Pick Peat!

Yes, coffee grounds are fantastic for garden soil or compost.  They’re rich in nitrogen, act as a pH buffer (most of the acidity is removed during brewing), and retain water nicely.  Because coffee grounds are already ground up, they’re easy to mix into your soil or compost, and more easily broken down by worms, bacteria, etc.

All that said, plants need a balanced diet.  Leftover coffee grounds are a terrific addition to your soil, but you probably won’t do well potting a plant in pure coffee grounds.

I will admit some trepidation in attempting to answer this question, because any time you throw “science” and “religion” into a discussion, it tends to get fairly heated.

That said, I think it’s a very important discussion.

So, here are my two cents.

We have an essential desire to know how the universe works.  We’re pushed and pulled towards understanding the world around us, because it gives us peace of mind and the ability to make reasonable decisions about what we do with our lives.

The fundamental goal of science and religion is to address that desire, and I think people who are genuinely interested in learning about the world and humanity will study both.

That said, unquestioning certainty is the biggest thing that keeps us from understanding.  The unquestionable idea is both poisonous and tenuous — poisonous in that it isolates people and sets them against each other, and tenuous in that all theories and beliefs are eventually tested.  When a theory holds true, it is no longer unquestioned — if it is not, it gets discarded for something better.

This pattern has has repeated itself for as long as we’ve been around:  The landscape of human history is littered with the remains of failed ideas.  It takes time, sometimes thousands of years, but when we’re empowered to ask questions, we start to see and move beyond our failed ideas.

I think it’s reasonable to believe that this trend will continue.  

The “battle” between religion and science is short sighted.  Extraordinary scientific progress has come from deeply religious cultures, and it bothers me to see so much time and energy wasted on polarizing questions that can only be advanced by thoughtful, attentive, and reasonable discussion.

The place of religion in science (and science in religion) is to work towards discovering the truth about who we are, where we are, and why we’re here.  The goal is to improve ourselves and the world around us.  The goal is to lead fulfilled lives, to have adventures, to play games, to connect with others, to learn — to do the things that we love to do.

That’s my theory, anyway.

You’re welcome to ask why!

I think you asked this just to see some awesome videos.

An explanation will follow!

… and who doesn’t like Ellen?

Alright, alright, that’s good enough. You get the idea — it’s a vaguely creepy goo, and you can make in your own kitchen!

Simply stated, a fluid is non-newtonian if it’s viscosity changes under stress (like a punch, or vibration from a speaker).

Cornstarch is a particularly fun and cheap demonstration, and silly putty does the same thing.

But why?  

In “normal” newtonian fluids, when you put pressure on the fluid the molecules can slip past each other at a rate that’s constant with the pressure.  When a non-newtonian fluid is put under pressure, the molecules have trouble flowing past each other and lock up.  It requires a certain density of molecules to work, otherwise they can’t get close enough to connect.

You can experiment on your own: take a bowl half full of warm water, and slowly add cornstarch.  It’ll slowly thicken up, but it doesn’t start acting strange until cornstarch makes up about 1/3 of the volume of the mixture.  The effect will gradually increase, and when cornstarch makes up about 2/3rds of the mixture, you’ll have a pretty fantastic substance to play with!

People have been trying to figure out the physics of light for a long time: the double slit experiment is over two hundred years old, and the fundamental problem of whether light is a wave or a particle has been argued since 400 BC.

The problem is pretty straight forward.  Consider a baseball player whacking a fly ball into the outfield:  everyone experiences the sound of the bat smacking the ball — that’s the sound wave, spreading through out the stadium.  On the other hand, the ball behaves like a single “thing” — it stays in one piece and follows a graceful arc into the glove of the outfielder, instead of spreading like a wave.

The reason the double slit experiment is so intriguing is that it demonstrates that light behaves like a wave and a particle, which is pretty dang counterintuitive if we think about the problem in terms of sound or baseballs.

Here’s a thought experiment:  If you fire a bunch of identical photons at two small slits cut into a screen, and look at the pattern that emerges on the wall beyond, what do you think you’ll see?

If you think of light as a particle, you’d see two bright dots on the wall.  After all, if you threw a baseball, it would pass through the hole and straight on to the wall behind.  Split the baseballs between the holes, and voila: two piles of baseballs … or in the case of photons, two bright dots on the wall.

If you think of light as a wave, you’d see a smear of light: the light wave would pass through both slits and spread out like ripples in a pond, a process called diffraction.  You might even see some patterns in the smear if you think about wave interference between the two slits.

And what actually happens is … all of the above.

If you send a single photon to the screen, and put a dot at where it hits the wall beyond, it will land in a single spot, just like a baseball.  But unlike the baseball, it probably won’t be in line from where you fired it.

Weird.  Lets fire another photon.

It’ll do the same thing, but land in a different spot.  Possibly quite far away from the first.

