In 2018 the kg will be defined by Planck's constant, not a hunk of metal.
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Special thanks to the staff at NIST who made this possible: Darine Haddad, Jon Pratt, Stephan Schlamminger, and Ben Stein.

Additional footage and animations by Sean Kelley, Jennifer Lauren Lee, and Frank Seifert.

I have been obsessed with measurement for a long time and I'm not sure quite how it happened. The world's roundest object played a role in this. I guess I'm just fascinated by how difficult it is to pin down a quantity like a kilogram. A physical object seemed like a good idea until the mass of the international prototype kilogram wasn't as constant as expected. These methods of the Kibble balance and silicon sphere have shown better precision than 20 parts per billion, making them superior to the old method. The agreement between Avogadro approaches

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

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

Interferometer video by TSG Physics: https://www.youtube.com/watch?v=j-u3IEgcTiQ

Music from http://epidemicsound.com "ExperiMental1" by Gunnar Johnsén

Studio filming by Raquel Nuno

Uranium is a unique element, used in research, medicine, space travel, and of course weapons.
Not broadcast in your country? Contact your local broadcaster and/or email www.genepoolproductions.com

Documentary Dates:
US: PBS, July 28 & 29 @ 10pm ET / 9pm Central
France & Germany: ZDF/arte July 31 @ 10pm
Australia: SBS, August 6, 13, 20 @ 8:30pm EST

If you're wondering where the title comes from...
“A number of ingenious experiments were devised to test the speed of the fission reaction, and the limit was pushed. But even so, I thought it would be very nice to go one step nearer to a real atomic explosion. Dick Feynman, who was present, started to chuckle and to say that this is just like tickling the tail of a sleeping dragon.”
Professor Otto R Frisch, January 1969 Physicist, the Manhattan Project.

Celsius never devised nor used the scale that now bears his name.

Veritasium is now on Patreon: http://patreon.com/veritasium

Special thanks to Michael Stevens of Vsauce! http://youtube.com/vsauce1

More info about Celsius and temperature scales: http://wke.lt/w/s/2I6Nu

References for this video:

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

Special Thanks to the Uppsala University Museum
I filmed this in Uppsala in the summer of 2012! So I've been thinking about this idea for a very long time. I'm glad to finally have it out there in the world.

Explanation of gyro precession: http://bit.ly/U4e8HQ
More: http://bit.ly/GyroMORE
Less Than: http://bit.ly/GyroLESS
Equal To: http://bit.ly/GyroEQUAL

Huge thanks to A/Prof Emeritus Rod Cross, Helen Georgiou for filming, Alex Yeung, and Chris Stewart, the University of Sydney Mechanical Engineering shop, Duncan and co. Ralph and the School of Physics.

In this video I attempt to lift a 19kg (42 lbs) wheel over my head one-handed while it's spinning at a few thousand RPM. This replicates an earlier experiment by Professor Eric Laithwaite. He claimed the wheel was 'light as a feather' and could not be explained by Newton's Laws. I wanted to find out for myself what I really felt like.

Music By Kevin MacLeod www.Incompetech.com "Tempting Secrets"

Boredom makes you more creative, altruistic, introspective, and helps with autobiographical planning.
This video was sponsored by LastPass: http://bit.ly/2wAsdUu

I feel like this video might come across as condescending but the person I'm really talking to is myself. Despite the fact that I know how useful it can be to be bored, I still find myself trying to fill every last moment with stimulus. Boredom is unpleasant - the open, unstructured thinking that can take place can also feel pointless. But now I'm made this video to remind myself how important boredom is so hopefully I'll make more time to be bored.

More resources:

The boredom leads people to shock themselves study:
Just Think: The challenges of the disengaged mind
https://wjh-www.harvard.edu/~d....tg/WILSON%20ET%20AL%

Boredom leads people to consider their future and set goals study:
Back to the future: Autobiographical planning and the functionality of mind-wandering
https://www.sciencedirect.com/....science/article/pii/

On boredom and altruism:
https://pdfs.semanticscholar.o....rg/ca72/0f959d3c9c31

Does boredom make us more creative?
https://www.tandfonline.com/do....i/abs/10.1080/104004

Amazing filming by Raquel Nuno

Music from http://epidemicsound.com "I Think I Was There" "Critical Thinking 2" "Wide Open" "Seaweed" "A Sound Foundation 1"

