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Why Do Things Float in Water?

WHY? is our attempt to answer all the questions every little kid asksHave a question? Send it to why@mentalfloss.com.

I bet you know that wood floats but a rock sinks. But why? Let’s look deep inside each object at its molecules (MOLL-uh-kyools). Everything is made of molecules. Molecules are very, very tiny. You can only see them with a special microscope. In some objects, like a rock, molecules are squished tightly together. In others, like wood, the molecules are more spread out. How closely molecules are crowded together in a space is called density. Density is a big part of why some things float and others don’t.

Objects like coins, rocks, and marbles are more dense than water. They will sink. Objects like apples, wood, and sponges are less dense than water. They will float. Many hollow things like empty bottles, balls, and balloons will also float. That’s because air is less dense than water. This is one reason huge ships can float, even though they’re very heavy. Inside a ship, there’s a lot of hollow space filled only with air. But that’s not all: shape matters, too!

The outside of an object is called its surface. When more of the surface is touching the water, the object is more buoyant (BOY-ant), which means it floats better. When an object floats, it pushes water out of the way. That’s called displacement. But guess what? Water pushes back! So the more surface area an object has, the more water pushes back against it, helping it float. That's another reason why even big ships don't sink if they have the right shape.

You can test this out yourself. Try making a boat with a flat bottom using tinfoil. Does it float? What happens if you start putting pennies or pebbles inside your boat? What happens if you crumple your tinfoil boat into a ball? Using what you’ve learned about density and buoyancy, why do you think the empty boat floats best?

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15 Scientific Reasons Spring Is the Most Delightful Season
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Summer, winter, and fall may have their fans, but spring is clearly the most lovable of the four seasons. Not convinced? Here are 15 scientific reasons why spring is great:

1. TEMPERATURES ARE MODERATE.

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Spring marks the end of blistering winter and the transitional period to scorching summer. In many places, the season brings mild temperatures in the 60s and 70s. People tend to be most comfortable at temperatures of about 72°F, research shows, so the arrival of spring means you can finally ditch the heavy winter layers and still be comfortable.

2. THERE IS MORE DAYLIGHT.

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Following the spring equinox, days begin lasting longer and nights get shorter. Daylight Saving Time, which moves the clock forward starting in March, gives you even more light hours to get things done. Those extra hours of sun can be a major mood-booster, according to some research. A 2016 study of students in counseling at Brigham Young University found that the longer the sun was up during the day, the less mental distress people experienced.

3. THE BIRDS RETURN.

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Many animals migrate south during the winter, then head north as temperatures rise. For relatively northern regions, there is no better indicator of spring than birds chirping outside your window. Their northward migration can start as early as mid-February and last into June, meaning that throughout the spring, you can expect to see a major avian influx. In addition to the satisfaction of marking species off your bird-watching checklist, seeing more of our feathered friends can make you happy. In 2017, a UK study found that the more birds people could see in their neighborhoods, the better their mental health.

4. THERE ARE BABY ANIMALS EVERYWHERE.

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Many animals reproduce in the spring, when temperatures are warmer and food is plentiful. Baby bunnies, ducklings, chipmunks, and other adorable animals abound come spring. Studies have found that seeing cute animals can have positive effects on humans. For instance, one small study in 2012 found that when college students looked at cute images of baby animals, they were better at focusing on a task in the lab. Being able to watch fluffy baby squirrels frolic outside your office window might make spring your most productive season of the year.

5. YOU'RE SAFER.

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In 2015, a pair of public policy researchers discovered a hidden upside to "springing forward" for Daylight Saving Time. It reduced crime. When the sun set later in the evening, the study published in the Review of Economics and Statistics found, robbery rates fell. After Daylight Saving Time started in the spring, there was a 27 percent drop in robberies during that extra hour of evening sunlight, and a 7 percent drop over the course of the whole day.

6. YOU CAN GO OUTSIDE.

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Warmer temperatures mean you can spend more time outside without freezing your feet off, which is great for mental health. Across the seasons, research has found that taking walks in nature slows your heart rate and makes you more relaxed, but some research indicates that there is something special about spring's effect on your brain. A 2005 study from the University of Michigan linked spending 30 minutes or more outside in warm, sunny spring weather to higher mood and better memory. But the effect reverses when spring ends, since being outside in the warmest days of summer is usually pretty uncomfortable.

7. IT MAKES YOU MORE CREATIVE.

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That same University of Michigan study found that spending time outside in the sunny spring weather isn't just a mood booster, it actually can change the way people think. The researchers found that being outdoors broadened participants' minds, leaving them more open to new information and creative thoughts.

8. THE LEAVES COME BACK.

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Spring brings green growth back to plants and trees. Depending on where you live, trees may begin sporting new leaves as early as mid-March. That successful spring leaf growth ensures a cool canopy to relax under during the hot summer—a hugely important factor in keeping cities comfortable. According to researchers, vegetation plays a big role in mitigating the urban heat island effect. When trees release water back into the air through evapotranspiration, it can cool down the areas around them by up to 9°F, according to the EPA.

9. GROWING PLANTS ABSORB CARBON DIOXIDE.

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It's amazing what a little sun can do for plants and grass. Through photosynthesis, plants convert sunlight, carbon dioxide, and water into food, releasing oxygen in the process. That means as plants start to grow in the spring, they pull carbon out of the atmosphere, providing an important environmental service. Plants take in roughly 25 percent of the carbon emissions humans produce, absorbing more than 100 gigatons of carbon through photosynthesis each growing season. Because of this, the amount of carbon dioxide in the atmosphere drops each spring and summer. (Unfortunately, it rises in the winter, when most plants aren't growing.)

