下载掌阅APP，畅读海量书库
立即打开
You’ve decided to throw a pool party. You’ve got everything—snacks, drinks, floating inflatable toys, towels, and those rings you throw into the pool and then have to dive in to retrieve. But the night before the party, you can’t shake the feeling that you’re missing something. Looking around your yard, you realize what it is.
You don’t have a pool.
Don’t panic. You can solve this problem. You just need a bunch of water and a container to put it in. Let’s figure out the container first.
There are two main types of pools: in-ground and above-ground .
An in-ground pool is, when it comes down to it, a fancy hole. This type of pool can take more work to install, but is also less likely to collapse in the middle of your party.
If you’d like to build an in-ground pool, first consult chapter 3: How to Dig a Hole. Use those instructions to dig a hole roughly 20 feet by 30 feet by 5 feet. Once you’ve created a hole of the appropriate size, you may want to line the walls with some kind of coating to keep the water from turning to mud or draining out before the party is over. If you have some giant plastic sheets or tarps lying around, you can use those, or you can try a spray-on rubber coating—there are ones designed for lining the beds of koi ponds. Just tell the salespeople you have some really large koi.
If you decide an in-ground pool isn’t the option for you, you can instead try an above-ground pool. The design of this type of pool is relatively simple:
Unfortunately, water is heavy—ask anyone who’s ever filled a fish tank on the floor and then tried to lift it up onto a table. Gravity pulls the water downward, but the ground pushes back equally hard. The water pressure is redirected outward, toward the walls of the pool, which are stretched in all directions. This tension, called hoop stress , is strongest at the base of the wall where the water pressure is the highest. If the hoop stress exceeds the tensile strength of the wall, the wall will burst. *
Let’s pick a possible material—say, aluminum foil. How deep can the water in an aluminum-foil-walled pool get before the sides burst? We can figure out the answer to this question, and lots of other pool design questions, using the formula for hoop stress:
Let’s plug in the numbers for aluminum foil. Aluminum has a tensile strength of around 300 megapascals (MPa), and sheets of foil are roughly 0.02 mm thick. Let’s assume our pool is 30 feet in diameter, so there’s plenty of room for games. We can plug those values into the hoop stress equation and rearrange things to figure out how deep the water in our shiny, crinkly pool can get before the hoop stress equals the tensile strength of the aluminum and the walls give out:
Sadly, 5 inches of water is probably not enough for a pool party.
If we swap out the thin aluminum foil for inch-thick pieces of wood, the math looks much better. Wood has a lower tensile strength than aluminum foil, but it makes up for it by being thicker, and could hold water 75 feet deep. If you happen to have a 30-foot-wide wooden cylinder with inch-thick walls lying around, that’s great news for you!
You can also rearrange the equation to tell you how thick the pool’s walls need to be to support a desired water depth. Let’s say we want our pool to be about 3 feet deep. Given the tensile strength of a material, this version of the formula tells us the minimum wall thickness necessary to hold the water:
The great thing about physics is that you can run these numbers for any material you want, even if it’s something ridiculous. Physics doesn’t care if your question is weird. It just gives you the answer, without judging. For example, according to the comprehensive 456-page handbook Cheese Rheology and Texture , hard Gruyere cheese has a tensile strength of 70 kPa. Let’s plug that into the formula!
Good news! You’ll only need a two-foot-thick wall of cheese to contain your pool! The bad news is that you may have trouble convincing anyone to jump in.
Given the practical problems associated with cheese, you should probably stick to traditional materials like plastic and fiberglass. Fiberglass has a tensile strength around 150 MPa, which means a wall just a millimeter thick would be strong enough to contain the water with extra tensile strength to spare.
Now that you’ve got your pool—whether in-ground or above-ground—you’ll need some water. But how much?
Standard backyard in-ground pools vary in size, but a medium-size one large enough to have a diving board might hold 20,000 gallons of water.
If you have a garden hose and a municipal water supply, then you could potentially fill your pool that way. But whether or not you can fill a pool quickly depends on the flow rate from your hose.
If you have good water pressure and a large-diameter hose, your flow rate might be 10 or 20 gallons per minute, which is enough to fill your pool within a day or so. If your flow rate is too low—or if you have well water, which may run out before you fill your pool—you might need to look for a different solution.
In many areas, online retailers like Amazon offer same-day delivery. A 24-pack of Fiji water bottles currently costs about $25. If you have $150,000 to spare—plus another $100,000 or so for same-day delivery—you can simply order a pool in bottle form. As a bonus, your new pool will consist entirely of water shipped from Fiji.
This will present a new challenge. When the water is delivered, you’ll need to get it all into the pool.
This will be trickier than you might have thought. Sure, you could unscrew the cap on each bottle and dump the water into the pool one by one, but this would take a few seconds per bottle. Since there are 150,000 bottles and only 86,400 seconds in a day, anything that takes more than a second per bottle is definitely not going to work.
