Everything is a voltage

OK, well not everything, obviously.  However, our lives are permeated by electronics: not just cell phones and laptops, but garage door openers, coffee pots, earbuds, traffic lights, thermostats.  Understanding how voltages control just about everything we use was quite the “light bulb” moment for me.  

First off, what exactly is a voltage?  It’s easiest to think about voltage as a hill – sort of like the hill we were biking down in the last post.  Electricity is carried by electrons.  An electron can be thought of as a ball (a very tiny one, of course), which wants to roll downhill.  The bigger the voltage, the bigger the hill that the electrons will roll down.  In fact, you may have heard the term “ground” used in reference to electrical circuits.  Just as an actual ball falls to the ground when dropped, an electron will “fall” towards the voltage ground.  A battery does the work of carrying that electron to the top of the hill and pushing it down.  So an electron pushed “downhill” by a 9-volt battery will carry more energy than an electron pushed by a AA (1.5-volt) battery.  

Electrons travel around a circuit towards the voltage ground, just as a ball rolls down a hill.

Using electrons for electricity requires pushing lots of them downhill.  Or, more accurately, through an electrical circuit.  When pushed through a circuit that contains a light bulb for example, the energy that the electrons carry can be used to produce light.  When a signal of one type is converted to a signal of another type, we physicists like to say that it has been “transduced.”  In the case of the light bulb, we transduce electrical energy to light energy. 

Transduction can happen in both directions.  Instead of converting electrical energy to light energy, as in a light bulb, there are sensors that go the other way, converting light energy to a voltage.  A lot of new-ish cars now have such sensors in order to detect light and determine if it’s dark enough outside to require headlights.  The sensor then sends a voltage to operate a switch that controls your headlights.  And you can convert more than just light energy to or from a voltage.  A microphone transduces sound energy into a voltage.  This voltage is sent through cables, possibly amplified, and transduced back to sound energy at the speaker.  Sound energy to voltage, and back to sound energy.  

All this talk about converting light and sound energy reminds me: biology makes use of voltage signals too.  In fact, you can think of your eyes, ears, fingers, tongue, and nose as transducers.  Your eyes take light in, and transduce it to a voltage.  This voltage signal is sent via your optic nerve (think electrical wires) to your brain, where the voltage signal is interpreted as an image.  Your ears are just like the microphone – they take pressure waves in the air and transduce it to a voltage which your brain interprets as sound.  This insight changed the way I experience live music.  The energy in the singer’s voice is converted many many times – sound to voltage at the mic, back to sound at the speakers, to ear drum vibrations, to neuron signals – all before you experience it as music.

All of your senses are mediated by voltages.  Everything gets converted first to a voltage in order for your brain to process it.  It works the other way too.  Let’s say you wanted to run, bike, or swim.  Your brain sends voltage signals to your limbs, causing your muscles to contract and your limbs to move.  A triathlon wouldn’t be possible without voltages.  

Another useful concept in electrical circuits is the switch.  We are all very familiar with the light switch.  But switches are so much more ubiquitous in everyday life than just the light switch.  Anything with an ON/OFF button has a switch, sure.  But the left and right mouse click: those are switches too.  So is every button on the TV remote and every key on your laptop keyboard.  Switches allow us to control the flow of electricity.  A voltage will push electrons around a circuit only when the circuit is a complete loop, as in the light bulb cartoon below.  

 

A switch is used to control whether a voltage pushes electrons around a circuit.

Using a switch, you can also use voltages to push electrons over long distances in order to send messages.  This is the premise of a telegraph.  At one end of a telegraph line is the sender.  He or she presses a switch in a sequence of long and short pulses to encode the message.  That switch closes a circuit, allowing electrons to flow all the way to the receiver.  At the receiving end, those electrons are used to turn on a light bulb in the same sequence of short and long pauses.  While watching the light bulb flicker, the receiver decodes the message.  (Instead of turning on and off a light bulb at the receiving end, a speaker or buzzer was often used – accounting for the familiar beeping noise we associate with telegraphs). 

Telegraphs are ancient history though.  Who cares?  Well, the principle of sending messages hasn’t really changed a lot since then.  The message you send in an email is transduced first by your keyboard to a series of voltage pulses.  These pulses are sent to the computer, were they are again transduced – they can be converted for saving on your hard disk, to pixels on your monitor, or sent along again as voltage pulses across the internet through the cables provided by, well, your cable company.  At the other end, those voltage pulses are interpreted by the receiving computer and again transduced to pixels on a screen to display the letters of the message.  

