2018-01-23T17:27:23.790Z
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## Electrofishing for Whales

Electrofishing for Whales

I used to work on a fisheries crew where we would use an electro-fisher backpack to momentarily stun small fish (30 - 100 mm length) so we could scoop them up with nets to identify and measure them. The larger fish tended to be stunned for slightly longer because of their larger surface area but I don't imagine this relationship would be maintained for very large animals. Could you electrofish for a blue whale? At what voltage would you have have to set the e-fisher?

So you want to give endangered whales powerful electric shocks. Great! I'm happy to help. This is definitely a very normal thing to want to do.

There are various electrofishing setups, but they all operate on the same general principle: An electric current flows through the water, and also through any fish that happen to be in the water. The electric current, through a few different physical effects, draws the fish toward one of the electrodes and/or stuns them.

For a long time, people didn't really notice that electrofishing injured fish at all. For the most part, stunned fish seemed to be fine after a few minutes. However, they frequently suffer from internal damage which isn't obvious from the outside. The electric current causes involuntary muscle spasms, which can fracture the fish's...

## Toaster vs. Freezer

Toaster vs. Freezer

Would a toaster still work in a freezer?

My Brother, My Brother and Me, Episode 343, discussing a Yahoo Answers question

On a recent episode of Justin, Travis, and Griffin McElroy's terrific advice podcast, My Brother, My Brother and Me, the brothers pondered a Yahoo Answers question about what would happen if you put a toaster inside a freezer. (The discussion comes around the 36-minute mark.)

They have a fun discussion of a few aspects of the problem before eventually moving on to the next question. Since they don't really settle on a final answer, I thought we could help them out by taking a closer look at the physics of freezer toasters.

(A quick safety note: If you actually do this, keep in mind that the toaster may melt some of the ice in the freezer, leaving you with a running electrical appliance in a pool of water.)

Griffin sums up the situation like this:

You put a toaster in a freezer. You run the extension cord in there. You put some good bread in there. You click it down. What even happens, right? Because if your answer is, "it would get hot," then the freezer hasn't done its job. But if you say "it would get cold," then the toaster hasn't done its job.

For starters, the answer: The toaster would win. The freezer wouldn't do its job. Toasters beat freezers.

## Coast-to-Coast Coasting

Coast-to-Coast Coasting

What if the entire continental US was on a decreasing slope from West to East. How steep would the slope have to be to sustain the momentum needed to ride a bicycle the entire distance without pedaling?

—Brandon Rooks

Too steep to actually build, sadly. But for the next best thing, I suggest a vacation to the Hawaiian island of Maui.

First, the physics. Bikes coast downhill. On a long enough slope, a bike will reach a certain steady coasting speed. On a steep hill, their coasting speed will be faster, and on a gentle slope, they coast more slowly. If the slope is small enough, the bike will slow down and stop.

The shallowest slope at which a bike will still roll steadily forward is determined by the bike's coefficient of rolling resistance. In fact, the formula for this minimum slope—measured in terms of vertical drop over horizontal distance—is incredibly simple:

$\text{Minimum slope} = \text{Coefficient of rolling resistance}$

"Slope equals coefficient of friction"[1]Sliding friction and rolling resistance work in different ways, but the coefficients are equivalent in these types of problems. If you want to be precise, you could use the phrase "coefficient of resistance" for all of them, but "coefficient of friction" is the more common term. is a handy general rule...

## Hide the Atmosphere

Hide the Atmosphere

Earth’s atmosphere is really thin compared to the radius of the Earth. How big a hole do I need to dig before people suffocate?

—Sam Burke

The idea here is straightforward: When you dig a hole in the ground, the hole fills up with air.[1]The dirt you pile up outside the hole displaces air, so at first you won't have much effect on the surrounding atmosphere, but the effect grows as the hole gets deeper and the pile gets higher. So keep at it! If you dig a big enough hole, most of the atmosphere will flow in, and there won't be enough left outside the hole to breathe.[2]You need to remove about 65% of the atmosphere before sea level air becomes too thin to support human life.[3]As this paper points out, it's odd—and likely coincidental—that the highest point on Earth happens to be just about exactly as high as the human high-altitude survival limit.

The atmosphere's exact volume is tricky to define, since it gets thinner at higher altitudes and doesn't have a firm boundary. If you compressed the whole thing to the density of normal surface air, it would be about 10 kilometers thick, and take up a volume of 4 billion cubic kilometers. 4 billion km3 of air is enough to fill a cube...

## Flood Death Valley

Flood Death Valley

Since Death Valley is below sea level could we dig a hole to the ocean and fill it up with water?

—Nick Traeden

Yes! We can do anything we want. We shouldn't do this, though, because it would be gross.

Death Valley is an endorheic basin[1]"Big hole" in California. The floor of the valley is about 80 meters below sea level. It contains the lowest point on land in North America[2]Excluding artificial points like mines. and is the hottest place on Earth.[3]If you're about to say "Wait, what about Liby—," then don't worry, I'm with you. Just hang on and read a few more words ahead!

Now, if you're the sort of person who's into world records, you might have heard that the hottest place on Earth was Al Azizia, Libya. Al Azizia recorded a temperature of 58.0°C (136.4°F) in 1922, a mark Death Valley has never come close to. So what gives?

It turns out Al Azizia has recently been stripped of its record. In 2010, an exhaustive—and definitely a little obsessive—investigation led by Christopher C. Burt convinced the World Meteorological Organization that the Libyan measurement was probably a mistake. This left Death Valley with...