How To: Absurd Scientific Advice for Common Real-World Problems

by Randall Munroe

A falling person’s terminal velocity is around 130 miles per hour (mph).

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.

High-frequency sounds are absorbed by air as they travel through it, so they fade out quickly. That’s why nearby thunder makes a higher-pitched “cracking” sound, while faraway thunder makes a low rumble. They both sound the same at the source, but over a long distance, the high-frequency components of the thunder are muffled and only the low-frequency ones reach your ear.

while ultrasound travels less far than normal sound, infrasound travels farther. An infrasonic signal with a frequency below 1 cycle per second—1 Hz—can travel all the way around the planet.

real rivers don’t flow at a uniform speed. Water tends to go faster in the middle than at the edges, and faster near the surface than at the bottom. The fastest-moving parts are usually over the deepest parts of the river, a little under the surface.

In general, over the last half century, weather forecasts have been improving at a rate of 1 day per decade, which works out to about 1 second per hour.

Bolt’s agent told The New Yorker that Bolt has never run a mile.

The actual explanation for why ice is slippery is, surprisingly, still the subject of ongoing physics research.

In addition to ice skates, physicists don’t really understand what causes electric charges to build up in thunderstorms, why sand in an hourglass flows at the speed it does, or why your hair gets a static charge when you rub it with a balloon.

When a competitor’s score in a sport is strongly correlated with their odds of dying, it creates obvious problems for the sport.

In general, wind speeds increase the higher you go, so if you build a taller turbine, you can get more power from it.

A more comprehensive survey by Dr. Reuben J. Thomas, published in Sociological Perspectives, asked 1,000 US respondents for information about how they met their two closest friends. The study used the answers to build up a profile of how friendships form at different ages. Some sources of friendships remained relatively steady—at all ages, people made about 20 percent of their new friendships through family, mutual friends, religious organizations, or encounters in public settings. Other sources of friendships wax and wane throughout life—at first school dominates, followed by work. Then, as people approach retirement age, they become more likely to make friends around the neighborhood and at volunteer organizations.

How far away should you hold the phone? To minimize perspective distortion between several objects in a frame, the distance to the phone should be much larger than the difference in distance between the nearest and farthest objects.

When you zoom in, you change the apparent size of objects in the background. If you’re standing in front of a large object that’s far away, such as a mountain, the camera’s zoom can dramatically affect how big the mountain looks. If you set up your camera on a timer and walk far away from it, you can make even a fairly small mountain look huge.

Wood, like many materials, is stronger in tension than compression.

There’s no nondestructive test for indestructibility.