YouTube // Physics Girl
YouTube // Physics Girl

Can You Solve the Boat Puzzle?

YouTube // Physics Girl
YouTube // Physics Girl

Ah, logic puzzles. Sometimes they seem so simple. Generally those are the times I get the answer wrong.

In this puzzle video, YouTube's Dianna Cowern (aka Physics Girl) poses a thought experiment: You're in a boat floating in a lake, holding a rock. You toss the rock out of the boat, into the water. What happens to the water level? Does the water level rise, fall, or stay the same?

As I mentioned above, this is one where I was extremely confident (and incorrect) in my answer. What's great about Cowern's answer is that she walks us through a methodology to figure out these kinds of problems, then gives us more puzzles to try. Learn up:

Note: This is one of those rare cases where the YouTube comments contain several substantive discussions (though they're still YouTube comments, so...beware).

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iStock
13 Scientific Explanations for Everyday Life
iStock
iStock

Science holds our lives together. It explains everything from why bread rises to why you need gas to power your car. In his book Atoms Under the Floorboards, author Chris Woodford lays out the abstract science that underlies the everyday world, from the big (how do skyscrapers stay up?) to the small (why does my laptop get hot when I’m watching Netflix?). Along the way, he also calculates the answers to whimsical questions like, “How many people would I have to gather together to keep my house warm without heat?” (A lot, but not as many as you'd think.) Here are 13 things we learned about the world through his eyes.

1. A POWER DRILL COULD SET YOUR HOUSE ON FIRE, IN THEORY.

Because of friction, electric drills generate heat. The motor, the drill bit, and the wall all get hot. It takes about 2000 joules of energy to heat one kilogram of wood just 1°C. Assuming a typical power drill uses 750 watts of electricity, and it puts out 750 joules of energy, Woodford calculates that it would take just four minutes to set fire to a wooden wall in a 68°F room.

2. STICKY NOTES COME OFF EASILY BECAUSE THEIR ADHESIVE IS UNEVEN.

Post-it Notes feature a plastic adhesive that is spread out in blobs across the paper. When you slap a Post-it onto your bulletin board, only some of these blobs (technically called micro-capsules) touch the surface to keep the note stuck there. Thus, you can unstick it, and when you go to attach it to something else, the unused blobs of glue can take over the adhesive role. Eventually, all the capsules of glue will get used up or clogged with dirt, and the sticky note won't stick anymore.

3. GUM IS CHEWY BECAUSE IT'S MADE OF RUBBER.

Early gums got their elastic texture from chicle, a natural type of latex rubber. Now, your bubble gum is made with synthetic rubbers like styrene butadiene (also used in car tires) or polyvinyl acetate (also used in Elmer’s glue) to mimic the effect of chicle.

4. OFFICE BUILDINGS ARE EVER-SO-SLIGHTLY TALLER AT NIGHT.

After all the employees go home, tall office buildings get just a little taller. A 1300-foot-tall skyscraper shrinks about 1.5 millimeters under the weight of 50,000 occupants (assuming they weigh about the human average).

5. A LEGO BRICK CAN SUPPORT 770 POUNDS OF FORCE.

LEGOs can support four to five times the weight of a human without collapsing. They are strong enough to support a tower 375,000 bricks tall, or around 2.2 miles high.

6. POLISHING SHOES IS LIKE FILLING IN A ROAD'S POTHOLES.

Regular leather appears dull to the eye because it’s covered in teeny-tiny scrapes and scratches that scatter whatever light hits the material. When you polish a leather shoe, you coat it in a fine layer of wax, filling in those crevices much like a road crew smoothes out a street by filling in its potholes. Because the surface is more uniform, rays of light bounce back toward your eye more evenly, making it look shiny.

7. YOU COULD HEAT YOUR HOUSE WITH JUST 70 PEOPLE.

People give off body heat, as anyone who has been trapped in a small crowded room knows. So how many people would it take to warm up your home with just body heat in the winter? About 70 people in motion, or 140 people still, figuring that humans radiate 100-200 watts of heat normally and that the house uses four electric storage heaters.

8. DENSITY EXPLAINS WHY COLD WATER FEELS COLDER THAN AIR AT THE SAME TEMPERATURE.

Because water is denser than air, your body loses heat 25 times more quickly while in water than it would in air at the same temperature. Water's density gives it a high specific heat capacity, meaning it takes a lot of heat to raise its temperature even a little, and it's very good at retaining heat or cold (the reason why hot soup stays hot for a long time, and why the ocean is much cooler than land). Water is a great conductor, so it's very effective at transferring that heat or cold to your body.

