Jud Ready, Georgia Institute of Technology

Imagine – it’s the mid-1800s, and you’re riding your high-wheeled, penny-farthing bicycle down a dusty road. Sure, it may have some bumps, but if you lose your balance, you’re landing on a relatively soft dirt road. But as the years go by, these roads are replaced with pavement, cobblestones, bricks or wooden slats. All these materials are much harder and still quite bumpy.

As paved roads grew more common across the U.S. and Europe, bicyclists started to suffer gruesome skull fractures and other serious head injuries during falls.

As head injuries became more common, people started seeking out head protection. But the first bike helmets were very different than helmets of today.

I’m a materials engineer who teaches a course at Georgia Tech about materials science and engineering in sports. The class covers many topics, but particularly helmets, as they’re used in many different sports, including cycling, and the materials they’re made of play an important role in how they work. Over the decades, people have used a wide variety of materials to protect their heads while biking, and companies continue to develop new and innovative materials.

In the beginning, there was the pith helmet.

Pith helmets

The first head protection concept introduced to the biking world was a hat made from pith, which is the spongy rind found in the stem of sola plants, aeschynomene aspera. Pith helmet craftsmen would press the pith into sheets and laminate it across dome-shaped molds to form a helmet shape. Then, they’d cover the hats in canvas as a form of weatherproofing.

Pith helmets were far from what we would consider a helmet today, but they persisted until the early 20th century, when bicycle-racing clubs emerged. Since pith helmets offered little to no ventilation, the racers began to use halo-shaped leather helmets. These had better airflow and were more comfortable, although they weren’t much better at protecting the head.

Leather halo helmets

The initial concept for the halo helmet used a simple leather strip wrapped around the forehead. But these halo helmets quickly evolved, as riders arranged additional strips longitudinally from front to back. They wrapped the leather bands in wool.

For better head protection, the helmet makers then started adding more layers of leather strips to increase the helmet’s thickness. Eventually, they added different materials such as cotton, foam and other textiles into these leather layers for better protection.

While these had better airflow than the pith hats, the leather “hairnet” helmets continued to offer very little protection during a fall on a paved surface. And, like pith, the leather helmets degraded when exposed to sweat and rain.

Despite these drawbacks, leather strip helmets dominated the market for several decades as cycling continued to evolve throughout the 20th century.

Then, in the 1970s, a nonprofit dedicated to testing motorcycle helmets called the Snell Foundation released new standards for bike helmets. They set their standards so high that only lightweight motorcycle helmets could pass, which most bicyclists refused to wear.

New materials and new helmets

The motorcycle equipment manufacturing company Bell Motorsports responded to the new standards by releasing the Bell Biker in 1975. This helmet used expanded polystyrene, or EPS. EPS is the same foam used to manufacture styrofoam coolers. It’s lightweight and absorbs energy well.

Constructing the Bell Biker involved spraying EPS into a dome shaped mold. The manufacturers used small pellets of a very hard plastic – polycarbonate, or PC – to mold an outer shell and then adhere it to the outside of the EPS.

Unlike the pith and leather helmets, this design was lightweight, load bearing, impact absorbing and well ventilated. The PC shell provided a smooth surface so that during a fall, the helmet would skid along the pavement instead of getting jerked around and caught, which could cause abrupt head rotation and lead to concussions and other head and neck injuries.

Over the next two decades, as cycling became more popular, helmet manufacturers tried to strike the perfect balance between lightweight and ventilated helmets, while simultaneously providing impact protection.

In order to decrease weight, a company called Giro Sport Design created an all-EPS helmet covered by a thin lycra fabric cover instead of a hard PC shell. This design eliminated the weight of the PC shell and improved ventilation.

In 1989, a company called Pro Tec introduced a helmet with a nylon mesh infused in the EPS foam core. The nylon mesh dramatically increased the helmet’s structural support without the added weight of the PC shell.

Meanwhile, as cycling became more competitive, many riders and manufacturers started designing more aerodynamic helmets using the existing materials. A revolutionary teardrop style helmet debuted in the 1984 Olympics.

Now, even casual biking enthusiasts will don teardrop helmets.

Helmets on the market today

Helmet makers continue to innovate. Today, many commercial brands use a hard polyethylene terephthalate, or PET, shell around the EPS foam in place of a PC shell to increase the helmet’s protection and lifespan, while decreasing cost.

Meanwhile, some brands still use PC shells. Instead of gluing them to the EPS foam, the shell serves as the mold itself, with the EPS expanding to fit inside it. Manufacturing helmets this way eliminates several process steps, as well as any gaps between the foam and shell. This process makes the helmet both stronger and cheaper to manufacture.

As helmets evolve to provide more protection with still lighter weight, materials called copolymers, such as acrylonitrile-butadiene-styrene, are replacing PC and PET shell materials.

Materials that are easier and cheaper to manufacture, such as expanded polyurethane and expanded polypropylene, are also starting to replace the ubiquitous EPS core.

