TedEd: Which sunscreen should you choose?

By Mary Poffenroth

Many people know that sunscreen is important to prevent things like sunburn and cancer from UV radiation. But there are many different types of sunscreens, so how do they work, and how effective are they? The Sun emits three types of UV rays: UV A, UV B, and UV C. Ultraviolet light has shorter wavelengths than visible lights, which is what causes all of the bad effects like cancer, DNA damage, and sunburn. UV C has wavelengths so short that it is reflected by the atmosphere, but UV B can impact the skin, and UV A can go even deeper to blood and organs. Sunscreen prevents these effects by either physically blocking the UV rays or utilizing carbon-based chemicals to absorb the radiation. There are three factors to consider when choosing a sunscreen: application method, SPF, and active ingredients. Spray bottles go on easily when wet, but most people do not apply enough and the aerosol can be bad for health. SPF stands for sun protection factor, which is a nonlinear scale of the amount of UV B radiation needed to cause sunburn. 15 is the minimum recommended, but 30 and above is better. For chemicals, zinc and titanium oxide-based is usually less irritating to the skin. This is also better for the environment because carbon-based chemicals have been proven to be harmful to ocean life.

TedEd: The ancient origins of the Olympics

A TedEd by Armand D'Angour

In 776 BCE, the Olympic games first took place in the ancient Greek city of Olympia as a tribute to the Greek god Zeus. They believed that competition fosters excellence, so they held a variety of competitions like running, poetry, singing, and more. The first games began with the 200 yard dash, but the games quickly evolved to include boxing, chariot racing, the pentathlon, and other events. Then in 391 AD, during the Roman Empire, the Christian Roman Emperor Theodosius banned the Olympic games, ending the millenia long tradition. 1500 years later, in 1896, the first modern games began in Athens, Greece, bringing thousands of athletes from around the world together in the world's largest sporting event.

TedEd: Could we build a wooden skyscraper?

By Stefan Al

Mjøstårnet is an 18 story tall building towering over the forests of Norway. But this isn't just any old building - it's the tallest wooden building on Earth. But even at the end of the 20th century, scientists believed a wooden building couldn't get over 6 levels. This is because regular lumber could handle forces parallel to its grain very well, but not forces perpendicular, meaning it couldn't withstand the weight of a tall building or the wind at high altitudes. However, the late 1800s brought about the creation of glue-laminated timber (glulam), and a century later, cross-laminated timber (CLT) was invented. In glulam, boards are stacked on top of each other and in CLT, layers are oriented opposite to each other. This meant glulam had significantly more tensile strength and CLT could withstand forces in both directions. These types of building materials can be made more easily than steel or concrete, and they are less likely to be permanently damaged in a fire. Additionally, they could help lower the 11% share that the construction industry has in global warming. Still, CLT and glulam are not as strong as steel and concrete, and require more wood than traditional construction. It's unlikely that they will be strong enough to support true 40-story skyscrapers, but even building up to 30-stories with a mix of steel and concrete could significantly lower our carbon footprint.

TedEd: The benefits of a good night's sleep

A TedEd by Shai Marcu

When you have a big test or performance coming up, and you've been working for weeks, but you're still a little bit unsure, do you sleep or do you pull an all-nighter? It turns out that sleep is much more important, especially for memory, than we often think. Sleep is actually a key part of your brain's functions, including memory. During sleep, our brain goes through a restructuring in which neurological pathways are strengthened and weakened to help us remember things. Herman Ebbinghaus found in the 19th century that we usually forget about 40% of the things we learn in the first 20 minutes. We can prevent this loss by transferring short-term memories to long-term memory. A structure called the hippocampus helps with this, and its function was determined in the 1950s by Brenda Milner with a patient known as H.M. The patient's hippocampus was removed, their ability to form both long and short-term memories was impaired. However, they were still able to learn physical tasks through repetition. The hippocampus takes short-term memories from neurons and strengthens and forms new synaptic pathways to preserve these memories. Memories made in times of strong emotion are usually easier to remember. Sleep is another important part of memory, especially the 2 deepest stages, known as slow-wave and REM sleep. EEG readings taken during these times show high activity between the brainstem, hippocampus, thalamus, and cortex. So the saying "sleep on it" might really be effective after all.