9. WATER CLEANS WELL BECAUSE IT HAS ASYMMETRICAL MOLECULES.

Because water molecules are triangular—made of two hydrogen atoms stuck to one oxygen atom—they have slightly different charges on their different sides, kind of like a magnet. The hydrogen end of the molecule is slightly positive, and the oxygen side is slightly negative. This makes water excellent at sticking to other molecules. When you wash away dirt, the water molecules stick to the dirt and pull it away from whatever surface it was on. This is also the reason water has surface tension: it’s great at sticking to itself.

10. THE "PULSE" SETTING ON A BLENDER WORKS BETTER BECAUSE OF TURBULENCE.

When your blender stops chopping up food and begins just spinning it around in circles, it’s because everything inside is spinning at the same rate. Instead of actually blending ingredients together, it’s experiencing laminar flow—all the layers of liquid are moving in the same direction with constant motion. The pulse function on the blender introduces turbulence, so instead of the fruit chunks rolling around the side of the blender, they fall into the center and get blended up into a smoothie.

11. BABIES' BODIES CONTAIN MORE WATER THAN ADULTS.'

Adults are around 60 percent water. By contrast, newborn babies are about 80 percent water. But that percentage quickly drops: A year after birth, kids' water content is down to around 65 percent, according to the USGS.

12. GLASS BREAKS EASILY BECAUSE ITS ATOMS ARE LOOSELY ARRANGED.

Unlike other solid materials, like metals, glass is made up of amorphous, loosely packed atoms arranged randomly. They can’t absorb or dissipate energy from something like a bullet. The atoms can’t rearrange themselves quickly to retain the glass’s structure, so it collapses, shattering fragments everywhere.

13. CALORIE COUNTS ARE CALCULATED BY INCINERATING FOOD.

Calorie values on nutritional labels estimate the energy contained in the food within the package. To figure out how much energy is in a specific food, scientists use a calorimeter. One type of calorimeter essentially burns up the food inside a device surrounded by water. By measuring how much the temperature of the water changes in the process, scientists can determine how much energy was contained in the food.

This story originally ran in 2015.

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Oli Scarff, Getty Images
How a Particle Accelerator Is Helping to Unearth Long-Lost Pieces of Art
Oli Scarff, Getty Images
Oli Scarff, Getty Images

A particle accelerator is revealing the people in 150-year-old photographs whose features had been lost to time, Science News reports.

For the first time, Madalena Kozachuk, a Ph.D. candidate at Canada’s Western University, and a team of scientists used an accelerator called a synchrotron to scan daguerreotypes, an ancestor of modern photography.

before and after image of a damaged dagguereotype
Kozachuk et al. in Scientific Reports, 2018

Invented by French painter and physicist Louis Daguerre, daguerreotypes were popular from around the 1840s to the 1860s. They were created by exposing an iodized silver-coated copper plate to a camera (the iodine helped make the plate's surface light-sensitive). Subjects had to sit in front of the camera for 20 to 30 minutes to set the portrait, down from the eight hours it took before Daguerre perfected his method. Photographers could then develop and fix the image with a combination of mercury and table salt.

Because they’re made of metal, though, daguerreotypes are prone to tarnish. Scientists can sometimes recover historical daguerreotypes by analyzing samples taken from their surface, but such attempts are often both destructive and futile, Kozachuk wrote in a study published in Scientific Reports.

Kozachuk found that using a particle accelerator is a less invasive and more accurate method. While some scientists have used X-ray imaging machines to digitally scan other historical objects, such instruments are too large to scan daguerreotypes. Reading the subtle variations on a daguerreotype surface requires a micron-level beam that only a particle accelerator can currently produce. By tracing the pattern of mercury deposits in the tarnished plate, the researchers were able to reveal the obscured image and create a digital photo of what the daguerrotype looked like when it was first made.

before and after image of a recovered dagguereotype
Kozachuk et al. in Scientific Reports, 2018

“When the image became apparent, it was jaw-dropping,” Kozachuk told Science News. “I squealed when the first face popped up.”

Scanning one square centimeter of each 8-by-7 centimeter plate took about eight hours. The technique, though time-intensive, may allow museums and collectors to restore old daguerreotypes with minimal damage.

“The ability to recover lost images will enable museums to expand their understanding of daguerreotype collections, as severely degraded plates would not otherwise have been able to be studied or viewed by interested scholars,” Kozachuk wrote.

[h/t Science News]

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