10. IT'S EASY TO FIND FRESH PRODUCE.

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Many vegetables and some fruits are harvested in the spring. 'Tis the season to get your local asparagus, greens, peas, rhubarb, and other fresh produce. Getting more fruits and vegetables into your diet isn't just good for the body; it's good for the soul. A 2016 study of more than 12,000 Australians found that when people increased the amount of fruits and vegetables in their diet, they felt happier and had higher rates of life satisfaction. If they increased their intake by eight portions a day (a tall order, we know) the psychological gains were equivalent to the change in well-being people experience when they go from being unemployed to having a job, the researchers found.

11. FLOWERS ARE IN BLOOM.

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After months spent conserving energy, flowers bloom in the spring, once they sense that the days have grown longer and the weather has turned warmer. That's good for humans, because several studies have shown that looking at flowers can make you happy. A 2008 study of hospital patients found that having flowers in the room made people feel more positive and reduced their pain and anxiety [PDF]. Another study from Rutgers University found that when participants were presented with a bouquet of flowers, it resulted in what scientists call a "true smile" a full 100 percent of the time. Seeing flowers had both "immediate and long-term effects" that resulted in elevated moods for days afterward, according to the researchers [PDF].

12. YOU CAN TAKE YOUR EXERCISE ROUTINE OUTDOORS.

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While it's important to keep moving no matter what the weather, research shows that working out can be more beneficial if you do it outside. A 2011 study found that, compared with an indoor workout, exercising outdoors in nature increased energy levels, made people feel revitalized, and decreased tension, among other positive effects. People who worked out in the fresh air also tended to say they enjoyed the experience more and would be likely to repeat it, suggesting that using nature as your gym might help you stick with your exercise regimen. While those benefits probably extend to winter, too, it's a whole lot easier to stomach the idea of a run once the weather warms up.

13. YOU DON'T HAVE TO WORRY ABOUT DRY AIR.

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Flu season in the U.S. typically lasts through the fall and winter, usually peaking between December and February and tapering off during the spring. The seasonal change is in part because of dry air. Cold temperatures mean a drop in humidity, and indoor heating only makes the air drier. This lack of moisture in the air can dry out your skin and the nasal cavities, leading to nose bleeds, irritated sinuses, and a greater risk of getting sick. Since the mucus in your nose is designed to trap viruses, when it dries up, you're more likely to catch something nasty, like the flu. As the weather warms up and becomes more humid throughout the spring, that mucus comes back. As the season wears on, not only can you lay off the body lotion, but you can probably put away the tissues—if you don't have spring allergies, that is.

14. YOU CAN OPEN YOUR WINDOWS.

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Temperate weather makes it easier to get the fresh air you need. Opening your windows and allowing the breeze in serves as an important way to ventilate indoor spaces, according to the EPA. A lack of ventilation can lead to an unhealthy concentration of indoor pollutants from sources like cleaning product fumes, certain furniture and building materials, and stoves (especially gas ones), posing a threat to your health and comfort. Winter brings the highest rates of indoor pollutants like nitrogen oxide, a 2016 study of unventilated stove use in homes found. Spring brings the perfect opportunity to throw open those windows and doors and get the air moving again.

15. YOU CAN GET YOUR VITAMINS NATURALLY.

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Sunlight triggers your body to produce vitamin D, which keeps your bones strong. At northern latitudes, it's extremely difficult to get enough sun exposure naturally to maintain healthy vitamin D levels during the winter—even if you did want to expose your skin to the elements—but that starts to change during the spring. One Spanish study found that in Valencia (which shares a latitude with Philadelphia, Denver, Baltimore, Kansas City, and several other major U.S. cities), people only need 10 minutes outside with a quarter of their bodies exposed to the spring sunshine to get an adequate daily dose of vitamin D.

A version of this story originally ran in 2014.

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High-Speed Railway Project Uncovers a Prehistoric Coastline Near London
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UK engineers have discovered evidence of a prehistoric coastline just outside London while preparing for a new high-speed railway, The Guardian reports.

The UK government has been analyzing the ground at the proposed locations for the railway, HS2, since 2015. Engineers are using radar, taking core samples, and digging pits before Phase 1 of construction. While evaluating the site of a future tunnel, geologists found signs that the site in the West London area of Ruislip was once a coastal marsh. Almost 110 feet under the ground, they discovered black clay they believe was formed from wooded swampland on the coast of a subtropical sea.

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The unusually well-preserved layer of clay, which features traces of vegetation, dates back to around 56 million years ago, when Great Britain was partially covered by a warm sea. Less than 200 feet away from where the black clay was discovered, the layer of earth at the same depth is made of sand and gravel, likely deposited by the sea.

"Although ground investigations regularly take place across the country, it's really exciting and very unusual to come across a material that no one has ever seen before," geological expert Jacqueline Skipper said in a press release from HS2. "The 'Ruislip Bed' discovery is particularly fascinating, as it is a window into our geological history." While researchers knew that much of England was underwater during this period, this evidence helps them pinpoint exactly where that sea began.

[h/t The Guardian]

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