One of the most common physics misconceptions is that an unbalanced force causes constant motion. In truth, an unbalanced force leads to changes in motion - accelerations.

On the surface of Earth all objects accelerate downwards at the same rate - at least, they're supposed to. But we all know dust, pieces of paper, and feathers fall slower. This is of course due to the influence of air resistance. In this experiment we use an evacuated cylinder to test whether a coin and feather really do accelerate at the same rate.

Want to help plant 20M trees by 2020? Go to https://teamtrees.org #teamtrees
Huge thanks to all the YouTubers who organized this. My apologies for the repost.
These videos are from 2012 so my interest in trees goes back a long ways. I think these videos discuss two of the most interesting and amazing facts about our leafy friends: they are made mostly of CO2 (which comes from us breathing out amongst other sources) and they can transport water up a tube higher than any we can currently manufacture. So trees are out to get you. But we do much worse to them so we owe it to them to plant some more. 20 mil is a good start.

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

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...

Inspired by this article by Prof. Emily Oster: http://bit.ly/Cellcancer
Check out Audible: http://bit.ly/AudibleVe
Featuring Physics Girl: http://bit.ly/PhysGirl

Special thanks to Chris Gale and Physics Girl for filming this video.

Music by:
Amarante Music "One Last Time": http://bit.ly/VeAmarante
Kevin McLeod, Incompetech.com "Harlequin"

Do we take the Earth for granted? It gives us life and sustains us in the manner we're accustomed to, but we don't know the first thing about it: like where did it come from? And how did it form? Most people recognize that the Earth has a big explosion in its history, which they refer to descriptively as the 'Big Bang.' But there are two very good reasons why the Big Bang is not directly responsible for forming the Earth: 1) It happened 13.7 billion years ago. That's more than 9 billion years before the Earth formed (what happened during that time?), and 2) After the Big Bang the universe consisted of only Hydrogen and Helium - not great raw material for building the Earth. The truth is the big bang formed stars, which exploded and then (perhaps) formed more stars, which exploded and then formed our solar system, including the Earth. The early stars performed the vital role of making the heavier elements of which Earth is composed and we are made.

There is a common perception that weight and mass are basically the same thing. This video aims to tease out the difference between mass and weight by asking people what makes a car difficult to push. The standard answer is that it is difficult to push because it's heavy. But heaviness is a measure of weight, the gravitational pull of the Earth attracting the car to Earth's center. When the car is pushed on a flat road, the force of gravity does not oppose the motion. Instead the resistance felt is an indication of the car's mass which determines its inertia. Inertia is the property of matter that means it tends to resist acceleration - the greater the mass, the less the acceleration for a given amount of force.

Answer video: https://www.youtube.com/watch?v=BickMFHAZR0
The longest vertical straw you can use is 10.3 m http://www.youtube.com/watch?v=HUmZrtiXDik
This is because the weight of water in the straw must be supported by the pressure difference at its two ends. At the bottom, the pressure is atmospheric, and at the top, the lowest pressure you can create is a perfect vacuum (pressure = 0). Atmospheric pressure can support a water column about 10m high - BUT with 0 pressure at the top, the water would start boiling. This is called cavitation and it obviously can't be happening in trees.
After I posted the straw video, I received a lot of questions about how trees could be taler than 10m. I assumed there was a simple answer because there are plenty of trees taller than that. But as I asked around and read articles about it, I couldn't really find an explanation I was happy with.

Maybe there is not a continuous water column inside the tree, so each section only lifts water a little ways? This could be but it seems to require a series of pump mechanisms, and how would you join this pump sections together? Perhaps capillary action is holding the water up? But the xylem tubes in a tree seem too wide (~50 um) for this effect to be significant. Maybe osmotic pressure could push the water from below rather than sucking it up from above? But some trees live in mangroves, where there is much higher solute concentration in the sea water than in their roots, so osmosis would work the other way.

Eventually I spoke to a plant biologist and sorted this all out, but I wanted to give you a little back to school challenge. How do you think this could work?

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

Mars InSight will be the first to detect seismic activity on Mars’ surface, first to measure rate of heat transmitted from interior, first to dig nearly 5m down, first to measure magnetic fields on Mars’ surface, and first to use a robotic arm to place instruments on the surface of Mars (assuming it lands of course…)

If you want to watch the InSight landing “live” (with 4-minute speed of light time delay), go to: https://ve42.co/insight

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

Animations courtesy of NASA

Script and Filming with Raquel Nuno

Editing and graphics by Ignat Berbeci

Baby photos of our universe show huge early growth spurt!
Check out Audible: http://bit.ly/AudibleVe
Regression to the Mean: http://bit.ly/1lgZQAQ

Some clarifications:
- The lengthening of wavelengths is not strictly due to stretching by the expanding universe but by the way the photons were emitted and absorbed in different frames of reference.
- The effects of gravitational waves have been observed in the decaying orbital periods of some binary star systems, however detectors built to measure gravitational waves stretching and squeezing matter on Earth have not as yet detected them.
- In the video I sometimes use the term Big Bang to refer to the beginning of time as we know it. The Big Bang actually refers to the whole process from the formation of our universe, through inflation, to the expanding mass of plasma in the early universe (not just the first instant).
- Quantum gravity is by no means established by this observation but it is suggestive that General Relativity and Quantum Mechanics are working together here.

