Los Estados Unidos firmaron el Tratado del Metro y basaron todas sus unidades tradicionales en las normas del Sistema Internacional. Además, la constitución de Utah de 1895 requería que el sistema métrico se enseñara en las escuelas. Este requisito fue derogado en 1987.

En 1875, EE. UU. firmó la Convención del Metro, que básicamente comprometió al país a utilizar el sistema métrico. A cambio, los científicos franceses enviaron dos cilindros de platino-iridio que pesan 1 kg a los EE. UU, en 1889 (conocidos por sus designaciones K4 y K20 de un conjunto de 40 objetos idénticos que se produjeron y enviaron a todo el mundo).
Por lo tanto, aunque todo lo que vea y compre en los EE. UU. generalmente se designa en libras, todos los pesos pueden rastrearse hasta el kilogramo K20 (aplicando un factor de conversión para obtener libras).

Cuando visité el Instituto Nacional de Estándares y Tecnología (NIST) y me acerqué al K20, que todavía se mantiene allí y se utilizaba para calibrar todos los estándares de masa en este país, hasta el año 2018. Esta fue una experiencia genial.

Muchísimas gracias a NIST, Ben Stein y Patrick Abbott.
https://www.nist.gov/
https://www.nist.gov/pml/weights-and-measures/si-units-mass

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Servicios de doblaje: Unilingo
Traductora: Paula Salomone
Voz de doblaje: Pato Lago, Diego Rivas
Ingeniero de sonido: Gastón Adriel Álvarez
Edición y post-producción de video: Juan Caille Tornquist
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#veritasiumenespañol

Acompáñennos en este fascinante viaje a través del mundo de la ciencia. Les presentaremos experimentos asombrosos para que se diviertan mientras adquieren nuevos conocimientos ¡Que lo disfruten!

NOTE: This video will appear in a playlist on Smarter Every Day hence the references to Veritasium. Destin does lots of cool science stuff - check out his channel if you haven't already http://www.youtube.com/destinws2

We have been collaborating on rotational motion, which is timely for some of the videos I've been doing lately. In this video I talk about gyroscopic precession - the "wobbling" of a spinning top around its axis.

This is caused by the torque due to the object's weight. The big idea is that the torque vector increases angular momentum in the direction of torque. So if there is no angular momentum initially, it will cause the system to swing in such a direction that it is rotating with new angular momentum in the direction of the torque. However, if there was angular momentum to begin with, the torque will change the direction of that angular momentum by causing precession.

We have just seen the first image of a black hole, the supermassive black hole in the galaxy M87 with a mass 6.5 billion times that of our sun. But what is that image really showing us?

This is an awesome paper on the topic by J.P. Luminet:
Image of a spherical black hole with thin accretion disk
Astronomy and Astrophysics, vol. 75, no. 1-2, May 1979, p. 228-235
https://ve42.co/luminet

Using my every day intuition I wondered: will we see the "shadow" of the black hole even if we're looking edge on at the accretion disk? The answer is yes because the black hole warps space-time, so even if we wouldn't normally be able to see the back of the accretion disk, we can in this case because its light is bent up and over the black hole. Similarly we can see light from the bottom of the back of the accretion disk because it's bent under the bottom of the black hole. Plus there are additional images from light that does a half turn around the black hole leading to the inner rings.

What about the black hole "shadow" itself? Well initially I thought it can't be an image of the event horizon because it's so much bigger (2.6 times bigger). But if you trace back the rays, you find that for every point in the shadow, there is a corresponding ray that traces back to the event horizon. So in fact from our one observing location, we see all sides of the event horizon simultaneously! In fact infinitely many of these images, accounting for the virtually infinite number of times a photon can orbit the black hole before falling in. The edge of the shadow is due to the photon sphere - the radius at which light goes around in closed orbits. If a light ray coming in at an oblique angle just skims the photon sphere and then travels on to our telescopes, that is the closest 'impact parameter' possible, and it occurs at sqrt(27)/2*r_s

Huge thanks to:
Prof. Geraint Lewis
University of Sydney https://ve42.co/gfl
Like him, I'm hoping (predicting?) we'll see some moving images of black holes tomorrow