Music also by Kevin MacLeod http://incompetech.com "Fig Leaf Rag"

Why do droplets of food coloring attract, repel, and chase each other?
Snatoms molecular models: http://igg.me/at/snatoms
More about this topic: http://wke.lt/w/s/VRjRQ

Original paper on droplets: http://stanford.edu/~manup/doc....s/Cira_DancingDrople
Marangoni Flow: http://web.mit.edu/2.21/www/Le....c-notes/Surfacetensi
Surface Energy: https://itf.fys.kuleuven.be/~j....oi/papers/Wetting%20

Filming and master pipetting by Raquel Nuno
Research and writing by Aaron White

Why does shaken soda explode? Does ice melt first in fresh or salt water?
Thank you Squarespace for sponsoring this video. Go to https://squarespace.com to save 10% off your first purchase of a website or domain using code: VERITASIUM

This video features experiments that have been shown to me by science teachers over the years. Does ice melt fast in salt water or fresh water was an experiment introduced to me at the Utah Science Teachers' conference. The ring of metal over a chain demo came from a teachers event in Florida. The idea shaking a carbonated drink increases pressure came from an email.

Special thanks to Petr Lebedev for building the pressure gauge.

Links to literature are below:
Victims of the pop bottle, by Ted Willhoft. New Scientist, 21 August 1986 p.28

Carbonation speculation
The Physics Teacher 30, 173 (1992); https://doi.org/10.1119/1.2343501

Agitation solution
The Physics Teacher 30, 325 (1992); https://doi.org/10.1119/1.2343556

Filmed by Cristian Carretero, Jordan Schnabel, Jonny Hyman, and Raquel Nuno

Music from https://epidemicsound.com "Seaweed" "Quietly Tense" "Mind Shift" "Observations"

In space, metals can weld together without heat or melting.
Check out Audible: http://bit.ly/AudibleVe
Support Veritasium on Patreon: http://bit.ly/VePatreon

Written by Joh Howes and Derek Muller

Yes, it's pronounced Gemini (ee not eye) because that's the way everyone pronounced this mission.

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

References:
Gemini IV transcripts: http://www.jsc.nasa.gov/histor....y/mission_trans/gemi

Gemini IV recordings:
https://archive.org/details/Gemini4 (relevant clip is 1297 at about 2:00)

ESA cold welding recommendations:
esmat.esa.int/Publications/Published_papers/STM-279.pdf

Cold welding gold nanowire:
http://www.nature.com/nnano/jo....urnal/v5/n3/full/nna

Music by Kevin MacLeod "Intrepid" http://www.incompetech.com

Many technologies have promised to revolutionize education, but so far none has. With that in mind, what could revolutionize education?
These ideas have been percolating since I wrote my PhD in physics education: http://www.physics.usyd.edu.au..../super/theses/PhD(Mu
I have also discussed this topic with CGP Grey, whose view of the future of education differs significantly from mine: https://www.youtube.com/watch?v=7vsCAM17O-M

I think it is instructive that each new technology has appeared to be so transformative. You can imagine, for example, that motion pictures must have seemed like a revolutionary learning technology. After all they did revolutionize entertainment, yet failed to make significant inroads into the classroom. TV and video seem like a cheaper, scaled back film, but they too failed to live up to expectations. Now there is a glut of information and video on the internet so should we expect it to revolutionize education?

My view is that it won't, for two reasons: 1. Technology is not inherently superior, animations over static graphics, videoed presentations over live lectures etc. and 2. Learning is inherently a social activity, motivated and encouraged by interactions with others.

Filmed and edited by Pierce Cook

Supported by Screen Australia's Skip Ahead program.

Music By Kevin MacLeod, www.incompetech.com "The Builder" and by Amarante Music: http://www.amarantemusic.com

How the brain works, how we learn, and why we sometimes make stupid mistakes.
Submit ideas: http://ve42.co/GotIdeas
Apply to work with me: http://ve42.co/JoinUs

Thanks to Patreon supporters:
Nathan Hansen, Donal Botkin, Tony Fadell, Zach Mueller, Ron Neal

Support Veritasium on Patreon: http://bit.ly/VePatreon

This video was inspired by the book Thinking Fast and Slow by Daniel Kahneman

Harpist: Lara Somogyi http://ve42.co/Lara
Animator: Jesse Agar http://ve42.co/ThisPlace
Filmed by Raquel Nuno

Music by Kevin MacLeod, http://incompetech.com "Sneaky Adventure" "Harlequin"

This is how a slinky falls in slow motion - it appears to defy gravity but the centre of mass is accelerating at 9.8m/s^2 meaning the top is accelerating faster than that and the bottom is not falling at all until the entire slinky collapses.