Keep on firing photons, and you’ll start to see a pattern emerge on the wall … and the pattern looks exactly like the interference pattern you’d expect to see for waves passing through those slits.

Ok, cool.  So, somehow the photons get redirected while in flight to form what looks to be an interference pattern.  But how is that possible?  We’re only firing one photon at a time, so it’s either passing through one slit or the other, right?  Interference comes from two waves interacting, so that means the light has to be passing through both slits — which is only possible if it’s actually a wave hitting both slits at the same time.

Maybe it’s not an interference pattern?  What happens if you cover up one of the slits?  That pattern disappears — so we can reasonably conclude that it really is an interference pattern produced by a light wave passing through both slits simultaneously.  In fact, we can prove it is interference, based on the frequency of the light and the pattern of bright and dark bands.

But wait, weren’t we firing single photons?  Single photons that pass through both slits in the screen simultaneously?   And end up as single points of light on the wall beyond, but organized into an interference pattern from intersecting waves?

Yes, yes, yes, and yes.

Behold: the strange glory of quantum mechanics, and particle-wave duality.  

It turns out that all of the major subatomic particles behave like this — photons, electrons, neutrons, and protons.  There have even been experiments with molecules that exhibited wave-like properties (like diffraction), including fluorinated fullerine, a relatively huge molecule with 60 carbon atoms and 48 fluorine atoms. 

There are still significant debates about the mechanism that causes particle-wave duality, but no doubt that we can see it in action.

Granted, it’s not something we see every day, but when you think about the fact that it’s real and verifyable, there’s nothing “spooky” about it.  There are no laws being broken, or supernatural powers involved — it’s just not something we expect.

Kind of like a surprise party.

That’s how I like to think of quantum mechanics:  it’s the biggest surprise party ever thrown for the physics world, and everyone’s invited.

(image courtesy of Dr. Tonomura and the Wikimedia Commons)

This is a great example of an old fashioned measurement system that is still clinging to life in the modern era, despite the fact that it’s hard to use, difficult to understand, and inaccurate.

So this should be fun!

Here’s the deal.  Back in the 1800s, the first real bicycles were horrifying contraptions, aptly nicknamed “boneshakers.”  Imaging cruising around the cobblestone streets of London on a bike that weighs fifty pounds, sporting iron (!) wheels.  Not such a great experience, eh?

Regardless, it was the state of the art at the time, and one of the things people were concerned about was how far the bicycles would travel with one turn of the pedals.  Since the pedals were fixed to the front wheel, one turn of the pedals produced one turn of the wheel.  Smaller wheels pedaled easier, but didn’t travel far.  Larger wheels were harder to turn, but took you further.

The measurement that people bantered about was the diameter of the wheel, measured in inches.  On some of the penny farthing bicycles the front wheels where over fifty inches, and were raced by would-be Lance Armstrongs on tracks at a whopping fifteen miles per hour.

Over the last hundred years, bicycles have evolved.  We’ve added gears and standardized wheel sizes, which really throws off the notion of using the size of the wheel for determining the ratio between pedaling and distance.

Never the less, human ingenuity has bent, broken, and resuscitated this notion of wheel inches into gear inches, which converts a gear setting on your modern bicycle to the diameter of a fixed wheel from an iron beast from the 1800s.

So, here we go!

Today, you can calculate your gear inches as follows:

• Gear Inches = Wheel Diameter x (Front Gear Teeth / Rear Gear Teeth)

Dividing your front gear teeth by the rear gear teeth gives you the ratio of how your pedaling is modified by your gearing, so you simply apply that to the diameter of your wheel and you’re good to go.

Working in metric?  Hold on to your top hats.  Europeans use a completely different (and similarly inaccurate) system called “meters of development” which measures how far your bike travels with one turn of the pedal.  To convert, multiply the gear inches by pi, and convert to metric units.

So why do I keep saying inaccurate?

The problem is that both of these measurements completely miss an important variable:  the length of the arms on your pedals (“crank arms,” as cyclists call them).  The strength required to heave you bike up a hill is directly related to the ratio between the distance your feet travel and the distance the bike travels, and if you lengthen your crank arms, you change that ratio.  In other words, you can have completely different gear inch measurements that require the same amount of strength and go the same distance because of different length crank arms.

If you want to compare your carbon fiber and titanium superbike to a iron wheeled boneshaker from the 1800s, go ahead and use gear inches.   If you’re interested in the real relationship between your feet and your bicycle, use a measurement called “gain ratio:”

• Gain Ratio = (Wheel Radius / Crank Arm Length) * (Front Gear Teeth / Rear Gear Teeth)

This accounts for all of the components on your bicycle that effect how hard you’re pushing when you’re rolling down the road:  your gearing, the size of your wheels, and the length of your crank arms.  As a bonus, it’s expressed as a ratio, which needs no conversion whether you’re measuring in metric or imperial units!

Next time someone asks you about gear inches or meters of development, I encourage you to politely bring them into the 21st century.  Gain ratio is where it’s at — even if you’re racing boneshakers and penny farthings!

