The crazy story of the arbitrary temperature scale used in a tiny minority of countries.
Check out Audible: http://bit.ly/AudibleVe
Snatoms are available again! http://www.snatoms.com
Support Veritasium on Patreon: http://bit.ly/VePatreon

Celsius didn't invent Celsius: http://bit.ly/VeCelsius

Video animated by Marcello Ascani: http://bit.ly/VeMarcello

Thanks to Patreon supporters:
Nathan Hansen, Bryan Baker, Donal Botkin, Tony Fadell, Saeed Alghamdi

Music by Kevin MacLeod: http://incompetech.com "Modern Piano Zeta - Improbable" "Ice Demon" "Divertimento K131" "Sneaky Adventure" "Sheep May Safely Graze" "Professor and the Plant"

References:
A History of the Thermometer and its uses in Meteorology by W. E. Knowles Middleton

Absolute Zero and the Conquest of Cold by Tom Shachtman

The Science of Measurement, A Historical Survey by Herbert Arthur Klein

Lehrbuch der Chemie by Jöns Jakob Berzelius

Script:
As an Australian-Canadian the Fahrenheit temperature scale always seemsed a bit arbitrary. I mean why does water freeze at 32 degrees? And what exactly does zero represent?

According to many sources the Fahrenheit scale was defined by setting zero degrees equal to the temperature of an ice, salt, and water mixture and 100 degrees being roughly equal to human body temperature. But that isn’t true.

The real story is much more interesting, and scientific...

August 14th 1701 was almost certainly the worst day in the life of fifteen year-old Daniel Gabriel Fahrenheit. On that day both of his parents died suddenly from mushroom poisoning. He was sent from Poland, where he lived, to Amsterdam to become an apprentice bookkeeper.

But Fahrenheit couldn’t stand his apprenticeship and ran away so many times his employers put out a warrant for his arrest. Traveling from city to city around Europe, he became fascinated with scientific instruments and in particular thermometers.

In 1708, possibly seeking help with the warrant, Fahrenheit met with the mayor of Copenhagen, who happened to be the famous astronomer Ole Romer.

Romer is known for observing the eclipses of Jupiter’s moons and realizing that variations in the timing of those eclipses was caused by the time it took light to reach Earth. In other words, he found a way to accurately measure the finite speed of light.

But more pertinent to this story, in 1702 Romer was housebound after breaking his leg. To pass the time he devised a new temperature scale with the freezing point of water at 7.5 degrees and body temperature at 22.5 degrees.

This might seem odd until you consider that Romer wanted the boiling point of water to be 60 degrees (as an astronomer, he had experience dividing things by 60). If you take this scale, divide it in half, in half again, and in half once more, you find the freezing point of water 1/8th up the scale, and human body temperature 3/8th up the scale.

So at their meeting in 1708, Fahrenheit learned of Romer’s temperature scale and adopted it as his own, adjusting it slightly because he found it “inconvenient and inelegant on account of the fractional numbers”. So he scaled them up to 8 and 24.

That is the original Fahrenheit scale. He produced thermometers for some time using this scale.

But then, at some later time Fahrenheit multiplied all numbers on his scale by four, setting freezing point to the now familiar 32 and body temperature to 96. It’s unclear exactly why he did this. He may just have wanted finer precision in his measurements but I think there was a better reason.

You see, Fahrenheit was an excellent instrument maker. His thermometers agreed with each other precisely, at a time when that was unheard of. He pioneered the use of mercury as a measuring liquid, which has the benefit of a much higher boiling point than the alcohol used in most other thermometers at the time. For these accomplishments, he was inducted into the British Royal Society.

And we know he read the works of Newton, Boyle, and Hooke, in which he would have come across the idea that a one degree increase in temperature should correspond to a specific fractional increase in the volume of the measuring liquid.

And today a one degree Fahrenheit increase in temperature increases the volume of mercury by exactly one part in 10,000. Is this just a coincidence? We’ll probably never know for sure because as an instrument maker Fahrenheit was secretive about his methods. But I think the data strongly suggests this was the case.

So what exactly did zero represent on the scales of Fahrenheit and Romer? By many accounts it’s the temperature of a salt, ice and water mixture. But there are different descriptions of these mixtures and none of them actually produces the temperature they’re supposed to. More likely I think they picked the coldest temperature in winter, set that as zero and later used ice and brine to calibrate new thermometers. Now his scale is only used regularly in the Cayman Islands, Bahamas, Belize, oh and the United States of America.