Prof. Rana Adhikari
Caltech https://ve42.co/Rana

Riccardo Antonelli - for excellent images of black holes, simulations and ray-tracing code, check out:
https://ve42.co/rantonels

The Event Horizon Telescope Collaboration
Check out their resources and get your local link for the livestream here: https://ve42.co/EHT

Special thanks to Patreon supporters:
Donal Botkin, Michael Krugman, Ron Neal, Stan Presolski, Terrance Shepherd, Penward Rhyme

Filming by Raquel Nuno
Animation by Maria Raykova

Is the future of the universe already determined?
Vsauce tackles "What is Random?": https://youtu.be/9rIy0xY99a0

Special Thanks to: Prof Stephen Bartlett, Prof Phil Moriarty, Prof Andrea Morello, Prof Tim Bedding, Prof Michio Kaku, A/Prof Alex Argyros, Henry Reich, Vanessa Hill, Dianna Cowern, George Ruiz and Mystery Cat. Views expressed in this video are not necessarily those of the amazing experts listed above but their advice was invaluable in making this video.

Quantum simulation by PhET:
https://phet.colorado.edu/en/s....imulation/quantum-tu

Music by
Jake Chudnow: https://soundcloud.com/jakechudnow
Amarante Music: https://soundcloud.com/amarantemusic

DNA animations by http://www.wehi.tv

Space animations by NASA

Topic inspired by The Information - a history, a theory, a flood by James Gleick

Filmed on location at the University of Sydney, Washington DC and LA

The physics behind Kelvin's Thunderstorm explained. No, it is not a practical way of generating electricity, which is why we use turbines at hydro stations.

This video goes into more detail about the phenomenon demonstrated in this Hunger Games collab video: http://youtu.be/Rwa26CXG1fc

Huge thanks to the Royal Institution, Professor Frank James, and Katie Atmore for filming.
For the Sixty Symbols version of this experiment click http://bit.ly/RGfLY5

Michael Faraday created the first electric generator in 1831 using a coil of wire and a permanent magnet. When the magnet was moved relative to the coil, current was induced in the coil. A similar experiment can be performed with a copper tube and a magnet. Although copper is not magnetic, it is a conductor. As the magnet falls through the pipe, the magnetic field changes over different sections of the pipe. This induces swirling currents (called eddy currents), which create a magetic field that opposes the motion of the magnet. This means work must be done to move the magnet through the pipe. This work generates the electrical energy, which is then dissipated as thermal energy in the pipe. The same basic principle is used to generate electricity throughout the world: moving a magnet inside copper coils.

Experiments A Cappella http://bit.ly/TtdflV
Where Did The Earth Come From http://bit.ly/VQBzQJ
The Coastline Paradox http://bit.ly/TIapxM
Microwave Grape Plasma http://bit.ly/QkCwUt


Music by Kevin McLeod (http://www.incompetech.com) Sneaky Snitch and Danse Macabre

The answer to the question - what happens to a tennis ball tied to the bottom of a slinky after the top of the slinky is let go?

For a great explanation, check out Rhett Allain's analysis here: http://www.wired.com/wiredscie....nce/2011/09/modeling

The merging of two neutron stars was detected by gravitational waves and then by telescopes in all parts of the electromagnetic spectrum. This is a historic detection as it demonstrates:
- the first gravitational waves detected from inspiraling neutron stars
- the first joint observation by gravitational wave and electromagnetic wave astronomy
- identification of a gamma ray burst in conjunction with merging neutron stars
- how gravitational waves and gamma rays can be used together to locate their source

All evidence so far indicates that the data support General Relativity.

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

Graphics from:
Jets and Debris from a Neutron Star Collision
This animation captures phenomena observed over the course of nine days following the neutron star merger known as GW170817. They include gravitational waves (pale arcs); a near-light-speed jet that produced gamma rays (magenta); expanding debris from a "kilonova" that produced ultraviolet (violet), optical and infrared (blue-white to red) emission; and, once the jet directed toward us expanded into our view from Earth, X-rays (blue).
Credit: NASA's Goddard Space Flight Center/CI Lab