TedEd: A brief history of toilets

A TedEd by Francis de los Reyes

In the days of the Roman Empire, people would go to communal bathrooms in order to talk and do their business. The waste would then drop down below into water pipelines. Though bathrooms today are a bit different, it is still an important invention. Most ancient texts describe some sort of advice about keeping waste away from water and shelter, and waste management began to take a more tangible form as early as 3000 BCE. As humans advanced, they formed squatting latrines in streets that connected to sewage, while houses in other areas each had their own toilets. These developments are key because untreated sewage is a breeding ground for a variety of diseases. During the Roman era, more sophisticated management systems were created that took sewage outside of city walls. In China, similar systems fed pigs and were sold as fertilizer. After the fall of the Roman Empire, Europe went through a dark age not only in general but of sanitization. People dumped waste into the streets and disease ran wild. But toward the end of the Middle Ages, conditions improved and most families had commode stools, or wooden boxes with lids, to do their business. In England, Sir John Harrington created the first modern flush toilet for Queen Elizabeth, and it largely follows the same mechanism we use today. In 1775, Alexander Cumming created an S-shaped bend in the pipes to retain water and keep out the smell, which was later improved to a U-bend by Thomas Crapper. Today, we also have wastewater management sites to ensure that the water released from toilets is clean and sanitary. But more than 4 billion people worldwide still lack a toilet or waste management.

TedEd: The sharks that hunt in forests

By Luka Seamus Wright

Most people don't imagine sharks hunting and living in trees. But marine forests cover 4.2 million square miles of the Earth, and many sharks live and find protection in the roots of mangroves, as well as hunt in seagrasses. They provide shelter to 35% of the world's shark population. Perhaps the most unique ecosystem is one created by the mangroves. Mangroves live both on land and at sea, and their unique roots house many animals. In order to live in this limbo, they have several adaptations. First, their seedlings develop in trees before dropping into the water in a semi-mature state and drifting to a location where they can take root. They use some form of skinny roots and prop roots to hold themselves above the water. These roots also have microscopic breathing pores that the mangroves use to take in oxygen and keep out saltwater. The roots often have filters for salt as well, while some species opt to store salt and excrete it. These trees form the foundation of ecosystems that house many organisms, as well as sharks. But grown, predatory sharks arent bad - they keep the numbers of other organisms in check so the ecosystem doesn't get overcrowded. Overfishing in recent years has placed many of these homes in peril, and humans need to fight in order to preserve them.

TedEd: How fast is the speed of thought?

By Seena Mathew

Imagine a scenario where an enemy has captured you and agrees to let you go if you win a contest. Your brain has been connected via one long neuron to a target. At some point, he will fire an arrow to the target, at which point you need to send a thought to the target before the arrow hits it. To determine if you can win, you need to know how fast your thought can move. 86 billion neurons make up your brain, and these cells have axons that move electrical signals along them. At the end, points called synapses transfer the signal to the dendrites of the next axon in the chain. The first part of figuring out your dilemma is finding out how long it takes to start an action potential (thought), then how fast it can travel down an axon. Based on how fast your knee jerk reaction takes, the average thought takes moves at around 240 km/h. But if an axon is wider or coated with a myelin sheath, it can travel faster, at around 432 km/h. These structures can also degrade with the onset of age. Since the arrow travels at 240 km/h, your thoughts could probably win the race. But you also need to know how long it takes for you to actually perceive the arrow, since you have to wait for the arrow to fire before sending your thought. Your eyes can see the arrow in about 13 milliseconds, but it will take another 200 milliseconds for your brain to process it, giving the arrow a head start of 13 meters. But because your thoughts are faster, they might just be fast enough to win the race.