UV at ground level is non-ionizing but it damages DNA and causes photoaging - how?
Also, it turns out glass doesn't block all UV (specifically UVA passes through). This is something I learned filming with the UV camera inside.

Special thanks to Dr. Hayley Golbach, @hayleysgold on twitter
https://twitter.com/hayleysgold

Ultraviolet light causes damage to DNA, leads to cancer and photoaging: age spots and wrinkles. I was curious about this because UV is technically non-ionizing. A photon of UV doesn't have enough energy to strip an electron off atoms or molecules. However it does have enough energy to trigger photo-chemical reactions. For example, it causes pyrimidine dimers - the unauthorized covalent bonding of adjacent thymine or cytosine bases in our DNA. If these spots are not properly repaired, they may lead to mutations and cancer. Photoaging is typically the result of degradation of collagen and elastin fibers - scaffolding that supports the skin. This leads to wrinkles and saggy-looking skin.

Huge thanks to Patreon supporters:
Donal Botkin, Michael Krugman, Jeff Straathof, Zach Mueller, Ron Neal, Nathan Hansen, Yildiz Kabaran, Terrance Snow, Stan Presolski, James M Nicholson, KIMoFy

Support Veritasium on Patreon: http://ve42.co/patreon

Music from Epidemic Sound http://epidemicsound.com "Serene Story 2"

A planet has been predicted to orbit the sun with a period of 10,000 years, a mass 5x that of Earth on a highly elliptical and inclined orbit. What evidence supports the existence of such a strange object at the edge of our solar system?

Huge thanks to:
Prof. Konstantin Batygin, Caltech
Prof. David Jewitt, UCLA

I had heard about Planet 9 for a long time but I wondered what sort of evidence could support the bold claim: a planet at the very limits of our ability to detect one, so far out that its period is over 60 times that of Neptune. The planet 9 hypothesis helps explain clustering of orbits of distant Kuiper belt objects. It also explains how some of these objects have highly inclined orbits - up to 90 degrees relative to the plane of the solar system. Some are orbiting in reverse. Plus their orbits are removed from the orbit of Neptune, the logical option for a body that could have ejected them out so far. The fact that the perihelion is so far out suggests another source of gravity was essential for their peculiar orbits.

Special Thanks to Patreon Supporters:
Alfred Wallace, Arjun Chakroborty, Bryan Baker, Chris Vargas, Chuck Lauer Vose, DALE HORNE, Donal Botkin, Eric Velazquez, halyoav, James Knight, Jasper Xin, Joar Wandborg, Kevin Beavers, kkm, Leah Howard, Lyvann Ferrusca, Michael Krugman, Mohammed Al Sahaf, Noel Braganza, Pindex, Ron Neal, Sam Lutfi, Stan Presolski, Tige Thorman

Music from http://epidemicsound.com "Observations - From Now On" "Magnified XY"

Chaos theory means deterministic systems can be unpredictable. Thanks to LastPass for sponsoring this video. Click here to start using LastPass: https://ve42.co/VeLP
Animations by Prof. Robert Ghrist: https://ve42.co/Ghrist

Want to know more about chaos theory and non-linear dynamical systems? Check out: https://ve42.co/chaos-math

Butterfly footage courtesy of Phil Torres and The Jungle Diaries: https://ve42.co/monarch
Solar system, 3-body and printout animations by Jonny Hyman
Some animations made with Universe Sandbox: https://universesandbox.com/
Special thanks to Prof. Mason Porter at UCLA who I interviewed for this video.

I have long wanted to make a video about chaos, ever since reading James Gleick's fantastic book, Chaos. I hope this video gives an idea of phase space - a picture of dynamical systems in which each point completely represents the state of the system. For a pendulum, phase space is only 2-dimensional and you can get orbits (in the case of an undamped pendulum) or an inward spiral (in the case of a pendulum with friction). For the Lorenz equations we need three dimensions to show the phase space. The attractor you find for these equations is said to be strange and chaotic because there is no loop, only infinite curves that never intersect. This explains why the motion is so unpredictable - two different initial conditions that are very close together can end up arbitrarily far apart.