Virgo Helps Localize Gravitational-Wave Signals
Sky localizations of gravitational-wave signals detected by LIGO beginning in 2015 (GW150914, LVT151012, GW151226, GW170104), and, more recently, by the LIGO-Virgo network (GW170814, GW170817). After Virgo came online in August 2017, scientists were better able to localize the gravitational-wave signals. The background is an optical image of the Milky Way. The localizations of GW150914, LVT151012, and GW170104 wrap around the celestial sphere, so the sky map is shown with a translucent dome.
Credit: LIGO/Virgo/NASA/Leo Singer (Milky Way image: Axel Mellinger)

Variety of Gravitational Waves and a Chirp
The signal measured by LIGO and Virgo from the neutron star merger GW170817 is compared here to previously detected binary black hole mergers. All signals are shown starting at 30 Hertz, and the progression of GW170817 is shown in real time, accompanied by its conversion to audio heard at the end of the movie. GW170817 was observable for more than 30 times longer than any previous gravitational-wave signal.
Credit: LIGO/University of Oregon/Ben Farr

LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions to the project.

More than 1,200 scientists and some 100 institutions from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration and the Australian collaboration OzGrav. Additional partners are listed at http://ligo.org/partners.php

The Virgo collaboration consists of more than 280 physicists and engineers belonging to 20 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with the University of Valencia; and the European Gravitational Observatory, EGO, the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef.

SYNCHRONIZE WITH DESTIN’S VIDEO: http://bit.ly/NorthernSwirl
Both videos on one page (for desktop): http://bit.ly/ToiletSwirl
Subscribe to Smarter Every Day: http://bit.ly/SubscribeSED
Click to tweet: http://bit.ly/ToiletSwirlTWT

Some notes:
We each repeated the experiment 3 times, and got the same results every time. For those of you who might be skeptical, great! A right circular prismatic kiddie pool is only $10 and you can do the experiment for yourself at your latitude. There's really no reason you shouldn't do it for yourself.

Veritasium on Instagram: http://instagram.com/veritasium
Patreon Support Link: http://www.patreon.com/veritasium
Twitter: http://twitter.com/veritasium
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Smarter Every Day Instagram: http://instagram.com/smartereveryday
Patreon Support Link: http://www.patreon.com/smartereveryday
Twitter: http://twitter.com/smartereveryday
www.facebook.com/SmarterEveryDay

Gordon McGladdery did all of the sound design for the video. We used two songs from other artists (licensed of course). Derek split the first one up so it fades from video to video, and Gordon split the instruments up on the second one. There are violins on one video and percussion on the other for example. It's really neat.

The neat earth animation at the beginning and the synchronizing timer was made by http://eisenfeuer.com/. He also made still images of the earth from the top and the bottom.

Thanks to Vanessa for filming in Sydney: http://youtube.com/braincraftvideo

MORE INFO:

There was a study performed at MIT years ago (http://web.mit.edu/hml/ncfmf/09VOR.pdf) that explained the physics involved. We repeated some of these demonstrations, but on opposite sides of the globe…and in a way that can be easily understood.
This site is a great resource on the Coriolis effect and ways people have gotten it wrong:
http://www.ems.psu.edu/~fraser/Bad/Ba...

Watch this first! https://www.youtube.com/watch?v=QD3hbVG1yxM
Follow on Twitter: https://twitter.com/veritasium
Follow on Facebook: https://www.facebook.com/veritasium

Special thanks to the Department of Earth, Planetary and Space Sciences, especially Gary for helping source the equipment and Raquel for filming.

The definitive answer about the direction water swirls in two hemispheres
Sync the videos yourself: http://toiletswirl.com

For the record Destin and I repeated the experiment 3-4 times each in each hemisphere and got the same results every time.

The idea that water going down a drain or flushed down a toilet swirls in opposite directions in the Northern and Southern Hemispheres has a long history. But few have ever done the experiment. Destin from Smarter Every Day and I performed identical experiments in the Northern and Southern hemispheres. What we found is the direction of water swirl in a toilet, sink, or bathtub is determined by other sources of angular momentum. However if the body of water is big enough, e.g. a kiddy pool, and left still for long enough (at least 24 hours), then the Coriolis effect is observable with water swirling counterclockwise in the Northern hemisphere and clockwise in the Southern hemisphere.

