell. I thought about the skin grafts I’d need. The years of rehab. I thought about how much my arms hurt as I clutched both brakes with a drowning mans’ grip. In short, I was a wimp. But time changes everything. I’m not exactly Evel Knievel now, but I do tend to ‘let the bike run’ a lot more and reap the dividend for my painful efforts on the other side of the hill. And as I am no longer descending at the pace of a constipated turtle, I have begun to notice something rather odd. I actually come down the hills faster than most people, all other things considered. And this, in turn, plus all that ‘thinking time’ has begun to make me look with fresh eyes at the laws of physics, or maybe even at a few of them joined up together.

My impression is/was that because I’m ‘bigger’ (this covers a multitude) than many of the others around me, I tend to ‘fall faster’. I know there are differences in bikes, aerodynamic shapes and so on, but all other things being equal I believed that big/heavy objects fell faster, due to the law of gravity. And yes, I know I’m not ‘falling’ exactly, but hurtling down a straight hill at 50kph is pretty close in my opinion. So I was more than surprised to discover that I was COMPLETELY WRONG about this stuff. I also discovered that the WWW is literally awash with stuff about physics and merely typing in ‘Do heavy objects fall faster?’ yielded hits on Google reaching comfortably into the thousands. Evidently this is a major playground for moonlighting physicists. Who knew?

And then the names? Even I know that Aristotle, Newton, Galileo and Einstein were heavy hitters. And they ALL have had a piece of the action in their time. Sadly the WWW was not ready for them to share their respective insights, but it seems their disciples are making up for it these days. And what is the overall conclusion, from all of this brain-power?

Well in (this) layman’s terms it seems that a heavy object will in fact fall faster than a lighter one. But – the big equaliser – it seems that conversely the force needed to get the heavy item moving from a standing start is greater than that of the lighter item. So inertia causes the inherently faster object to start slower (my words) and simply cancels out the greater gravitational pull. After a bit, they are both descending at what appears to be about 9.8m per second, and they stay there till they hit the ground. However air resistance does some into this too, so an aerodynamic item (sphere) will fall faster than say a grand piano. They will both make quite a mess if they land on you, but at this point I’d say that was a fairly remote possibility. Incidentally I also discovered that in addition to entire server farms devoted to hosting videos of animals doing crazy stuff, there are – to my astonishment – endless videos on youTube which demonstrate ‘laws of physics’. For reference, the stories about Newton and the apple, Galileo and the leaning tower of Pisa and Einstein and the theory of relativity are all bound up in this, should you decide to spend a wet weekend checking this out on the web…fascinating stuff that I dimly remember.

Now having said ALL this, it’s possible that the law of Momentum is more relevant than the forces of Gravity. Momentum, according to the ever-reliable Wikipedia, is the product of the mass and velocity of an object. This seems to be Newton’s area of expertise again and if you have ever seen one of those weird desktop objects with balls hanging on threads and moving improbably, that’s ‘Newton’s cradle of momentum’. Not just a silly object to while away endless hours.

So back to me on my bike, and the down slope. Why do I go faster than a lot of people? I do have mass (sadly) and when I combine that mass with velocity I do manage to build the momentum quickly. Gravity is less of a consideration, unless I fly off a cliff, which is not in my game plan. So in short, I think I have more or less gotten to the bottom of this unfolding mystery, but I will continue to explore further. It will never turn into a rekindled love affair with physics, but if you have any added scientific evidence to help me reach some definitive answers, I’d love to hear from you. In the meantime I’ll keep rolling, observing and pondering the mysteries of applied physics.



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