Music from https://epidemicsound.com "The Longest Rest" "A Sound Foundation" "Seaweed"

Spinning objects have strange instabilities known as The Dzhanibekov Effect or Tennis Racket Theorem - this video offers an intuitive explanation.
Part of this video was sponsored by LastPass, click here to find out more: https://ve42.co/LP

References:
Prof. Terry Tao's Math Overflow Explanation: https://ve42.co/Tao

The Twisting Tennis Racket
Ashbaugh, M.S., Chicone, C.C. & Cushman, R.H. J Dyn Diff Equat (1991) 3: 67. https://doi.org/10.1007/BF01049489

Janibekov’s effect and the laws of mechanics
Petrov, A.G. & Volodin, S.E. Dokl. Phys. (2013) 58: 349. https://doi.org/10.1134/S1028335813080041

Tumbling Asteroids
Prave et al. https://doi.org/10.1016/j.icarus.2004.07.021

The Exact Computation of the Free Rigid Body Motion and Its Use in Splitting Methods
SIAM J. Sci. Comput., 30(4), 2084–2112
E. Celledoni, F. Fassò, N. Säfström, and A. Zanna
https://doi.org/10.1137/070704393

Animations by Iván Tello and Isaac Frame

Special thanks to people who discussed this video with me:
Astronaut Don Pettit
Henry Reich of MinutePhysics
Grant Sanderson of 3blue1brown
Vert Dider (Russian YouTube channel)

Below is a further discussion by Henry Reich that I think helps summarize why axes 1 and 3 are generally stable while axis 2 is not:

In general, you might imagine that because the object can rotate in a bunch of different directions, the components of energy and momentum could be free to change while keeping the total momentum constant.

However, in the case of axis 1, the kinetic energy is the highest possible for a given angular momentum, and in the case of axis 3, the kinetic energy is the lowest possible for a given angular momentum (which can be easily shown from conservation of energy and momentum equations, and is also fairly intuitive from the fact that kinetic energy is proportional to velocity squared, while momentum is proportional to velocity - so in the case of axis 1, the smaller masses will have to be spinning faster for a given momentum, and will thus have more energy, and vice versa for axis 3 where all the masses are spinning: the energy will be lowest). In fact, this is a strict inequality - if the energy is highest possible, there are no other possible combinations of momenta other than L2=L3=0, and vice versa for if the energy is the lowest possible.

Because of this, in the case of axis 1 the energy is so high that there simply aren't any other possible combinations of angular momentum components L1, L2 and L3 - the object would have to lose energy in order to spin differently. And in the case of axis 3, the energy is so low that there likewise is no way for the object to be rotating other than purely around axis 3 - it would have to gain energy. However, there's no such constraint for axis 2, since the energy is somewhere in between the min and max possible. This, together with the centrifugal effects, means that the components of momentum DO change.

This is what a nuclear disaster area looks like.
Check out Audible: http://bit.ly/AudibleVe
Broadcast locations and times:

North America: PBS, July 28 & 29 @ 10pm ET / 9pm Central
Europe: ZDF/arte, July 31 @ 10pm
Australia: SBS, August 6, 13, 20 @ 8:30pm EST

Not broadcast in your country? Contact your local broadcaster and/or email www.genepoolproductions.com

Music by Kevin Macleod http://incompetech.com 'Come Play With Me' & 'Lost Frontier'

Well an atom's made of protons, neutrons, and electrons
the first two in the nucleus, the third around it
it's mostly empty space, but it feels solid in any case

The elements are all the different types of atoms
they differ by the number of protons in the middle.
Hydrogen has only one, but Uranium has a ton

It's just chemistry that you and me are made of these atoms

Well atoms bond together to form molecules
Most of what's surrounding me and you
Water, sugar, things yet undreamed of of of of

Look around you, see the combinations in a eucalypt tree
Mendeleev's periodicity
gives us sand and water and the air above ove ove ove ove

It's just chemistry that you and me are made of these atoms:
Hydrogen, Oxygen, Carbon, Nitrogen, make up the world's life forms

Do do do you, do do do do
but do you wonder how
matter forms something strange
when there's a chemical change?

