Love is a “shocking” sensation

In honor of the SigFig’s birthday, today’s post is about the moment I knew we really had something special.

It is, unsurprisingly, science-related.

Several years ago, we were walking along the waterfront and paused to rest on a high-backed plastic bench. I kissed him and felt a mild shock.

“You’re crackly. Discharge.”

Without missing a beat, he got up and touched his fingertip to a metal railing. He knew exactly what I meant and exactly what he had to do to rectify the situation.

And, just like that, I was hooked.

So what was going on here? It’s all about the electrons.

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…If there were only three bulbs wired in parallel, could I refer to it as a three-ring circuit?

For whatever reason, there are nine light bulbs installed in our living room ceiling (three recessed, controlled by two different switches, and six on a zigzag-shaped fixture, controlled by a single switch). I clearly think this is an excessive number, as evidenced by the fact that, a few weeks ago, I was working away happily in what I felt was a perfectly adequately lit room. The SigFig then walked in, looked up, and pointed out that most of the bulbs in the fixture had burned out. A single light bulb soldiered on amongst its burned-out brethren.

I did what any scientifically-minded person would: I started thinking about circuits.

Anything that runs on electricity contains some form of circuit. Simple circuits consist of electrical energy sources (such as batteries or home electric grids), resistors that transform that electrical energy into other forms of energy (such as heat and light), and wires to connect these elements. Circuit diagrams show how the parts of the circuit are put together.

BasicCircuit

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Up, down, on top, on bottom, strangely…

…and with charm.

You’ve probably noticed that I like puns; when I spent a lovely Saturday afternoon participating in a charm bracelet walk with a couple of friends in nearby Snohomish, a certain quark pun of questionable propriety ran through my mind. However, what really got my science-gears turning was the sight of skydivers as they descended into the nearby fields.

Air resistance is a topic I’ve tackled on many different occasions, including a post on this very blog. (If you haven’t tried the activity described at the end of the post, go for it now!) Parachutes work because air, being a fluid, exerts a force on objects that move through it. As the surface area of an object increases, the air has more space to push on it, thus increasing the total force exerted on the object. A parachute has a large surface area and a relatively low mass, meaning that the large upwards force due to air resistance is only minimally canceled out by a smaller downward force due to gravity. After a quick review of freebody diagrams, we can see that the net force on the parachuted skydiver is actually upwards, yet he continues to move downwards.

This counterintuitive detail trips up many students. What we have to remember from Newton’s Second Law (Force=mass*acceleration) is that our net force shows the us the direction of our acceleration, not our motion. Let’s define the downward direction to be positive. An upward net force indicates a negative acceleration; since acceleration is a measure of how quickly an object’s velocity is changing, and our skydiver is not changing direction, a negative acceleration represents a reduction in speed. Our analysis of the forces shows us that the skydiver is slowing down, and that’s exactly what we see.

You can experience this phenomenon even if you have a fear of heights. Like air, water is a fluid and exerts a force analogous to air resistance. Tape rocks or small weights along one edge of a clean trash bag. Take it to a pool (preferably one owned by friends of yours) that is about five feet deep (four, if, like me, you are a shade under five feet tall). Start running through the pool, then spread your arms out and hold the trash bag behind you, weighted end down, like a cape. The water will exert a force on the trash bag and you’ll slow down.

(This should go without saying, but PLEASE don’t try this unless you have permission.)

…don’t worry, it’s perfectly normal.

AKA Freebody Diagrams, Part Two.

For a definition of/conceptual take on freebody diagrams and the forces within them, make sure you check out Part One, then head on back here to plug in the numbers.

Let’s begin by reviewing our basic freebody diagram from last time- but with one small change.

standardfreebodydiagramlessfriction
Click to enlarge.

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If you’re feeling a little perpendicular tonight…

…or, Freebody Diagrams: Part One.

How does a 27-year-old science enthusiast amuse herself on a Saturday night? By doing things like this:

OLYMPUS DIGITAL CAMERA
Tiny Einstein is always watching.

So what on Earth is this? (Besides evidence that I’ve really got to get out more…) This is an elaborate photographic representation of a freebody diagram, which is a visual tool that you can use to analyze the forces acting on an object. In a freebody diagram, you draw arrows to represent the strength and direction of all the forces acting on an object. The standard introductory freebody diagram has four forces in it:

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