Just as the leather and pith helmets would look strange to a cyclist today, a century from now, bike helmets could be made with entirely new and innovative materials.

Jud Ready, Principal Research Engineer in Materials Science and Engineering, Georgia Institute of Technology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Beth Ann Malow, Vanderbilt University

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.

Why do I feel better rested when I wake myself up than I do if my alarm or another person wakes me up? – Calleigh H., age 11, Oklahoma

We’ve all experienced this: You’re in the middle of a lovely dream. Perhaps you’re flying. As you’re soaring through the air, you meet an eagle. The eagle looks at you, opens its beak and – BEEP! BEEP! BEEP!

Your alarm goes off. Dream over, time to get up.

Many people – kids and adults alike – notice that when they wake up naturally from sleep, they feel more alert than if an alarm or another person, like a parent, wakes them up. Why is that?

I’m a neurologist who studies the brain, specifically what happens in the brain when you’re asleep. I also take care of children and adults who don’t sleep well and want to sleep better. My research involves working with parents to help them teach their children good sleep habits.

To understand how to sleep better, and why waking up naturally from sleep helps you feel more alert, you need to start by understanding sleep cycles.

The sleep cycle

The sleep cycle consists of four stages. One of these is REM, which stands for rapid eye movements. The other three are non-REM stages. When you fall asleep, you first go into a state of drowsiness called non-REM Stage 1.

This is followed by deeper stages of sleep, called non-REM stages 2 and 3. Each stage of non-REM is deeper than the one before. Then, about 90 minutes after you first fall asleep, you enter the fourth stage, which is REM sleep. This is a stage of lighter sleep where you do much of your dreaming. After a few minutes, you return to non-REM sleep again.

These cycles repeat themselves throughout the night, with most people having four to six cycles of non-REM sleep alternating with REM sleep each night. As the night goes on, the cycles contain less non-REM sleep and more REM sleep. This is why it’s important to get enough sleep, so that the body can get enough of both REM sleep and non-REM sleep.

REM vs. non-REM sleep

How do researchers like me know that a person is in non-REM vs. REM sleep? In the sleep lab, we can tell from their brain waves, eye movements and the tension in their muscles, like in the chin. These are measured by putting sensors called electrodes on the scalp, around the eyes and on the chin.

These electrodes pick up brain activity, which varies from waves that are low in amplitude (the height of the wave) and relatively fast to waves that are high in amplitude (a taller wave) and relatively slow. When we are awake, the height of the waves is low and the waves are relatively fast. In contrast, during sleep, the waves get higher and slower.

Non-REM Stage 3 has the tallest and slowest waves of all the sleep stages. In REM sleep, brain waves are low in amplitude and relatively fast, and the eye movements are rapid, too. People need both non-REM and REM stages for a healthy brain, so they can learn and remember.

Waking up naturally

When you wake up in the morning on your own, it’s usually as you come to the end of whatever stage of sleep you were in. Think of it like getting off the train when it comes to a stop at the station. But when an alarm or someone else wakes you up, it’s like jumping off the train between stops, which can feel jolting. That’s why it’s good to wake up naturally whenever possible.

People can actually train their brains to wake up at a consistent time each day that is a natural stopping point. Brains have an internal 24-hour clock that dictates when you first start to feel sleepy and when you wake up. This is related to our circadian rhythms.

Training the brain to wake up at a consistent time

First, it’s important to go to bed at a consistent time that allows you to get enough sleep. If you stay up too late doing homework or looking at your phone, that can interfere with getting enough sleep and make you dependent on an alarm – or your parents – to wake you up.

Other things that can help you fall asleep at a healthy time include getting physical activity during the day and avoiding coffee, soda or other drinks or foods that contain caffeine. Physical activity increases brain chemicals that make it easier to fall asleep, while caffeine does the opposite and keeps you awake.

Second, you need to be aware of light in your environment. Light too late in the evening, including from screens, can interfere with your brain’s production of a chemical called melatonin that promotes sleep. But in the morning when you wake up, you need to be exposed to light.

Morning light helps you synchronize, or align, your circadian rhythms with the outside world and makes it easier to fall asleep at night. The easiest way to do this is to open up your shades or curtains in your room. In the winter, some people use light boxes to simulate sunlight, which helps them align their rhythms.

Benefits of a good night’s sleep

A good sleep routine entails both a consistent bedtime and wake time and regularly getting enough sleep. That usually means 9-11 hours for school-age kids who are not yet teens, and 8-10 hours for teens.

This will help you be at your best to learn at school, boost your mood, help you maintain a healthy weight and promote many other aspects of health.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Beth Ann Malow, Professor of Neurology and Pediatrics, Vanderbilt University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Mark Boslough, University of New Mexico

With the Taurid meteor shower now hitting the night skies worldwide, look for what could be a celestial treat – you might see shooting stars, and maybe even fireballs, the biggest and brightest meteors.