You could try slicing the caps off an entire 24-pack of bottles with a sword. Many slow-motion videos online show people cutting through a row of water bottles with a sword. Judging from the videos, it’s surprisingly hard to do—the sword tends to be deflected up or down as it passes through the bottles. Even if you had a precise enough swing, along with the requisite arm strength and endurance, using a sword would probably be too slow.
Guns probably wouldn’t work too well, either. With careful planning and an efficient setup, you could use some kind of shotgun to make holes in a whole case of bottles at once, but you’d still have a hard time puncturing all the bottles and making them all fully drain fast enough to get through them all. You’d also end up with a pool full of lead, which—especially if you added chlorine to the water—would corrode and could eventually contaminate the groundwater.
There are a wide variety of increasingly powerful weapons you could use to try to open these bottles quickly; we won’t run through them all here. But before we leave weapons behind and move on to a more practical solution, let’s take a moment to consider the biggest and most impractical option of all. Could you open bottles using nuclear bombs?
This is a completely ridiculous suggestion, so it should come as no surprise that it was studied by the US government during the Cold War. Early in 1955, the Federal Civil Defense Administration bought beer, soda, and carbonated water from local stores, then tested nuclear weapons on them. *
Now, they weren’t trying to open the beverages. The purpose of the test was to see how well the containers survived, and whether the contents were contaminated. The civil defense planners figured that, after a nuclear explosion in a US city, potable water would likely be needed by first responders, and they wanted to know whether commercial beverages would be a safe source of hydration. *
The saga of the government’s nuclear war on beer is cataloged in a 17-page report titled The Effect of Nuclear Explosions on Commercially Packaged Beverages , a copy of which was helpfully unearthed by nuclear historian Alex Wellerstein.
The report describes how the bottles and cans were placed in various locations around the Nevada test site for each explosion. Some were in refrigerators, some on shelves, and some just sitting on the ground. * They carried out the experiment twice, during two different nuclear tests conducted as part of Operation Teapot.
The beverages fared surprisingly well. Most of them survived the blast intact. Those that didn’t were mostly punctured by flying debris or exploded when knocked off the shelves. They also had low levels of radioactive contamination, and even tasted ok.
Post-explosion beer samples were sent for “carefully controlled testing” at “five qualified laboratories.” * The consensus was that the beer mostly tasted fine. They concluded that beer recovered after a nuclear blast could be considered a safe source of emergency hydration, but that it should probably be tested more carefully before it was put back on the market.
Plastic bottles weren’t common in the 1950s, so all the tests used glass and metal bottles. However, the tests still suggest that nuclear weapons probably don’t make great bottle openers.
Luckily for us, there’s a type of device which can accomplish our goal much more quickly than a sword, shotgun, or nuclear weapon: an industrial plastic shredder. Shredders are used by recycling centers to shred large volumes of plastic bottles, and—as a bonus—they can strain out the liquid for you.
A shredder like the Brentwood AZ15WL 15kW can handle a throughput of 30 tons per hour—including both plastic and liquid, according to Brentwood marketing materials. This would let you fill your pool in a little over 2 hours.
Industrial shredders come with price tags in the five to six figures, which is a lot for one party (although it’s nothing compared to what you already spent on water bottles.) But maybe, if you mention how many nuclear weapons you have, you can convince them to give you a discount.
If someone else has a pool nearby, and they’re at a slightly higher elevation, you can steal the water using a siphon. If you can connect the two pools with a tube of water, you can get water to flow steadily from their pool into yours.
Note : Siphons can lift water up out of a pool and over small barriers like fences, but if the middle of the siphon goes more than 30 feet above the surface of your neighbor’s pool, water won’t flow. Siphons are driven by atmospheric pressure, and Earth’s air pressure is only capable of pushing water up 30 feet against gravity.
Water is made up of hydrogen and oxygen. There’s plenty of oxygen in the atmosphere, * and while hydrogen is certainly rarer, it’s still not too hard to find.
The good news is that if you get a bunch of hydrogen and oxygen together, it’s easy to turn it into water. You just apply a little bit of heat, and the chemical reaction keeps going. In fact, it’s pretty hard to stop.
The bad news is that sometimes the chemical reaction gets started by accident. We used to have big hydrogen-filled airships flying around, but after some dramatic incidents in the 1930s, we started filling them with helium instead. Nowadays, if you want hydrogen, the best place to get it is by collecting and reprocessing the byproduct of fossil fuel extraction.