TedEd: What happens when you have a concussion?

A TedEd by Clifford Robbins

Each year in the U.S., millions of athletes get concussions. A concussion occurs when the soft, fatty tissue of the brain receives a sudden jolt and bumps against the side of the hard skull. The brain is made up of tens of billions of neurons, which transfer electrical signals to communicate throughout the body via axons. Because these axons are long and thin, they are prone to breaking when collisions occur. This also releases toxins that kill other neurons nearby, causing more brain damage. This often results in problems with memory, mood, vision, sleep, and anxiety. Most of the time, sleep, rest, and a gradual return to activity heals most side effects of concussions. Sometimes, if people return to sports too quickly or don't rest, they can develop post-concussion syndrome, which has health implications years down the line. Researchers also found that frequent, small impacts can cause the brain to loose integrity in its axon bundles, leading to chronic traumatic encephalopathy, which can cause concussion-like symptoms along with dementia. This occurs due to a protein called tau, which is usually on microtubules supporting the axons. However, when impacted, they fall off and form clumps, impeding axon efficiency. Up 80% of concussions go undetected or unreported, and it's important to remember that our brains aren't invincible.

TedEd: What makes muscles grow?

A TedEd by Jeffrey Siegel

There are over 600 muscles in our body that hold us together and allow us to move. Most people know that the way you treat them on a daily basis determines whether they grow or shrink. Muscles work by receiving electrical signals from the brain via neurons, which causes them to contract or loosen. If a task is harder, the brian puts more muscles to use. With most everyday tasks, your muscles experience easy loads. But when it encounters a difficult task, the muscles strain, causing microscopic damage. This might sound bad, but it's actually how muscles grow. Your immune system deploys cytokines to the damaged area to rebuild the muscle, causing that muscle to grow. When your muscles are not exposed to consistent strain, they shrink in a process called muscular atrophy. Putting your muscles in high tension, especially when they are lengthened (eccentric contraction) causes them to grow. In addition to exercise, muscles need rest and nutrition to grow. They need proteins you consume with your food, as well as hormones like testosterone that encourage growth. There are also genetic factors because some people have a more robust immune system to facilitate muscle growth.

TedEd: How tsunamis work

By Alex Gendler

Tsunamis are often called "tidal waves", but this is a misnomer. They are not caused by the pull of the moon, but rather by energy moving through the water, just like with regular waves. The reason they are bigger is that the source and strength of energy are different. Rather than being moved by wind, which can only produce so much power, tsunamis are caused by massive tremors underground, such as earthquakes and volcanos. When this force makes its way to the surface, it causes a massive spike in the water which then crashes down and sends energy in all directions. The waves seem normal in open oceans, but when they get to shallow water, the energy is compressed and this brings the tsunami up high over the water. Even with innovations like flood walls and channels, tsunamis can cause damage up to a mile inland and destroy everything in their path. The best thing to do in case of a tsunami is to get out of its way (i.e. high up or out of range).

TedEd: How one design flaw almost toppled a skyscraper

A TedEd by Alex Gendler

In 1978, Diane Hartley was writing her architectural thesis when she discovered something shocking. The Citicorp Center had a fatal flaw in its building plans that could cause it to tumble into a densely populated area. The flaw stemmed from the building's unique structure. The building site was partially occupied by a church, so it was supported by 4 columns. Because the church was at the corner of the block, those columns were also in the middle of each side of the building, rather than the corners. This worried many people, but the architect William LeMessurier used both a 400-ton mass damper and a V-shaped chevron exoskeleton to ensure the building met safety standards. However, the builders assumed that the building would be getting the most wind from the sides. What Hartley found was that because of the positioning of the base, the most stress would actually be on the corners of the building. LeMessurier had built the skyscraper with this in mind, but when he looked at the building plans again, he found that there had been a fatal change he hadn't been informed of. The joints of the exoskeleton were bolted rather than welded, decreasing structural integrity so much that a strong storm could bring it down. A secret plan was launched with the city to weld the joints at night. Construction was completed without the press knowing because it was completed in the midst of a strike. Only years later did magazines and Diane Hartley find out just how close the building had been to falling.