Veritasium on Instagram: http://instagram.com/veritasium
Patreon Support Link: http://www.patreon.com/veritasium
Twitter: http://twitter.com/veritasium
http://www.facebook.com/veritasium

Smarter Every Day Instagram: http://instagram.com/smartereveryday
Patreon Support Link: http://www.patreon.com/smartereveryday
Twitter: http://twitter.com/smartereveryday
www.facebook.com/SmarterEveryDay

Gordon McGladdery did all of the sound design for the video. We used two songs from other artists (licensed of course). Derek split the first one up so it fades from video to video, and Gordon split the instruments up on the second one. There are violins on one video and percussion on the other for example. It's really neat.

The neat earth animation at the beginning and the synchronizing timer was made by http://eisenfeuer.com/. He also made still images of the earth from the top and the bottom.

Thanks to Vanessa for filming in Sydney: http://youtube.com/braincraftvideo

MORE INFO:

There was a study performed at MIT years ago (http://web.mit.edu/hml/ncfmf/09VOR.pdf) that explained the physics involved. We repeated some of these demonstrations, but on opposite sides of the globe…and in a way that can be easily understood.
This site is a great resource on the Coriolis effect and ways people have gotten it wrong:
http://www.ems.psu.edu/~fraser/Bad/Ba...

These are the molecular machines inside your body that make cell division possible. Animation by Drew Berry at the Walter and Eliza Hall Institute of Medical Research. http://wehi.tv

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

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

Every day in an adult human roughly 50-70 billion of your cells die. They may be damaged, stressed, or just plain old - this is normal, in fact it’s called programmed cell death.

To make up for that loss, right now, inside your body, billions of cells are dividing, creating new cells.

And cell division, also called mitosis, requires an army of tiny molecular machines.DNA is a good place to start - the double helix molecule that we always talk about.

This is a scientifically accurate depiction of DNA. If you unwind the two strands you can see that each has a sugar phosphate backbone connected to the sequence of nucleic acid base pairs, known by the letters A,T,G, and C.

Now the strands run in opposite directions, which is important when you go to copy DNA. Copying DNA is one of the first steps in cell division. Here the two strands of DNA are being unwound and separated by the tiny blue molecular machine called helicase.
It literally spins as fast as a jet engine! The strand of DNA on the right has its complimentary strand assembled continuously but the other strand is more complicated because it runs in the opposite direction.
So it must be looped out with its compliment strand assembled in reverse, section by section. At the end of this process you have two identical DNA molecules, each one a few centimeters long but just a couple nanometers wide.

To prevent the DNA from becoming a tangled mess, it is wrapped around proteins called a histones, forming a nucleosome.
These nucleosomes are bundled together into a fiber known as chromatin, which is further looped and coiled to form a chromosome, one of the largest molecular structures in your body.
You can actually see chromosomes under a microscope in dividing cells - only then do they take on their characteristic shape.

The process of dividing the cell takes around an hour in mammals. This footage is from a time lapse. You can see how the chromosomes line up on the equator of the cell. When everything is right they are pulled apart into the two new daughter cells, each one containing an identical copy of DNA.
As simple as it looks, this process is incredibly complicated and requires even more fascinating molecular machines to accomplish it. Let’s look at a single chromosome. One chromosome consists of two sausage-shaped chromatids - containing the identical copies of DNA made earlier. Each chromatid is attached to microtubule fibers, which guide and help align them in the correct position. The microtubules are connected to the chromatid at the kinetochore, here colored red.
The kinetochore consists of hundreds of proteins working together to achieve multiple objectives - it’s one of the most sophisticated molecular mechanisms inside your body. The kinetochore is central to the successful separation of the chromatids. It creates a dynamic connection between the chromosome and the microtubules. For a reason no one’s yet been able to figure out, the microtubules are constantly being built at one end and deconstructed at the other.
While the chromosome is still getting ready, the kinetochore sends out a chemical stop signal to the rest of the cell, shown here by the red molecules, basically saying this chromosome is not yet ready to divide
The kinetochore also mechanically senses tension. When the tension is just right and the position and attachment are correct all the proteins get ready, shown here by turning green.
At this point the stop signal broadcasting system is not switched off. Instead it is literally carried away from the kinetochore down the microtubules by a dynein motor. This is really what it looks like. It has long ‘legs’ so it can avoid obstacles and step over the kinesins, molecular motors walking the other direction.