Read a pre-print of the physics paper here: http://arxiv.org/abs/1208.4629
Music by Kevin McLeod http://incompetech.com
Songs: Industrial Music Box, Heavy Interlude, Pale Rider, Decisions.

Slow motion photography courtesy of Questacon http://questacon.edu.au

The original goal of Veritasium was to show the beauty of science and I think the first minute and a half of this is the closest I've come. This is the last in a series of six videos about slinkies.

When a tube spins with an X and an O labelled at either end, why do we see only one letter during the rotation?

Higher: http://bit.ly/blockhigher
Same height: http://bit.ly/SameHeight
Lower: http://bit.ly/BlockLower

Special Thanks to:
Henry (MinutePhysics): http://www.youtube.com/minutephysics
Destin (Smarter Every Day): http://www.youtube.com/smartereveryday
Greg and Mitch (ASAP Science): http://youtube.com/asapscience
Elise Andrew (I F***ing Love Science): http://youtube.com/iflscience

Thanks to everyone at RIT and Dickinson College who helped with the making of this video:
Rochester Institute of Technology
Robert Teese, Katelyn Wilkerson, Andrew Gillie, Andrew Stidwill

Dickinson College
This experiment was the brainchild of David Jackson based on a demo at Princeton.
Priscilla Laws, Catrina Hamilton-Drager, Maxine Willis

High-speed camera support:
Charles Zwemer and Bria Antoine

Do negative air ions improve mood, anxiety, depression, alertness?
Part of this video was sponsored by LastPass, click here to find out more: http://bit.ly/2RZZTZk

Special thanks to Prof. Jack Beauchamp and Dr. Nathan Dalleska from Caltech for all their help running these experiments and discussing the research. For more, check out the links below:
http://www.cce.caltech.edu/peo....ple/jesse-l-jack-bea
http://beckmaninstitute.caltech.edu/eac.shtml

If you want to dig into the research on negative ions yourself, I suggest starting with the review studies:

Air ions and mood outcomes: a review and meta-analysis.
Perez V, Alexander DD, Bailey WH.
BMC Psychiatry. 2013 Jan 15;13:29.
https://www.ncbi.nlm.nih.gov/pubmed/23320516

Air ions and respiratory function outcomes: a comprehensive review
Dominik D Alexander, William H Bailey, Vanessa Perez, Meghan E Mitchell, and Steave Su
J Negat Results Biomed. 2013; 12: 14.
https://www.ncbi.nlm.nih.gov/p....mc/articles/PMC38485

Exposure of laboratory animals to small air ions: a systematic review of biological and behavioral studies.
Bailey WH, Williams AL, Leonhard MJ.
Biomed Eng Online. 2018 Jun 5; 17(1):72.
https://www.ncbi.nlm.nih.gov/pubmed/29866122

Thumbnail photography by Raquel Nuno

VFX by Alan Chamberlain

Sound recording by Whitney Clavin

Motion Graphics by Charlie Kilman

Music from Epidemic Sound: http://epidemicsound.com "Capture a Picture 1" and "Seaweed"

The nutrient content of food is declining. Is it because of soil depletion, selective breeding, or... something else?
Watch my new documentary, VITAMANIA: http://ve42.co/vita

I came across this story as I was making the film Vitamania. When you ask sellers of vitamins why you should take vitamin supplements even if you eat a healthy diet, they will say because our food doesn't contain all the nutrients it once did. This is supposedly due to soil depletion, cold storage, food ripening off the vine, and global transport of out-of-season foods. And to an extent this is true. Foods contain the greatest amount of nutrients if they are eaten soon after they are harvested. An unexpected source of nutrient decline is the increasing amount of carbon dioxide in the atmosphere. It causes plants to grow faster and bulk up on carbs but at the expense of other nutrients, so in percentage terms the amount of nutrients are actually declining. For now this decline is modest so supplementing with vitamin pills is probably unnecessary for most people with a healthy diet but it may be a concern in future.