As the full moon begins to wane after Nov. 15, the sky will be darker, due to diminishing moonlight, so finding the meteors will get easier. That said, the best visibility for the meteors through the rest of the month will come just before moonrise each night.

Beyond the light show, there is something else that scientists as well as onlookers have long wondered about: the possibility that bigger chunks are in the Taurid meteor streams, chunks the size of boulders, buildings or even mountains.

And if that’s true, could one of those monster-sized Taurid objects collide with Earth? Could they wipe out a city, or worse? Is it possible that’s already happened, sometime in our planet’s past?

As a physicist who researches the risk that comets and asteroids pose to the Earth, I’m aware that this is a subject where pseudoscience often competes with actual science. So let’s try to find the line between fact and fiction.

Pig Pen, glowing tails and shooting stars

Comet Encke is the so-called parent comet of the Taurid meteors. It’s relatively small, just over 3 miles (almost 5 kilometers) in diameter, and crosses inside Earth’s orbit and back out every 3.3 years.

As Encke moves, it sheds dust wherever it goes, like the Peanuts character Pig Pen. A meteor shower occurs when that dust and debris light up while entering Earth’s atmosphere at high speeds. Ultimately, they vanish into an incandescent puff of vapor with a glowing tail, creating the illusion of a “shooting star.”

But dust isn’t all that breaks off the comet. So do bigger chunks, the size of pebbles and stones. When they collide with the air, they create the much brighter fireballs, which sometimes explode.

Doomsday showers

The “coherent catastrophism” hypothesis suggests that comet Encke was created when an even larger comet broke up into pieces; Encke survived as the largest piece. The hypothesis also suggests that other mountain-sized chunks broke off and coalesced into a large swarm of fragments too. If such a swarm exists, there is a possibility that those large chunks could one day hit Earth as it passes through the swarm.

But just because something might be physically possible doesn’t mean that it exists. Mainstream astronomers have rejected this theory’s most catastrophic predictions. Among other reasons, scientists have never observed high concentrations of these mountain-sized objects.

Despite the lack of evidence, researchers on the fringes of science have embraced the idea. They claim the Earth experienced a global catastrophic swarm 12,900 years ago; the impact, they say, caused continent-wide firestorms, floods and abrupt climate change that led to the mass extinction of large mammals, such as woolly mammoths, and the disappearance of early Americans known as the Clovis people.

The evidence for a catastrophic cause of these events, most of which did not happen, is lacking. Nevertheless, the idea has gained a large following and formed the basis for British author Graham Hancock’s popular TV series, “Ancient Apocalypse.”

The Tunguska event

But even outlandish ideas can have elements of truth, and there are hints that some objects – more than just dust and debris, but less than doomsday size – indeed exist in the Taurid meteor stream, and that the Earth has already encountered them.

One clue comes from an event on June 30, 1908, when an enormous explosion in the sky blew down millions of trees in Siberia. This was the Tunguska event – an airburst from an object that may have been up to 160 feet (about 50 meters) in diameter.

The collision unleashed several megatons of energy, which is roughly the equivalent of a large thermonuclear bomb. What happens is this: The incoming object penetrates deep into Earth’s atmosphere, and the dense air slows it down and heats it up until it vaporizes and explodes.

Could this object have been a Taurid? After all, the Taurids cross Earth’s orbit twice a year – not just in autumn, but also in June.

Here’s the evidence: First, the descriptions of the trajectory of the Tunguska airburst, as reported by eyewitness observers, is consistent with that of an object coming from the Taurid stream.

What’s more, the pattern of blast damage on the ground beneath an airburst depends on the trajectory of the exploding object. Supercomputer simulations show that the shape of the surface blast that would be caused by an exploding Taurid object matches the pattern of fallen trees at Tunguska.

Finally, during the Taurid meteor shower in 1975, people observed large fireballs – and seismometers, previously placed on the Moon by Apollo astronauts, detected seismic events on the lunar surface. Scientists interpreted those events as impacts, presumably made by the Taurid meteors.

In 2032 and 2036, the Taurid swarm – assuming it exists – is predicted to be closer to the Earth than any time since 1975. That might mean the Moon, and perhaps the Earth, could be pelted again in those years.

There is time to figure this out. Scientists can expand their astronomical surveys to look for Tunguska-sized objects at the locations where they are predicted to be the next time they are in our vicinity.

Most scientists remain skeptical that such a swarm exists, but it’s the job of planetary defenders to investigate possible threats, even if the risk is small. After all, a Tunguska-sized object could conceivably demolish a major city and kill millions; an accurate count of objects on a potential collision course is essential.

Put doomsday scenarios and ancient apocalypses aside. The real question, and still an open one, is whether a Taurid swarm could deliver more Tunguska-sized objects than would otherwise be expected. This would mean we have underestimated the risk from future airbursts.

Mark Boslough, Research Associate Professor of Earth and Planetary Sciences, University of New Mexico

This article is republished from The Conversation under a Creative Commons license. Read the original article.