Between switches and transducers, you can interact with and control just about anything.  That’s why I was so excited about this week’s project at www.donorschoose.org\sciathlon – “Electrical Inventioneering.”  I’ve chosen to highlight this classroom in Illinois because it will get high school students using their own hands to learn how signals can be converted to and from voltages.  They will be building electronic circuits using a really cool circuit board called Arduino.  The Arduino is all about transduction: “Arduino senses the environment by receiving inputs from many sensors, and affects its surroundings by controlling lights, motors, and other actuators.”  I believe the chance to build such circuits will change the way these students view the gadgets they use every day and may even spark ideas for how we can use technology to improve lives.  I hope you can help me make this happen!  As always, thanks for your support.

Galileo and the two cyclists

Most people have heard of Galileo’s (alleged) famous experiment where two cannon balls – one heavy, one light – were dropped from the Leaning Tower of Pisa.  Which one hit the ground first?  Why not try the experiment yourself?  Find two rocks of different weights, and drop them at the same time from the same height (safety first!).  What do you observe?  The two objects hit the ground at the same time.  

There are two things you need to know to understand why this works.  The first is that bigger objects require more force to get them moving.  This is probably intuitive.  A baseball is easier to throw than a bowling ball.  The second physics principle at work here is gravity.  We all think of gravity as the force that pulls objects down to the ground.  Well, this force gets bigger for bigger objects.  So the heavier rock gets pulled to earth with more force.  But since it also took more force to get that big rock moving in the first place, it ends up falling no faster than the small rock.  Said another way, both rocks fall with the same acceleration – their speed increases at the same rate.

After learning that “all objects fall with the same acceleration”, an always curious and ever-incredulous student (the best kind) asked me, “so why does a heavier cyclist roll down a hill faster than a lighter one?”  It’s a good question, to which I couldn’t provide an immediate answer.  We just learned that gravity causes two objects, regardless of their mass, to fall at the same rate.  This should be true whether you are a rock falling straight towards earth, or a cyclist rolling down a hill.  So what gives?

Galileo wasn’t wrong.  It’s just that his model of falling objects was incomplete.  This is often the case in physics and all of science.  As Einstein once (maybe) said “Everything should be made as simple as possible, but no simpler.”  In other words, if the simple model works, great!  If not, we need to modify it in order to get a better description.  

Applying Galileo's model of the falling rocks to the two cyclists is too simple – it considers only the force due to gravity as affecting their downhill motion.  What else is pushing or pulling on the cyclist?  Well, at least so far, all cycling races take place on earth, where there is air.  This is mostly good of course: no cyclist could make it very far without air.  But air also creates air resistance, or drag.   So while gravity pulls the cyclists down the hill, the force of drag pushes back. 

The forces of gravity and drag compete when a cyclist rolls down a hill.

With Galileo’s experiment, we saw that the acceleration from gravity is mass-independent.  Not true for drag.  A given amount of drag force is less effective at slowing down a massive rider than a light one.  If you instead try Galileo’s experiment with a feather and a rock, you will see this principle quite clearly.  Drag has a huge impact on the feather (both because the feather’s mass is small, and the drag it experiences is large), causing it to drift slowly to the ground.   Taking gravity and drag into account, we can look at the speed of two riders over time as they descend down a hill.  You can see that the speed of the heavier rider increases more quickly and reaches a larger final value.

Speed vs time for two cyclists (150lbs and 200lbs) heading downhill.  Because of air resistance, the 150lb rider accelerates more slowly and reaches a lower terminal velocity.

This final value is known as terminal velocity – maybe you’ve heard the term before.  An object reaches terminal velocity when the accelerations from gravity and drag exactly cancel.  Zero acceleration doesn’t mean zero motion – it just means that your speed no longer changes.  A heavier rider has a larger terminal velocity.   

Get rid of the air and what would happen?  Apollo 15 astronauts performed exactly this experiment on the moon, where there is no air.  A hammer and a feather fall at the same rate when there is no drag!  So if cycling races took place on the moon, the heavier riders would have no advantage on the downhills.  Now accepting registrations for the Tour de Moon.

