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Updated January 22, 2016 | By Bob Fugett

Simple Physics

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Don't get scared, this ain't hard.

Here is a fact: a 20 mph pace takes less force on the pedals than is required to grab a full bicycle water bottle off the floor and place it on a table.

Totally disregard the blue rectangle below because we are not going to use it anyway. It is just here to show you the kind of stuff we are NOT going to talk about. You and I have no interest in blowing up cities.

Click to see where I stole this.
Click to see where I stole this.


Otherwise, there are a few simple concepts of basic classical physics which make the entire world (...hell, the entire universe) easy to understand and predict.

Classical physics is the stuff about how things move around you, without all the math and gibberish like in the blue rectangle above.

You know, stuff like: you drop a ball, and it bounces off the floor, and it always will bounce off the floor—and exactly the same way if you drop it the same way.

Therefore, if you drop the ball from a specific height, it will always bounce back just exactly an exact specific height, exactly the same way every time.


In fact that height is so predictable you can bounce it off the floor again and again even while running around a room not even looking at it, then throw it just so, and way over yonder swish... through a hoop.

You know, stuff like that.

You might want to know these things because if you never get around to learning the most basic literal facts about how objects in the real world behave, you leave yourself open to an incredible amount of deceit foisted on you by purveyors of magic, myth, and expensive bicycles.

Stuff like, "Oh, look, there's a quarter behind your ear..." or, "They don't look and talk like you do, therefore they are total fucking evil bastards, rotten to the core. They are coming after you, and they deserve to die," or, "You really need this little doohickey on your bicycle in order to go fast. It is expensive, but you are worth it. You want to win, don't you?"

Stuff like that.

Otherwise, if you are familiar with the following few concepts the world is your oyster... especially if it is the world of cycling.

Knowing these things can help you beat just about anybody who doesn't know them.

Here is the first thing you should know.

inertia - inertia means that things tend to stay just exactly the way they are, either in motion or at rest. An outside force of some sort is required to change either situation.

If something is not moving, it takes force to move it. On the other hand, if something is moving, it takes force to stop it, and it takes exactly the same amount of force to stop it as it did to start it.

Think about that for awhile, look at the things around you, and guess what all this means for you on your bicycle.

Here are two things it means (I did not make this up):

1) If you get your bicycle moving, it doesn't want to stop. Not only does it not want to stop, it doesn't even want to slow down... at all. Something has to happen to make it slow down and stop.

Doesn't that make you happy? If you get your bicycle going at 23 miles an hour, it will stay going that way forever. All you have to do is avoid the things that would make it slow down and stop (such as brick walls), and it is just exactly as hard to make it slow down and stop as it was to get it going in the first place.

The thought of that gets me pretty excited, except for the part about the brick wall.

2) On the other hand, if your bicycle is not moving, it doesn't want to start moving. Not only does it not want to get going fast, it doesn't want to get going at all. In fact, it takes just as much force to get it going only a little bit faster as it does to get it going to the speed of light.

Doesn't that make you happy? You don't need any more effort to get your bicycle going really fast than you do to just get it going at all. The thought of that also gets me pretty excited.

You can get your bike going can't you? Then you can get going as fast as there is. There are a couple minor problems, but they affect everybody the same way, so you can deal with them.

Here's a little math problem. It is just addition, subtraction, and division stuff, so not hard in the least. Besides I am giving you the answer right after the question, so at least try it:

Question: Discounting air and friction (hills don't matter at all), if you are on your bike going 20 mph, and your speed is increasing the smallest amount possible, let's call it spinning a 100 watts, how many more watts will you need to reach 23 mph?

Answer: None.

That answer (None) sounds improbable, but I've done it a few times to prove it myself.

You can think about that for awhile if you like, but it is absolutely true, so I am moving on to something else.

Oh, I almost forgot. You might be wondering what force is.

force - force is pow, pop, bang, zingo, and that about covers it as good as anybody ever has.

Remember I said there are a couple minor problems to deal with: the first problem is that the air likes to keep you from going really, really fast.

Actually, the air likes to hold you back harder and harder, the faster and faster you go.

 The math word for that is logarithmic, or maybe somewhat parabolic, but I promised there would be no gibberish here, so forget those words.

Just remember this: the harder you push air, the more pissed off it gets and pushes back harder and harder the more harder you pushed it back first.

No, that was not a misprint. Read it again more slowly.

Now to prove to yourself that this whole air pushing back harder thing is true, you will want to experience it first hand, and that is easiest to do if you trap a significantly smaller amount than is outdoors and push it around where you can watch.

Best way to trap some air is by getting one of those big gymnasium instability balls of the kind girls like to sit on pretty and pretend to be working out, and fill it with about as much air as it will take.

Then put it on the floor and push down on it.

You will notice that if you push down very lightly the "air" moves away from your hands very quickly and easily, but the harder you push it, the more it pushes back until finally you could put your whole weight on it and it wouldn't budge.

Don't worry, those balls are made to take your full weight and not pop: just don't fall off, because it's not so easy as all those girls sitting pretty make it appear.

Other than air, nothing except the friction of your bicycle parts plus wheels on the road will do anything to slow you down, and those things have been so cleverly avoided by all but the most clumsy of modern bicycles, you only have to worry about them if your goal is to win a 3 week race over 2,100 miles long, and even then it is questionable if anything is really going to make much more than a few seconds difference over the whole course.

Just get hard skinny tires for the road and big knobby ones for rock trails. 

Below is a graph that shows you how the air outside likes to make it harder for you to go faster, and how the harder you go harder the more harder it likes to make it more harder for you to go more faster.

Once again, that was not a misprint. You will just have to accept the slight error in grammar, because like I said, there is a mathematical term for what it describeslogarithmic, but you don't need to know that term and should try to forget it as soon as you can. If you use a word like that, people will think you know something, and they won't let you go on a ride with them.

Otherwise, you might like to be aware that all this stuff (inertia, force, air resistance) works out best for you on a more or less circular route beginning and ending in the same place—which by the way takes care of the hills along with the air resistance (what some people like to call wind).

Anyway, here's the graph:

abstracted from: Firth, Malcom. "A Look At Time Trial Pacing Strategy"

Did you notice the little target just past the 23 mph mark for the Widder to think about?

See the numbers going up the left side?

Those are the numbers from your power meter (watts). All you have to do is get your meter showing those numbers, and the numbers across the bottom (speed) will take care of themselves.

This book is not called Cycling Performance Simplified for nothing.

The bend in the line on the graph shows just how hard the air likes to push back on you depending on how hard you are trying to push on it.

If you don't like math, you can have your numbers worked out for you by my online calculator which tracks well with the chart above based on you putting in only your watts and weight. It also calculates your Race Category and is called the Super Simple Power to Weight Calculator.

Hills have no effect. They just go up and down exactly like the bouncing ball described previously and cancel themselves out, so there is a whole chapter about how there are no hills.

There is also a chapter about how there is no wind, because there is far too much air (more than 75 miles it just over your head) for you to be worrying about a little thing like wind.

A headwind will become a tailwind (or the reverse) somewhere about half way through your loop.

Got it? Good.

See? That wasn't hard... weird maybe, but not hard.

Get your bike going and it won't want to stop, give it a little more juice (patiently) and you can get it going about as fast as you like.

Remember: a 20 mph pace takes less force on the pedals than is required to grab a full bicycle water bottle off the floor and place it on a table.

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