You don’t need to combine hydrogen and oxygen to create water when there’s already-created H 2 O floating around in the air in the form of water vapor—the stuff that condenses to form clouds and sometimes even falls in the form of rain. On average, each square meter of the Earth has about 6 gallons of water in the column of air above it, the equivalent of a couple of 24-packs of water bottles. *
If all that water fell as rain, it would form a layer about an inch thick. If your property is 1 acre in size, and the air has an average amount of moisture, then there are about 25,000 gallons of water in the air overhead. That’s enough to fill a pool! Unfortunately, a lot of that water is pretty high up and hard to get to. It would be nice if we could make the water fall on cue, but despite periodic attempted cloud-seeding projects, no one has found a way to reliably induce rainfall.
The usual way of extracting water from air is to make the air flow past a cold surface, so the water condenses out of it as dew. To get all the water out of your air, you’d need to build a several-mile-high cooling tower. Luckily for you, air moves around on its own, so you don’t need to build a mile-high tower—if there’s a breeze, you can just collect the moisture from the air as it flows past your house.
Moisture collection is really a pretty inefficient way to gather water. It takes a lot of power to cool and condense water out of the air. In most cases, you’d use a lot less energy by just driving a truck to an area with more water, filling it up, and driving back. Besides, even under ideal conditions, this kind of humidifier is unlikely to produce enough water to fill your pool any time soon, and it might annoy your neighbors who live downwind of you.
There’s a lot of water in the sea, * so probably no one will mind if you borrow a little. If your pool is below sea level, and you don’t mind a saltwater pool, this might be an option. All you need to do is dig a channel and let the sea flow in.
This has actually happened in real life, by accident, very dramatically.
Malaysia was once the world’s largest producer of tin. One of the mines that produced this tin was constructed near the western coast, just a few hundred feet from the ocean. After the tin market collapsed in the 1980s, the mine was abandoned. On October 21, 1993, the water broke through the narrow barrier separating the mine from the sea. The ocean rushed in, filling the mine in a matter of minutes. The lagoon created by the flood remains to this day, and can be seen on maps at 4.40°N, 100.59°E. The cataclysm was recorded by a bystander with a camcorder, and the footage has since been uploaded to the internet. Despite its low quality, it’s one of the most jaw-dropping pieces of video ever recorded. *
If the bottom of your pool is above sea level, connecting it to the ocean won’t work; water would just flow downhill to the sea. But what if you could bring the sea up to you ?
Well, you’re in luck; it’s happening whether you want it to or not. Thanks to the trapped heat caused by greenhouse gases, the seas have been rising for many decades now. Sea-level-rise is caused by a combination of melting ice and thermal expansion of the water. If you want to fill your pool, you could try accelerating sea-level rise. Sure, it would worsen the immeasurable ecological and human toll of climate change, but on the other hand, you could have a sweet pool party.
If you wanted to cause rapid sea-level-rise, and you happened to have a giant ice sheet on the land next to your house, you might think that melting it would be a great way to raise the sea level.
But, because of some counterintuitive physics, melting an ice sheet next to your house might actually lower the sea level. What you want to do is melt ice on the other side of the world .
The reason for this bizarre effect is gravity. Ice is heavy, and when it’s sitting on land, it pulls the ocean slightly toward it. When it melts, the water level goes up on average, but since it’s no longer being pulled as hard toward the land, it can actually go down in the area around the ice that melted.
When ice from the Antarctic ice cap melts, sea level goes up the most in the northern hemisphere. When ice in Greenland melts, on the other hand, it raises sea levels most around Australia and New Zealand. If you want to raise sea level near where you live, check whether there’s an ice sheet on the other side of the planet. If so, that’s the one you should melt.
If there are no convenient ice caps to melt—or you don’t want to contribute to global sea-level-rise—you could try to do what farmers have been doing to get water for thousands of years: borrow a river.
You could find a nearby river and encourage it—via a temporary dam—to flow toward your pool long enough to fill it up. But be careful: this kind of project has gone wrong before.
In 1905, engineers on the California/Arizona border were digging irrigation canals to bring water to farms from the Colorado River. The mission to divert water from the Colorado River was, unfortunately, too successful. The water flowing into the new canal started eroding a deeper and wider path, which let more water flow in. Before they could pull the plug, * the river had been captured completely. It inundated a formerly dry valley downstream from the irrigation project, filling it and creating a new—completely accidental—inland sea.
The Salton Sea, which has waxed and waned over the last century, is currently drying up as more water is diverted for irrigation. The windblown dust from the dry lake bed, contaminated with agricultural runoff and other pollutants, blows through nearby towns, sometimes making it hard to breathe. The contaminated, increasingly salty water has led to massive die-offs of aquatic life, and the decaying algae and dead fish have created an omnipresent rotten-egg smell which occasionally wafts west as far as Los Angeles.
That might sound bad, but don’t worry—those disastrous environmental consequences took a while to develop.
In fact, the Salton Sea was briefly popular as a resort destination, with yacht clubs, fancy hotels, and swimming. Later, as conditions in the sea deteriorated, the resorts all turned to ghost towns. But you can worry about all those consequences tomorrow.
For now, it’s pool party time!