Studio filming by Raquel Nuno

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

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"

Compliant mechanisms have lots of advantages over traditional devices. SimpliSafe is awesome security. It's really effective, easy to use, and the price is great. Check out SimpliSafe here: https://simplisafe.com/veritasium

I visited the Compliant Mechanisms Research group at Brigham Young University and spoke to Professor Larry Howell:
https://www.compliantmechanisms.byu.edu

At the above link, you can download 3D-print files to make some of the objects in the video, plus learn more about compliant mechanisms.

What I learned about compliant mechanisms I summarize in the 8 P's of compliant mechanisms:

1. Part count (reduced by having flexible parts instead of springs, hinges)
2. Productions processes (many, new, different enabled by compliant designs)
3. Price (reduced by fewer parts and different production processes)
4. Precise Motion (no backlash, less wear, friction)
5. Performance (no outgassing, doesn't require lubricant)
6. Proportions (reduced through different production processes)
7. Portability (lightweight due to simpler, reduced part count designs)
8. Predictability (devices are reliable over a long period of time)

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

Animation by Alan Chamberlain

The US signed the metre convention and bases all customary units on SI standards. As an aside, the Utah constitution from 1895 required the metric system to be taught in schools. This requirement was repealed in 1987. ¯\_(ツ)_/¯

Huge thanks to NIST, Ben Stein and Patrick Abbott.
https://www.nist.gov/
https://www.nist.gov/pml/weights-and-measures/si-units-mass

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

Back in 1875 The US signed the Metre Convention, which basically committed the country to use the metric system. In return, French scientists sent two platinum-iridium cylinders that weigh 1kg to the US in 1889 (known by their designations K4 and K20 from a set of 40 identical objects that were produced and sent around the world). So even though everything you see and buy in the US is usually reported in pounds, all weights are traceable back to the K20 kilogram (by applying a conversion factor to get to pounds).

When I was in DC a few weeks ago, I visited the National Institute of Standards and Technology (NIST) and got up close with K20, which is still kept there and used to calibrate all mass standards in this country. I thought it was pretty cool.

Edited by Bill Connor

The strange thing about high jump is that the technique changed dramatically after 1968, when Dick Fosbury used his trademark flop to win the gold medal at the Olympics in Mexico City.
Previously the scissors and straddle had been the most common jumping technique, but after the introduction of safer landing matts, the new unorthodox Fosbury Flop became the jump of choice. There are good physical reasons for this - the style allows the jumper to pass over the bar while his or her centre of mass actually passes below the bar.

Huge thanks to Elly (Appchat http://bit.ly/NxAMlX ) for filming, editing, and music!

numberphile http://bit.ly/numberphile
efit30 http://bit.ly/O4CMme
appchat http://bit.ly/NxAMlX
erikaanear http://bit.ly/MdyUzQ
whoisjimmy http://bit.ly/LtFzpW
minutephysics http://bit.ly/Muh6CC
1veritasium http://bit.ly/MrupzL

Remarkably little is known about great white sharks, but they are similar to humans in a lot of ways - they give birth to live young, maintain a higher body temperature than their surroundings and they are apex predators. There are also many misconceptions about these sharks: people think they don't get cancer and that they reside mainly in shallow waters near beaches. In this video I summarize some of the most interesting things I learned about sharks on my cage diving adventure.

Special thanks to Rodney Fox Shark Expeditions for making this trip possible: http://bit.ly/rodneyfox

Thanks also to Tourism South Australia for facilitating the trip: http://bit.ly/1aq9MgV

Chris Cassella or C² as he is known after this trip was a shark spotter extraordinaire. He also took some of the best shark footage in this video. It was his idea to go on this expedition, which was definitely a once in a lifetime experience, so I am in his debt. Chris, I look forward to going on more great adventures with you. Check out Chris's facebook page ScienceAlert http://on.fb.me/18nhyLp

NEW CHANNEL! http://youtube.com/sciencium

For a long time we thought the Moon was completely dry, but it turns out there are actually three sources of lunar water.
Thanks to Google Making and Science for supporting the new channel! http://youtube.com/makingscience

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

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

References:
Great history of water on the moon: https://arxiv.org/pdf/1205.5597.pdf

Filmed by Raquel Nuno

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