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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“Torque” isn’t just a terrible movie from 2004…

…it’s also an important concept that many of my physics students have studied recently.

Conceptually, torque is the quantity required to make an object rotate around a given point. I’m being very careful to avoid phrases like “how hard you have to turn something”, because there are ways to increase your torque without increasing the force you’re applying.

Distance from the point the object is rotating around is also a factor, as evidenced by the device I found in my parents’ kitchen.

Screen Shot 2016-02-07 at 11.13.07 PM
This photo is from Amazon, but I think my parents got theirs from the kitchen supplies equivalent of an Avon rep.

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Come for the cat video, stay for the science…

This showed up in my Facebook feed the other day.

As I watched this video about six or seven times in a row, you know I couldn’t help but consider the physics behind the poor kitty’s plight. We’ve discussed how an object only changes its motion (starts moving, stops moving, changes speed, changes direction) if an overall force acts on it. When a cat jumps off the floor, what’s applying the force that allows her to start moving upward?

Oddly enough, the floor is.

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Physics (not) by the numbers: work and energy

I tutor several physics students right now, and I find myself starting a lot of conversations with the phrase ‘let’s look at this conceptually for a second’. Don’t get me wrong, I love math, but sometimes we have to step away from the numbers and formulae and use our words.

Work and energy are good topics to tackle conceptually. Like many words, they have very specific meanings in physics that differ from the colloquial usage.

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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.)

There are at least two sides to every situation…

…but a Mobius strip is not a situation; it’s a one-sided object. Having trouble imagining it? Fire up your copy of Mario Kart 8 and play the first course in the Flower Cup…don’t have that? Come over and play it at my house, unemployment is LONELY. Or you can just try this at home.

You’ll need:

  • a narrow strip of paper at least 15 cm long (around 6 inches, if you insist on not using metric)
  • two different colored pens or pencils
  • scotch tape

Got all that? Here goes:

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