Hands-on science for everyone

Over the last ten years, while working on my bachelor’s degree and now my PhD in physics, I have come to view the world through the lens of science.  I would not have ventured down this enlightening and exciting journey had the seeds of scientific curiosity not been planted early in my childhood.  I strongly believe the scientific method is the best tool we have for understanding the world that we occupy, and how to make it better for all of its inhabitants.  A well-educated society is critical for solving the great problems of our time.   Unfortunately, our country is struggling to create and promote scientific literacy.  Too often I hear that science and math are boring, or that “I’m just not a science person.”  I’m not advocating that everyone get a PhD in physics.  But I do believe everyone should be able to think like a scientist – question freely, challenge arguments from authority, and re-evaluate beliefs based on evidence.  Everyone should have a chance to build an experiment with their own hands, confront their assumptions, and come out on the other side having learned something and created something new. 

 

Thinking like a scientist doesn’t mean memorizing the atomic mass of germanium, reciting pi to 100 digits, or solving complex equations in your head.  Being a scientist doesn’t require pocket protectors or taped-together glasses.  Would you believe that I never even wear a white lab coat?  Sure, you’ll see all of these things in a lab, but that’s just because scientists are just as diverse as the rest of the world.  Anyone can be a scientist.  And everyone deserves the chance to discover through science. 

As a kid I loved creating things that would maybe considered more artsy than science-y.  I’ve since learned that science too can be an art.  Putting together an attractive presentation or poster can make all the difference in keeping your audience’s attention.  Making eye-catching computer animations can help explain what’s happening in my experiments – things that are usually too small to see or photograph.  Art and science are really inseparable.   

Growing up, I had so many opportunities to “create” at the intersection of art and science:  here you can see a diorama of the Mojave desert, an F-15 fighter jet made of K’NEX, and my attempt at an x-ray machine (this one lets you see all the organs, in color).

The Mojave Desert, an F-15, and my organs (not shown actual size)

Now the contraptions I create are a bit more complicated, sure.  But I still just feel like a kid in the lab, who gets to go play with a set of toys, trying to figure out what makes ‘em go.

Me with the microscope that I built.  It can "see" magnetism!

Let’s help more young kids get their hands dirty.  The first project I am highlighting on my donor page hits very close to home.  Not only is it right here in Columbus, OH, but the students will get to explore simple machines with K’NEX (which have a special place in my heart), and experiment with magnetism (something I do everyday in the lab!).  I love the hands on approach Ms. Sunnucks is taking with her students at Columbus Bilingual Academy. 

Introduction

Hello friends and family,

This September 7, I will be competing in a half-ironman distance triathlon at Cedar Point in Sandusky, OH.  While training for this event, I would like to raise money to support K-12 science education through DonorsChoose.org.  This website gives dedicated, active teachers a way to fund innovative and exciting projects to engage their students, for which they wouldn’t otherwise have the means.  People like you and me can pick which projects to donate to, and DonorsChoose.org buys and ships the supplies to the schools.  They’ll send you photos of the students taking part in the project and a letter from the teacher (that way you know your money was used responsibly).  For donations over $50, you can expect a hand-written thank you from the students themselves!

I’m calling this project “Sciathlon” – each week of training, I plan to share a story describing one small way science has changed the way I view the world.  By doing so, I hope to promote the value of science, and convince others that it is worth giving young students the ability to embark on their own scientific adventures. 

I have been fortunate enough to receive a fantastic education over my lifetime.  Not everyone is so lucky.  I would never have traveled down this “scientific” path without the opportunities I had as a kid – tinkering with K’NEX, debugging (or breaking) the family computer, and reading everything I could get my hands on about dinosaurs and airplanes.  With your help, I hope many young students get to experience the excitement and wonder of scientific discovery.

I will suggest several science projects on DonorsChoose.org which I find particularly creative, educational, and immersive.  I will post these here and on my donor page at http://www.donorschoose.org/sciathlon.  If you like these projects, please consider donating directly to them.  Alternatively, please peruse the website yourself, searching for interesting projects (science or otherwise) and feel free to donate to whatever you feel worthwhile.  Feel free to share with me any exciting projects that you stumble across, and I will re-blog them for others to check out.

Thanks for your support!