TedEd: The infinite life of pi

A TedEd by Reynaldo Lopez

If you were to measure the parts of a circle, how would you do it? The radius and diameter can simply be measured with a ruler, and the circumference would be a bit more complicated, perhaps requiring a tape measure. But there is actually a very important relationship between the circumference and diameter. The ratio of the two is what is known as pi. Although it is unknown when this relation was first discovered, we can see evidence of it going back 4,000 years. It can be found in ancient Greek, Babylonian, Chinese, and Indian texts, and is even believed to have been used in building the pyramids. Mathematicians estimated it by inscribing polygons in circles, but we will never be able to get an exact value for it. This is because pi is an irrational number, or cannot be expressed as the ratio of two whole numbers. So in decimal form, pi is an endless series of digits starting with 3.14159. For everyday usage, we write it as π instead of an infinite string of numbers, and there are even world records for memorizing the most numbers. Pi is used in all calculations involving circles, and it can also be used for curves and oscillations like clocks and music. In statistics, it is used in the calculation of a normal distribution curve, and it has been used in physics for the Hadron Collider and proof of the wave-particle duality of light. In fact, it has even been used to calculate the total density of our universe!

TedEd: Performing brain surgery without a scalpel

Hyunsoo Joshua No

Thousands of people each year undergo brain surgery without an operation. A new procedure called stereotactic radiosurgery works by using beams of radiation to wear away malignant cells. The procedure involves a series of CT-scans that determine the location and size of the tumor. For some patients, an additional MRI may be needed. CT-scans also calculate the Hounsfield units of various parts of the brain, which shows the density of a material. This is important because this determines how radiation will spread through the brain. Radiosurgery uses multiple beams of radiation that converge on a tumor and destroy it. This is also helpful for doctors because they can change the angle and intensity of each beam to avoid surrounding brain structures. When the beams hit a cancer cell, they essentially cut their DNA into pieces, which causes the malignant cell to break down and eventually die. The radiation also breaks down molecules in the brain and produce unstable products called free radicals that create a poisonous environment for the cells. The immune system then cleans up the dead cells and produces scar tissue. However, there are multiple restrictions on radiosurgery. It is generally used in very small areas, and because radiation adds up in the body, recurring treatments are risky. Still, the benefits often outweigh the risks. Its success rate is as high as normal surgery for many diseases, and it requires little to no recovery time or pain.

TedEd: A brief history of plastic

A TedEd by the TedEd team

Plastics are endemic to society. But they first came from a round object that wasn't even made of plastic - billiard balls. Billiard balls used to be made from elephant tusk ivory. But overhunting led to a decline in elephant populations, and ball manufacturers posted huge rewards for a new material. In 1863, American scientist John Wesley Hyatt decided to try. For 5 years, he worked to create celluloid, made from a compound in wood and straw called cellulose. Unfortunately, celluloid wasn't heavy enough and didn't bounce the right way to replace ivory in billiard balls. But it could be tinted and patterned to resemble other materials. Plastics are polymers - long molecules made of repeating parts. Plastics are soft and can be easily molded. The first plastic, celluloid, was unfortunately highly flammable, making it less useful. In 1907, Bakelite was created from a mix of phenol and formaldehyde. Since phenol came from the remnants of coal tar, it was cheaper to make, and it was less flammable. In the decades that followed, many other plastics came out, and polyethylene, developed in 1933, is still very commonly used. Injection molding was also created, and it allowed for plastics to be formed in the same mold over and over, opening up an array of possibilities. Surprisingly, plastics were first widely used in World War II, when they were used to make a variety of equipment, rather than to make consumer products. After the war, the factories began making consumer products like furniture and packaging. Unfortunately, the new ease and low costs also came with massive environmental impacts because plastics use many nonrenewable resources and take a very long time to decompose. Scientists today are working on more renewable materials and recycling what we already have.

