What is radiation? Are all types harmful? What are the most common sources of damaging radiation? Most people view radiation as harmful and negative without understanding what makes it potentially damaging and which forms should be avoided. For example, many felt radiation from mobile phones probably caused cancer but few focused on the carcinogenic effects of UV rays.

Research has found some human brains can pick up on rotations of geomagnetic-strength fields as evidenced by drops in alpha wave power following stimulus. For more, see https://ve42.co/magneto

Huge thanks to:
Prof. Shinsuke Shimojo, Connie Wang, and Isaac Hilburn, plus Prof. Joe Kirschvink. Their lab: https://ve42.co/maglab

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

Additional filming by Whitney Clavin

A story is worth a thousand data points.
My second channel: http://bit.ly/2veritasium
More info on this topic: http://wke.lt/w/s/TzNC0

There are a few persistent misconceptions about what causes the seasons. Most believe it is the distance between the Earth and sun which varies to give us seasonal temperature variations. However it is actually the directness of the sun's rays leading to more intense sunshine in summer and less in winter.

A basketball and a 5kg medicine ball are dropped simultaneously. Which one hits the ground first? It seems obvious that the heavy one should accelerate at a greater rate and therefore land first because the force pulling it down is greater. But this is forgetting inertia - the tendency of mass to resist changes in motion. Therefore, although the force on the medicine ball is greater, it takes this larger force to accelerate the ball at the same rate as the basketball.

Without neutrons, harnessing nuclear energy would be impossible.
Try Audible free for 30 days: http://audible.com/veritasium

I have a new documentary coming out in a few months - sign up here to be notified and see a sneak preview: http://vitamaniathemovie.com

Special thanks to Patreon supporters:
Tony Fadell, Donal Botkin, Michael Krugman, Jeff Straathof, Zach Mueller, Ron Neal, Nathan Hansen, Yildiz Kabaran,
Terrance Snow

A few years ago I made a documentary about uranium, radioactivity and radiation. I always thought of the characters in our story as the scientists and maybe the uranium nucleus itself. It was only through making the documentary that I realized the real hero of the story is the neutron. Without a neutral nuclear particle, it would be virtually impossible to release the energy from the nucleus. But with it, and the idea of a chain reaction, nuclear energy went from science fiction to reality. That is something I had not grasped as clearly before and it motivated me to make this video.

Filmed by Raquel Nuno.

JJ Thomson proposed the first model of the atom with subatomic structure. He had performed a series of experiments and was credited with the discovery of the first sub-atomic particle, the electron. He therefore proposed a new model of the atom called the plum pudding model. In this model, the plums represent negatively charged electrons which can be plucked out of the atom, leaving behind some positively charged pudding. In this film, cherry tart is used as a delicious substitute for plum pudding.

Countries are powered by a diverse range of energy sources, but in Australia electricity generation mainly has one source: fossil fuels. Coal, natural gas, and oil account for over 90% of the country's electricity. Hydro provides 7% with only 0.3% provided by wind and solar. Should Australia consider nuclear power? It is a complicated issue leaving many uncertain about its place in Australia's energy future.

In 2020, NASA will send a new rover to the Martian surface with one of its objectives to search for evidence of ancient life on the planet. I made this clip as a correspondent for Bill Nye Saves the World on Netflix.

Touring the Jet Propulsion Lab (JPL) in Pasadena was an awesome experience. I didn't think we were going to get into the control room but we got lucky. Some of the greatest moments in the history of space exploration have taken place there. They have a giant vacuum chamber where they can take the rover down to the atmospheric pressure on Mars (roughly .01x Earth's atmosphere) and test all of the devices to make sure there are no electrical discharges due to the reduced pressure. I also enjoyed seeing how the rocks will be cored and stored in tubes and deposited on the Martian surface awaiting pickup by the following mission.

Images courtesy of NASA.

Filmed by Raquel Nuno from 3:30 onwards.

Music: http://epidemicsound.com "Serene Story 2"

Sound waves in a tube of gas create flames of different heights that dance to the music. A metal tube with holes in it is filled with gas. The gas is lit to create a row of tiny flames. A speaker at one end plays sound into the tube, which creates a standing wave of sound: areas where air molecules are vibrating rapidly separated by areas where the air is fairly still. This produces the different heights of flames and allows the wavelength of the sound wave to be estimated.

Droplets levitate on a bath of liquid nitrogen and are spontaneously self-propelled. Thanks Audible! Start a 30-day trial and your first audiobook is free. Go to https://audible.com/VERITASIUM or text VERITASIUM to 500500.