Riding a wave is a sweet mix of buoyancy and planing.

Buoyancy is all about displacement and density.  I think the best example of buoyancy is an ice cube floating in water.  Ice and water are made of the exact same molecules, but pound for pound, ice takes up more space.  When you place an ice cube in a glass of water, the ice cube will sink until the weight of water it displaces is equal to the weight of the ice cube, and since ice takes up more space, the “extra” volume of ice stays above the surface of the water.  In other words, ice is less dense than water, so it floats.

The only requirement for floating in the ocean is that you have to be less dense than ocean water.  Here’s how the 200 pound surfer with a little chunk of foam plays out:

• A cubic foot of sea water weighs about 64 pounds.
• A cubic foot of foam weighs about 2.5 pounds.
• The buoyancy of a cubic foot of foam in sea water is 61.5 pounds of lift (the difference between the water and the foam).
• To float a 200 pound surfer, we need about 3.25 cubic feet of foam.

So that’s all well and good if we’re just sitting in the water.  But what about all those killer videos of surfers slicing down the face of a wave, barely touching it at all?  How does that work?

That’s where planing comes in.

Planing is what happens when a surfboard is moving fast enough that the force of the water pushing against it exceeds the force of its buoyancy.  The faster the board is moving, the stronger the effect.  Think about water skiers.  They barely float when they’re sitting in the water, but quickly rise to the surface when the tow boat takes off: the force of the water pushing against the skis is enough to lift the rider out of the water.  Surfboards operate on the same principal, but instead of being towed by a boat, they’re accelerated by “falling” down the face of a wave.

You could, in theory, surf with a board that’s heavier than ocean water if you were towed into the wave at a high enough speed … But it wouldn’t be nearly as much fun!

(photo copyright Justin Myers)

Skate wheels have to deal with some pretty rough treatment, including hard impacts, and gripping or skidding over concrete under your full weight.   Additionally, skaters have different needs for different surfaces and skating styles. 

For example, a vert or park skater will want very hard wheels.  They roll fast on the smooth concrete and wood ramps in a skatepark, and slide more easily than soft wheels, making it easier to do tricks.  On the other hand, street skaters sometimes want slightly softer wheels to help absorb the roughness of asphalt, and to get more traction on the road.  Hard wheels are louder, soft wheels are quieter.  There are a lot of trade offs, and almost every skater has a different take on it.

Urethane (a.k.a. polyurethane) is almost perfect for the job — it’s inexpensive, easy to work with, incredibly tough, and the softness can be easily adjusted.  Most other plastics just aren’t up for the task, or are so exotic they’d be too expensive.

The process of manufacturing a wheel is pretty straight forward:

• Several polyurethanes and other ingredients (like colors and curing agents) are mixed and melted together, according to a recipe.  The combination of different polyurethanes is what gives a wheel it’s characteristic hardness and durability, so a wheel manufacturer will have several different recipes for the different styles of wheel they produce.
• The hot mix is injected into a mold, and hardens as it “cures.”  It’s kind of like baking a cake: the curing process is a chemical reaction that happens when all the ingredients interact and cook together. 
• When the wheel is done curing, it’s put on a lathe that trims it down and finishes the surfaces:  the seat for the ball bearings, the smooth sidewalls, and the lightly textured rolling surface.
• Finally, graphics are applied to the wheel to dress it up a bit.

Tada!  A urethane skate wheel is born!

So, what about recycling?  

If you’re an environmentally conscious skater, this is a problem.  Most skaters will replace their wheels after they’ve worn down a few milimeters — wheels don’t always wear evenly, and they’re unpleasant to ride when they develop a flat spot.   The end result is that you end up with a pretty big chunk of urethane that isn’t useful anymore … and wouldn’t it be nice if it could get recycled into other skate wheels?

There are a few forms of recycling, but in most cases it’s just too expensive to do.

Complete recycling of the urethane in a wheel requires it to be broken down into reusable chemicals, which is quite difficult.  It’s like unbaking a cake:  because urethane wheels are cured, the ingredients have been changed at a molecular level.  If you attempt to melt a wheel down, you’ll change the chemical structure and it won’t be reusable for skate wheels.  In fact, you’re more likely to burn the urethane than melt it if you try it on your own.

There are other ways to recycle urethane, though. In some cases, it can be cut up for use in fish habitats, used in asphalt, other other “green” disposal forms.

One of the cooler recycling programs I’ve seen takes an old wheel, cuts it down, and uses it as the core for another wheel.  It’s like a retread truck tire (where they just wrap a new rubber tread around an old, worn down tire).  There’s still waste in the lathing process, but it’s about as direct of a recycling program as you can get.

There you go:  why we use urethane, and why we have a hard time recycling it.

The chemistry of urethanes is a continually growing and improving science.  There are people who are working right now on solving this problem, and I’m excited to see the day when the recycling question is easily answered.