TedEd: The beneficial bacteria that make delicious food

A TedEd by Erez Garty

Have you ever wondered where cheese and bread get their holes, and how wine and vinegar are made? They are all made from microscopic organisms that eat the sugar inside the food. Yeast is a unicellular fungus that requires carbohydrates to function. It is used to make bread, wine, and beer, and has two ways to process the carbohydrates. The aerobic pathway requires oxygen, whereas the anaerobic method does not. The latter is also known as fermentation, which is what yeast usually uses first when making bread. This process creates CO2 and ethanol. The aerobic process creates both CO2 and water, and the ethanol evaporates while the CO2 makes the little bubbles in bread that give it its fluffiness. When wine is made, oxygen levels are lowered so that yeast ferments to produce alcohol, and the CO2 is either released or concentrated for carbonated beverages. Wine also uses other types of bacteria to turn tart grape juice into the signature taste of red wines and chardonnays. However, a different type of bacteria, which produces acetic acid from the ethanol in wine in the presence of oxygen. This turns the wine into vinegar. Milk is inoculated with another type of bacteria to create cheese; the bacteria turn lactose into lactic acid, which causes milk to curdle. An enzyme called rennet can speed up the process, and the curdles become curds, which are squeezed to remove water and become cheese. In some cheeses, mold is added.

TedEd: Why people fall for misinformation

A TedEd by Joseph Isaac

A misconception is something that is commonly believed by largely incorrect, for example, the taste map discovered by David Hänig in 1901. The simplified versions printed in many books and newspapers were incorrect. There are two common types of misconceptions. One is disinformation, which is fake information designed to mislead people. However, misinformation is more common, and it is inaccurate information that is unintentionally created. So why do we fall for misconceptions so easily? Misinformation often occurs from human error in transmission, like a game of telephone, which is what happened to Hänig's taste map. It was written in German and academic language, so it was hard to understand for most people. So, newspapers began reporting that certain flavors were imperceptible on certain parts of the tongue, whereas Hänig's research showed that flavors were present on all parts of the tongue and the areas he identified were only slightly more sensitive to certain flavors. Another factor in the spread of this misconception was the simplification of Hänig's complicated diagram, which was more approachable and fits our ideal of being able to understand the world. However, science is often more complicated than that, and a good story is often hard to ignore. So the next time you see some amazing fact, make sure you know it's really true.

TedEd: The fish that walk on land

A TedEd by Noah R. Bressman

A walking catfish can jump out of the water if it wants to go somewhere new. Of course, many dangers come with this. Death by dehydration, physical dangers, and predators are all in the mix. This may seem odd, but there are actually hundreds of species of fish that are amphibious or can live on land and in the water. Some types only do this when necessary, while it is a part of life for others. Some fish come out of the water when it is too hot and stay moist in the shade. The walking catfish comes out to eat bugs, and California grunion comes ashore to mate. Normally, fish use gills to breathe, which are feathery organs filled with blood vessels that absorb the oxygen in the water. However, the gills collapse when outside the water. So, some fish have oxygen-absorbing parts inside their bodies or actual lungs. Fish also have thin skin that nutrients can pass through, which makes them dry up outside water. So, some fish flop around in the mud, while others coat themselves in mucus and go deep into the earth. The fins of amphibious fish are extra-strong, enabling them to move around on land. But how do they navigate? Some fish look for reflective surfaces, while others move downward in hopes that water will be downhill. More sophisticated animals like the walking catfish have a lot of taste buds on their whiskers, which it uses to detect prey, water, and harmful areas. So while amphibious fish may have a hard time out of the water, they have evolved ways to solve this over time to become the amazing creatures they are today.

Side note: This actually ties into what I am learning at school, evolution and natural selection.

TedEd: What was so special about Viking ships?