Special thanks to Dr. Anaïs Gauthier
Physics of Fluids: https://pof.tnw.utwente.nl/

Self-propulsion of inverse Leidenfrost drops on a cryogenic bath
Anaïs Gauthier, Christian Diddens, Rémi Proville, Detlef Lohse, and Devaraj van der Meer
PNAS January 22, 2019 116 (4) 1174-1179; published ahead of print January 22, 2019
https://www.pnas.org/content/116/4/1174

For a detailed description of the setup:
http://www.lps.ens.fr/~adda/pa....piers/Langmuir2016.p

And self-propulsion is also seen: http://www.lps.ens.fr/~adda/pa....piers/InvLeidenfrost

Other recent (hot) Leidenfrost experiments that might be interesting:
* Leidenfrost wheels: https://www.youtube.com/watch?v=glRGl-eYuXo
* Leidenfrost maze: https://www.youtube.com/watch?time_continue=174&v=vPZ7sx3EwUY
* Leidenfrost explosions: https://www.youtube.com/watch?v=z0sp3AjgUy4

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

Thanks to Prof. Kevin McKeegan at UCLA for the liquid nitrogen

Filming by Raquel Nuno

Additional animations by Alan Chamberlain

What happens when a super long slinky is dropped?

I have the photic sneeze reflex so I sneeze when I look at bright light.
Check out 23andMe: http://ve42.co/23andme
*So technically the single nucleotide swap (C instead of T) is not actually in a gene per se but in an intergenic region on chromosome 2. It's also not clear exactly how this affects physiology or causes the sun sneeze but there is correlative evidence that every copy of this single nucleotide polymorphism (SNP) is associated with a 1.3x increase in likelihood of having the photic sneeze reflex.

I have wanted to make a video about sun-sneezing for a long time. It is something I've experienced my whole life. When I go from a dark room indoors into full sunlight I invariably sneeze. I thought everyone did it. So my original question was why do people sneeze when they see bright light? That led me to consider what possible evolutionary advantages there could be to sneezing in sunlight. The obvious advantage to me is that sunlight kills pathogens of which there may be many in your snot or mucus. So sneezing in sunshine is a much better idea than sneezing inside a dark, damp cave where you may be living.

For more info, check out:
Web-Based, Participant-Driven Studies Yield Novel Genetic Associations for Common Traits
http://journals.plos.org/plosg....enetics/article?id=1

Filmed by Raquel Nuno

How can you Yo-Yo without the string attached?
Check out Audible: http://bit.ly/AudibleVe
For more Ben Conde: http://bit.ly/VeBenConde
For Beyond Slow Motion: http://bit.ly/VeBeyondSlowMo

For more on yo-yos check out: http://bit.ly/290wR3a

How to yo-yo without a string attached... So many crazy tricks and the science that makes it possible.

Edited and animated by Daniel Joseph Files

Veritasium second channel: http://bit.ly/2Veritasium
Rodney Fox Shark Attack Story: http://bit.ly/1frAwlI
Check out Audible: http://bit.ly/AudibleVe

For this video I went off the coast of South Australia to an island frequented by great white sharks. Here they hunt seals and fish. I've never been scuba diving before but I got into a cage and filmed the sharks under water. It was an incredible experience. Then we came back on the surface to tag the sharks.

Newton's Law of Universal Gravitation can be summarized as "all mass attracts all other mass." But if this is true, why don't we notice the gravitational force of attraction between everyday objects? The reason is because the gravitational force is quite weak.

We talk about all the potentially challenging situations autonomous cars could get into but not about how human drivers are not very good. Tens of thousands die on the roads every year in collisions, most of which could be prevented by autonomous vehicles.
Sponsored by BMW

I wanted to make a video about autonomous cars for some time but I hadn't had the opportunity. The self-driving technology is already at a state where it can save lives if only it were more widely implemented.

Links to original clips:
TED-Ed https://www.youtube.com/watch?v=ixIoDYVfKA0
BBC Newsnight: https://www.youtube.com/watch?v=FypPSJfCRFk&t=172s

Music from http://www.epidemicsound.com "Ambient Electronic Groove," "Pet Animals 2," "The Long Ride."
Filmed by Raquel Nuno
Edited by Trevor Carlee

In April 2012, I was part of a team of scientists, teachers and students who travelled to Alaska to observe the Northern Lights or Aurora Borealis. Our mission was a unique one - to launch weather balloons up to 100,000 feet loaded with experiments, tracking devices and HD cameras. This is the result of our trip, produced for Catalyst on ABC1 http://www.abc.net.au/catalyst/

Everything is not as it first appears. This simple plastic ball looks purple until you swing it in a circle and reveal its true nature. Inside are three light emitting diodes (LEDs), which are red, green and blue. They turn on and off in sequence very quickly. When still, the ball appears purple because your eyes and brain don't 'refresh' quickly enough to perceive the changing colours. However, when swung in a circle, the ball changes colours at different locations so the colours don't merge with each other and the ball's true nature is revealed. Now let's not think too carefully about how this illusion is conveyed through video (because the camera doesn't refresh quickly enough to perceive the colours changing either - so you have no hope of seeing it on YouTube even frame by frame).

My hypothesis is that the algorithm, rather than viewer preference, drives views on the site. As the algorithm shifts, various YouTubers experience burnout (as what used to work no longer works) and right now click-through rate is the key metric. So clickable titles and thumbnails are the only way to get a lot of impressions and hence views - they are the only way to go viral. This leads me to wonder which audiences will become most prevalent on the site and if there will even be a place for educational content. In the long-term, hopefully YouTube is able to measure satisfaction through surveys and other metrics to ensure an optimal experience for everyone on the site.

Flipchart artwork by Maria Raykova
Filmed by Raquel Nuno
Thumbnail by Ignat Berbeci