Thanks to Kate Pappas & Chris Kamen for writing, producing and filming this video with me
Edited by Lucy McCallum
Sound mix by Wayne Hyett
Fact Checking by Calvin Lee and Claire Smith
Thanks to the Collingwood Children’s Farm and Glenn Fitzgerald from the University of Melbourne & Agriculture Victoria

Further Reading:

https://www.sciencedirect.com/....science/article/pii/
https://www.ncbi.nlm.nih.gov/p....ubmed/15637215/?ncbi
http://soils.wisc.edu/facstaff..../barak/poster_galler
https://www.politico.com/agend....a/story/2017/09/13/f
http://www.abc.net.au/news/201....8-05-24/scientists-w

For a report on ABC's Catalyst program (http://www.abc.net.au/catalyst/), I visited the Large Hadron Collider in Switzerland to find out what is being done now that the Higgs Boson has been discovered.

Although its mass has been measured around 125-126 GeV most of the other properties of the particle remain unknown. Its spin appears to be 0 or 2 but more results are required to nail this down. If it is the standard model Higgs, the spin should be 0, resulting in a fairly symmetric distribution of decay products in the detectors.

We may know this year if it's not the standard model Higgs - this would be the case if it doesn't decay into specific particles with the expected frequency. However if it is the standard model Higgs, it may take many more years to be certain. The large hadron collider will be shut down in 2013 for upgrades so that higher energies up to 14 TeV can be tested. Right now the LHC is operating at 8 TeV. The next announcement is expected in December.

What is the specious present? And how do our brains perceive time?
Get a 30-day free trial on Audible: http://bit.ly/AudibleVe
More info about this topic: http://wke.lt/w/s/z8TeR

A rare look inside the Svalbard Global Seed Vault which is closed ~350 days a year
Check out Audible: http://bit.ly/AudibleVe
More info on the seed vault: http://wke.lt/w/s/EKFlK
My trip to Norway was funded by Screen Australia, Film Victoria and Genepool Productions as part of a new project. More information soon.

Special thanks to Bente Naeverdal and the Crop Trust: https://www.croptrust.org

In a zero-g plane I experimented with flames and slinkies with surprising results.
Check out e-penser's video: http://ve42.co/EPzeroG
Check out Physicsgirl's video: http://ve42.co/PGzeroG

Thanks to Novespace: http://ve42.co/novespace

Special thanks to Patreon Supporters:
Tony Fadell, Donal Botkin, Nick Luchsinger, Jeff Straathof, Zach Mueller, Ron Neal, Nathan Hansen

The zero-g plane allows for a lot of experiments to be conducted without the expense of getting equipment into orbit. Apparently 80% of microgravity research can be performed in a zero-gravity plane, which is much cheaper than going to space. The flame from the lighter seemed much lazier in zero-g because without weight there is no buoyant force and therefore no convection. This makes the process of combustion more challenging because it's difficult for oxygen to reach the fuel.

Music from the Epidemic Sound: http://ve42.co/epidemic
"Serene Story 2" "In Orbit 2"

SEE THE SETUP FIRST: http://bit.ly/bulletblock
Click here for the explanation: http://bit.ly/1dHPk2K
Spinning Tube: http://bit.ly/Va43Z6
Spinning Disk: http://bit.ly/14MSKsT
Chain Drop: http://bit.ly/1713VQO
Spool: http://bit.ly/14wkxfn

Special Thanks to:
Henry (MinutePhysics): http://www.youtube.com/minutephysics
Destin (Smarter Every Day): http://www.youtube.com/smartereveryday
Greg and Mitch (ASAP Science): http://youtube.com/asapscience
Elise Andrew (I F***ing Love Science): http://youtube.com/iflscience

Thanks to everyone at RIT and Dickinson College who helped with the making of this video:
Rochester Institute of Technology
Robert Teese, Katelyn Wilkerson, Andrew Gillie, Andrew Stidwill

Dickinson College
This experiment was the brainchild of David Jackson based on a demo at Princeton.
Priscilla Laws, Catrina Hamilton-Drager, Maxine Willis

High-speed camera support:
Charles Zwemer and Bria Antoine

Music Licensed from CueSongs.com: The Temper Trap "Love Lost"
Lights Motion "Epilogue"