That beeping noise is the sound of “cold escaping”

Today’s title brought to you by my refrigerator, which beeps if you leave the door open for too long. I imagine it’s the light bulb letting you know that it’s tired of being on.

This modern marvel automates the scolding our parents always gave us when we spent too long contemplating the apple-juice-vs.-orange-juice decision: “Close the fridge, you’re letting the cold out.” Which is an environmentally friendly, if not altogether scientifically accurate, chastisement. It would be more accurate to say that you’re letting the heat in.

While cold air can flow out of a fridge when you open the door, a chilled milk carton sitting on the shelf doesn’t emanate “cold.” If you propped the door open, the carton would warm up. But it wouldn’t warm up because it released all the “cold” it was holding onto, it would warm up because it absorbed energy from the warm air around it.

Temperature is a measure of the average kinetic (motion-related) energy of the particles in a substance. The faster the particles in a substance are moving, the higher the temperature of the substance. So if the temperature of a substance rises, it means that the substance’s particles sped up. In order to move faster, the particles had to absorb energy from somewhere else. When you leave the refrigerator door open, the warm air particles will transfer energy to the cold particles in the milk carton. This energy transfer is what we call heat. Heat always flows from warmer substances to cooler substances. In the case of the milk carton, heat will flow from the warm air to the cold milk carton, cooling down the air and warming up the carton, until the two have reached the same temperature. Yay thermal equilibrium!

It’s heat flow that causes objects to feel hot or cold. Your body isn’t a thermometer; you don’t feel absolute temperature. Something feels hot if heat flows into your hand when you touch it, and something feels cold if heat flows out of your hand when you touch it.

Take three cups of water: one cold, one hot (but not too hot! hot water straight from the tap is fine!), and one room temperature. Put your left hand in the cold water and your right hand in the hot water. Leave them there for 20-30 seconds, then place both of your hands in the room temperature water. If your hands felt absolute temperature, they should feel the same when you put them in the room temperature water. They won’t. Is heat flowing into or out of your right hand? What about your left hand? How does the direction of heat flow explain what’s going on?


The one with the lesser “mew”

Yes, I’m late, but I’d be remiss in my nerdly duties if I ignored Pi Day (also Einstein’s birthday!) completely.

I was introduced to the concept of pi when I was just a wee little geeklet, and I remember thinking that the joke “pie are not round, pi r squared!” was absolutely the funniest thing ever. My sense of humor hasn’t changed all that much; now my favorite joke is the one about two cats of the same mass and which one will be the first to slide off of a slanted tin roof.

But in a belated celebration of pi day, I should talk about something circular now.

What distance does a wheel travel when it makes one full rotation? This is something that I have talked about both in my former job as a physics teacher and in my current job as a math tutor. Many students will correctly intuit that the distance traveled is equal to the circumference of the wheel. But how can we make the idea concrete?

With toilet paper, of course. If you want to see the distance that a wheel covers as it rolls, you need something that leaves a trail. I would take a roll of toilet paper, point the tube toward me, and draw a line down the side of the roll. Then I’d put the roll on the table with the tube pointing toward the class and the ink mark pointing straight down to the table. I’d unroll the roll until the mark was pointing straight down to the table again, showing that the roll had completed one full rotation. How far did it go? The length of the toilet paper that was unrolled = the distance between the ink marks = the amount of paper needed to wrap around the roll once = the circumference. This solidified the idea for students, plus the toilet paper gave them enough tissue to blow their noses on for weeks.

So next time you see your cat unrolling your toilet paper, don’t chastise him. He’s just exploring rotational motion.

Note: ScienceInSuburbia is not responsible if you end up annoying your downstairs neighbors.

I’m definitely adjusting to and enjoying life in the suburbs, but I will always miss Boston’s public transportation system. Living in the suburbs without a driver’s license means two things:

1) I don’t go as many places as I used to.

2) I have to walk a lot farther to get to the places I do go to, whether it’s to get to a bus stop or to get to the location itself.

One of this week’s journeys took me across a pedestrian overpass high above a major freeway. Though I recognized the safety hazards of doing so, part of me definitely wanted to grab the nearest objects I could lift and go all-out Galileo. Yes, I know objects fall at the same rate (when air resistance is absent or negligible), but I want to see it for myself. Particularly from atop a pedestrian overpass high above a major freeway.

I frequently think about falling objects, partially because I used to be a physics teacher and partially because I am a clumsy person who drops things a lot. It’s hard to get students to really believe that objects fall at the same rate. Their direct observations tell them otherwise; after all, they know that, if their teacher drops a piece of paper and a textbook at the same time, the textbook will hit the ground first.

But that’s just because of air resistance. A piece of notebook paper and a textbook have roughly the same amount of air pushing up on them as they fall, but this force has a greater effect on the less massive paper. If we could just eliminate the air pushing up on the paper, we’d see that the two objects fall at the same rate. So how can we stop air from pushing up on the underside of the paper?

When I tackled this topic as a teacher, this was the point when I would put the piece of paper on top of the textbook and ask my students to predict what would happen when I dropped the two items together. Most said that the piece of paper would fly off the textbook and slowly flutter back down to the ground.

That isn’t what the paper does, but you don’t have to take my word for it.

In the name of science, get a piece of paper and a book and give it a go.

Rain, Rain, Go Away…

…no, seriously, just stop already.

The particular suburb I live in happens to be a suburb of Seattle. It probably doesn’t rain here as much as you think it does, but it still rains a lot. In fact, it’s raining right now and it’s supposed to rain all week.

Which brings me to the water cycle.

Anyone who has ever taught science or worked on science textbooks- myself included- has probably had his/her fill of the water cycle. You’ve probably seen the basic diagram yourself. (My current favorite rendition is from the US Geological Survey.) Water evaporates from oceans and lakes, condenses into clouds, rains/snows back down to Earth, eventually ends up back in those bodies of water, and the whole process starts over again. Plants also contribute to the water cycle by absorbing groundwater and releasing water into the air- you can see this process on a small scale by building a terrarium.

The water cycle is an excellent example of how incredibly easy it is to interrupt a natural process. Suppose I went outside and collected about an ounce of rainwater. I could put that rainwater in an airtight jar and stick it in the back of my fridge, effectively removing a whole lot of water molecules from the water cycle. (A figurative gold star to anyone who can tell me how many! A literal gold star to anyone who can both tell me how many and meet up with me in person.) Those molecules had moved through the water cycle for billions of years, and with one action I can relegate them to a spot between the Sriracha and the salad dressing.

Of course, this wouldn’t do a thing about how much rain Seattle gets this week.