Where did these atoms come from? They were fused in stars
Light elements combine releasing light from afar
Fusion in the sun, creates Helium

I guess what I be saying is you gotta use your reason
To open up your mind and see the cause of the seasons
-How do we know what's true? The scientific method shows you

It's just chemistry that you and me are made of these atoms

Atoms bond together to form molecules
Most of what's surrounding me and you
Water, sugar, sand and you'll find things undreamed of

So Argon, Neon, Xenon
There's no need to overstate
'Cause we are of course
This, of this, of this, we're made: atoms

Can you solve these four rotation-related riddles?
Support Veritasium on Patreon: http://ve42.co/patreon
Test yourself playlist: http://ve42.co/testurself

Huge thanks to Patreon supporters:
Jeff Straathof, Zach Mueller, Ron Neal, Nathan Hansen

I came across these four physics puzzles over the years in discussions with Neil deGrasse Tyson (riddle 4: which part(s) of a moving train are going backwards with respect to the ground?), Simon Pampena (riddle 2: run around a track twice, the first time slowly, the second time much faster so that the average for the two laps is twice the speed of the first lap). Someone tweeted me a video of the mystery cylinder rolling down the ramp in riddle 1 (sorry I'm not sure who it was). Riddle three about a bicycle going forward or backward when it's bottom peddle is pulled back was brought to me by a number of people and I appreciate all of their help!

Filmed by Raquel Nuno.
Thanks to everyone at the Palais de la Decouverte! I've had this footage for five years and am only finally releasing it now. I wanted to talk about the way grass grows on a spinning turntable but I couldn't locate the footage...

How Schlieren imaging works in color, black and white and slow-mo.
Get a free audiobook with a 30 day free trial at http://www.audible.com/veritasium

Special thanks to Patreon supporters:
Tony Fadell, Donal Botkin, Curational, Jeff Straathof, Zach Mueller, Ron Neal, Nathan Hansen, Corvi

Support Veritasium on Patreon: http://ve42.co/patreon

Filming by Raquel Nuno
Sound Effects by A Shell in the Pit

Thank you to Rodney Fox for sharing his story. He was attacked by a shark 50 years ago - Dec. 8 1963. If you're interested in his book or in going shark cage diving in South Australia, check out: http://bit.ly/rodneyfox

The story of three impressive high school science projects. Can you guess which student won $250,000 in the #RegeneronSTS? Applications open June 1: http://bit.ly/2HkLXT1 This video was sponsored by Regeneron. The Science Talent Search was founded and produced by the Society for Science and the Public.

Huge thanks to the students: Ronak Roy, Ana Humphrey, and Anjali Chadha. It was great getting to meet all of you and learn about your original scientific research.

Special thanks to Assistant Professor Konstantin Batygin for discussing Ana's research and Planet 9 with me. More is coming on the Planet 9 front.

Ronak came up with a new design for the phoropter, the device used to determine eye-glass prescriptions. It's basically been unchanged for 200 years. Using a liquid lens, he miniaturized the device and wrote an algorithm to determine your prescription.

Ana used math and physics to search for hidden exoplanets. There are a number of reasons why the transit method and Kepler telescope may have missed them: they're too small, too inclined, or take too long to orbit and so were not seen. By considering which planetary systems have additional space for more planets, Ana came up with 560 locations where we may look again for planets in future.

Anjali developed an internet enabled device for measuring arsenic concentrations in drinking water. The device performs several chemical reactions to release the arsenic into a measurable state. It then reacts the arsenic with a test strip to produce a color output. This color is sampled by a camera and processed to determine the concentration of arsenic in the water sample. This has significant potential applications around the world helping reduce exposure to arsenic and potentially other contaminants.

Filming by Raquel Nuno

If you spin a raw egg and then stop it, it will start spinning again without you having to touch it. A boiled egg, on the other hand, stops and stays stopped. Why is this? Well a raw egg contains a yolk that moves inside the egg independently of the shell. If you stop the shell, the yolk inside continues to move due to its inertia and it therefore gets the egg spinning again.

I took a boat through 96 million black plastic balls on the Los Angeles reservoir to find out why they're there. The first time I heard about shade balls the claim was they reduce evaporation. But it turns out this isn't the reason they were introduced.

Huge thanks to LADWP for arranging this special tour for me. Next time let's put the GoPro on the submersible!

The balls are made of high density polyethylene (HDPE) which is less dense than water so they float on the surface of the reservoir even if they break apart. They are 10cm (4 inches) in diameter and contain about 210ml of water. So the main reason they are on the reservoir is to block sunlight from entering the water and triggering a chemical reaction that turns harmless bromide into carcinogenic bromate. This effect occurs with prolonged exposure to bromate so regulators insist that levels be kept below 10 microgram per liter on average over a 12 month period.