A TedEd by Jan Bill

The Vikings had few of the typical markers of successful civilizations. They had no centralized government or money and came from one of the most inhospitable places on Earth in Scandanavia. Their secret? Ships. Although it began as a typical hollowed out canoe, the Viking longship became one of the greatest in the world. They had always used ships because the mountainous terrain and dense forests of Scandanavia made overland travel difficult. However, there were plenty of waterways to travel on. The first log boats began their evolution when planks were added to the base in the clinker, or "lapstrake" technique in which the planks are overlapped and were connected at their edges. Some Scandanavians also served in the Roman army and brought back the technology of Roman war and merchant ships. The log bottom was abandoned for a keel plank, an interior framework was added with the use of nails, and the oars were fastened. Still, their ships were light because they depended on a strong shell rather than the interior. They also didn't have any sails because those were expensive and unnecessary at that point. However, after the collapse of the Roman empire, trade routes were extended to Scandanavia, and chieftains needed sailing ships to effectively control these money-making routes. So by the 700's, sails were added to go further and faster. By the end of the 9th century, the Viking ship most people know today was created. These longships could land on beaches and go upriver, and there were smaller and larger versions for various amounts of cargo on trade expeditions. With these new innovations, the Vikings traveled where no one from Europe had ever gone - North America.

TedEd: Should you trust unanimous decisions?

A TedEd by Derek Abbott

Many of us are inclined to believe unanimous decisions. But although they seem very strong, they aren't as infallible as we think. Much of our society relies on majority consensus, which can be a good thing sometimes. But at a certain point, getting closer to consensus gets us farther from the actual results. This is the Paradox of Unanimity. In cases with an obvious answer, unanimity is normal. But when there is some natural variance, there should also be some varied distribution. For instance, a bunch of coin tosses is expected to come up heads around 50% of the time. But it would be suspicious if they started nearing 100%, and you might suspect tampering with the coin. In fact, a study in the 1990's showed that nearly half of witnesses pick the wrong suspect. This is because our short term memory is only so good, and our brain automatically fills in gaps. There can also be systemic errors aside from human judgement; for example, accidental contamination of cotton swabs used by police led to the same DNA being found in many different crime scenes. And, of course, there is outright fraud itself, often occurring in politics. Still, unanimity is useful in situations with low variation, just not in ones with high probability of variation. In the latter, there is probably an external influence.

TedEd: Is the weather actually becoming more extreme?

A TedEd by R. Saravanan

In the past 40 years, the number of extreme weather events has been steadily increasing. But the question is, are these just bad weather patterns, or deeper changes to our climate? First, we should define the differences between weather and climate. Weather is defined as the atmospheric conditions at a specific point in time and a place. Right now, we can get fairly accurate weather predictions for about a week. Climate is the atmospheric condition in a region over a much longer period of time. Climate forecasts predict average weather patterns over time instead of specific types of weather. These two things are forecasted using different data sets. For weather, the conditions used are current precipitation, air pressure, humidity, and wind speed and direction. Twice a day, weather balloons with devices called radiosondes are released into the air to measure these conditions and transmit them to weather stations. Meteorologists can use this data in models that generate the forecast you see. The reason they are sometimes inaccurate is that weather is a chaotic system that is very sensitive to tiny details that are near impossible to have. Within just weeks, small changes in conditions can change weather patterns, like the butterfly effect. Climate forecasts are different, partially because they take an average of weather patterns and because they base their data on the range of possible outcomes. These boundary conditions constrain the possible weather and climate patterns. We can average these to get accurate climate models for years to come. The catch is that small changes to boundary conditions can make affect the chaotic weather systems. For example, the 1 degree celsius that the Earth's temperature has increased by has had the effect of 1M nukes in our atmosphere. These shifts do, in fact, increase the amount of extreme weather on our planet. This is what climate change is, but we can help combat it by examining changing boundary conditions and figuring out how to reverse our effects on the planet.