Special thanks to Patreon supporters:
Donal Botkin, Michael Krugman, Ron Neal, Stan Presolski, Terrance Shepherd, Penward Rhyme and everyone who provided feedback on an early draft of this video.

Thanks to:
Las Virgenes Reservoir for footage of initial shade ball dump
Euro-Matic for bird into jet-engine footage

Researched and Produced by Casey Rentz

Animations by Maria Raykova

Music from http://epidemicsound.com "Colorful Animation 4" "Seaweed"

And from Kevin MacLeod "Marty Gots a Plan"

This is an educational video about the science of water quality.

Scientists have combined ultrasound, viruses and synthetic drugs to control regions of the brain.
Check out Skillshare: https://skl.sh/veritasium (first 500 get 2 months free)

Special thanks to Prof. Mikhail Shapiro and Dr. Jerzy Szablowski:
http://shapirolab.caltech.edu

Human brains are complicated - the most complicated thing in the known universe, many people say. So far we understand little - just that certain regions of the brain appear to be involved in certain activities and certain disorders. In extreme cases this has led to the practice of removing sections of the brain, or using electrodes or optical fibers to control activation rates. What is unique about this approach is it offers a way to turn on and off specific brain regions without invasive surgery. It has promise because it combines existing technologies: micro-bubbles, ultrasound, synthetic viruses, and synthetic drugs to achieve this goal.

Special thanks to Patreon supporters:
Donal Botkin, James M Nicholson, Michael Krugman, Nathan Hansen, Ron Neal, Stan Presolski, Terrance Shepherd

Animations and editing by Alan Chamberlain

Music from http://epidemicsound.com "Experimental1"

Mosquitoes are attracted to me and it's likely due to my genes.
This video is sponsored by 23andMe https://23andme.com/veritasium
Huge thanks to Prof. Immo Hansen and team: http://ve42.co/hansen

References:
Genome Wide Association Study for self-reported mosquito attractiveness:
http://ve42.co/MossieGWAS

The twin study showing correlated attractiveness is stronger for identical twins:
http://ve42.co/MossieTwins

Some things we know make mosquitoes more attracted to you:
Exercising, higher metabolism, higher body temperature, more body odor, being pregnant, type O blood, infrequent bathing, lactic acid, ammonia, acetone.

There are a number of folk remedies people believe protect them from mosquito bites like drinking alcohol, eating garlic, or taking vitamin B. These do not appear to provide any benefit in lab studies and in fact drinking alcohol is associated with increased mosquito activity because it causes blood vessels near the surface of the skin to dilate.

And apparently some of your attractiveness to mosquitos is simply genetic. This may be mediated through your immune system, which is what a lot of the genes identified were associated with.

Molecular models are microSnatoms: http://snatoms.com

Filming in New Mexico by Raquel Nuno
Animations by Jacqui Robertson

The opinions and conclusions drawn in this video are those of Veritasium and not 23andMe.

In Queenstown, New Zealand, I jumped off the Kawarau Bridge - the site of the first bungy jump. It was a thrilling experience, preceded by a terrifying, gut-wrenching half hour wait. All in all an awesome adventure, even if the woman fitting my harness didn't know the first thing about the acceleration of free-falling bodies.

Smarter Every Day Collaboration video: http://youtu.be/riwc3UgPaHw
The Veritasium treatment of the final transit of Venus this century. The weather behaved for some key moments allowing me to observe Venus passing across the disk of the sun. The transit of Venus is steeped in historical significance. Observations of the transit in 1769 led to the first really accurate calculation of the Earth-Sun distance (or one astronomical unit AU). Since Cook was in Tahiti he then mapped the East coast of Australia and parts of New Zealand.

When is the acceleration (rate of speeding up or slowing down) greatest during a bungy jump?

How should we depict an atom? Like a solar system with electrons orbiting the nucleus on hula hoop orbits? That idea is so last century! Bosi takes us into the quantum world, where an electron's position and velocity aren't well defined - all we can calculate are the probabilities e.g. of finding an electron at different points in space. When we do that, we find electrons do not neccessarily occupy circles or spheres in space. Rather their probability densities make all sorts of interesting shapes from the dumbell to the peanut with the donut around it.

At the jumper's fastest point, the acceleration is by definition zero. That is because the jumper is going from speeding up to slowing down. At this instant then there is no change in the jumper's velocity. This is counter-intuitive for a lot of people because it's easy to confuse velocity with acceleration. Velocity is how fast something goes while acceleration is the rate at which velocity changes.