Thank you to Professor Geraint Lewis and Henry Reich for comments on earlier drafts of this video (even if I haven't accepted all of your corrections).

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

If you drop a heavy object and a light object simultaneously, which one will reach the ground first? A lot of people will say the heavy object, but what about those who know both will land at the same time? What do they think? Some believe both objects have the same gravitational pull on them and/or both fall to the ground with the same constant speed. Neither of these things is true, however. The force is greater on the heavy object and both objects accelerate at the same rate as they approach the earth, i.e. they both speed up but at the same rate.

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.

I always wanted to know why film looked better than video. Moving electronic images have as long a history but were invented for a different purpose. This video was sponsored by B&H Photo: https://www.bhphotovideo.com

Huge thanks to:

Richard Diehl, Video Labguy https://www.youtube.com/user/videolabguy
https://www.labguysworld.com

Branch Education for awesome animations
https://ve42.co/BranchEd

Minutephysics for mechanical TV animations
https://www.youtube.com/minutephysics

Mark Schubin
Engineer and explainer, SMPTE Life Fellow
https://www.smpte.org

This is a video I've long wanted to make, about what makes video look like video and, up until 10 years ago or so, not as appealing as film. I grew up with the two technologies (film and video) in parallel and to me they always seemed like two ways of achieving the same ends: recording and replaying moving images. But their histories are quite distinct. Film was always a way to capture moving images for later replaying. Video started out as a way to transfer images from one place to another instantaneously. This dates back to the first fax machine, mechanical TV, live broadcast tv and ultimately videotapes. This history focuses on the early decades of video and not the more recent switches to chip cameras and solid state storage. Maybe that's a story for another day.

Additional resources and references:

The Dawn of Tape: Transmission Device as Preservation Medium
https://ve42.co/dawnoftape

What Sparked Video Research in 1877? The Overlooked Role of the Siemens Artificial Eye
https://ve42.co/sparkvideo

Video Preservation Website:
http://videopreservation.conservation-us.org

Image Orthicon Tube:
http://interiorcommunicationse....lectrician.tpub.com/

Film vs Digital
https://stephenfollows.com/film-vs-digital/

Eyes of a Generation:
http://eyesofageneration.com

Television in the US:
http://www3.northern.edu/wild/th100/tv.htm

http://www.classictvinfo.com

Music from https://www.epidemicsound.com "Seaweed" "Capture a Picture 1" "Colorful Animation 4"

UV cameras expose a hidden world and reveal the incompleteness of our perception
The Physics Girl looks at sunscreen: https://youtu.be/GRD-xvlhGMc
How to make sunscreen from scratch: https://youtu.be/lMXAY5F28L0

In summary, ultraviolet light interacts differently with matter for a number of reasons:
1. Some pigments selectively absorb UV so they may appear white in the visible but dark in the UV. The pigments usually dissipate the UV energy as heat, though the breaking of bonds can also occur.
2. Fluorescent molecules absorb UV light and re-radiate that energy as visible light. This makes them look dark in the UV but glowing under black light.
3. Ultraviolet light scatters more than visible light because the wavelength is shorter and Raleigh scattering is proportional to the reciprocal of wavelength to the power of four.

Special thanks to HHMI BioInteractive for their awesome animations of melanocytes and how the melanin in melanosomes protect your DNA. To see the full video explaining how we get our skin color, check out: https://www.youtube.com/watch?v=VC0TL_lYLm8

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

References:

Overview of main UV effects:
Visualizing Rayleigh Scattering through UV Photography
https://journals.ametsoc.org/d....oi/pdf/10.1175/BAMS-

Arctic animals are photographed in the UV to increase visibility and get an accurate count:
Lavigne, D. (1976). Counting Harp Seals with ultra-violet photography. Polar Record, 18(114), 269-277. doi:10.1017/S0032247400000310

Absorption spectrum of melanin: http://www.cl.cam.ac.uk/~jgd1000/melanin.html

"The spectroscopy of human melanin pigmentation," by N. Kollias. In: Melanin: Its Role in Human Photoprotection, pp. 31 - 38. Valdenmar Publishing Co. (1995).

"Optical properties of human sclera, and their consequences for transscleral laser applications," by A. Vogel, C. Dlugos, and R. Nuffer, Lasers in Surgery and Medicine 11(4), pp. 331 - 340 (1991).

"The incidence and time-course of latanoprost-induced iridial pigmentation as a function of eye color," by P. Wistrand, J. Stjernschantz, and K. Olsson, Survey of Ophthalmology 41(S2), pp. S129 - S138 (1997).

Music by Epidemic Sound: https://www.epidemicsound.com "Spring Moods 5"

*Watch with headphones on!
Is 45 minutes really the longest anyone can stay in a perfectly silent, pitch-black room?
Support Veritasium on Patreon http://bit.ly/VePatreon
Check out Audible: http://bit.ly/AudibleVe
Want to watch the whole hour of silence? http://youtu.be/jr1UMFC9DV0

Many stories have circulated claiming the longest anyone has stayed in an ultra-quiet anechoic chamber is 45 minutes, the reason being any longer would drive you insane. To me this sounded like unsubstantiated rubbish, like the claim the Great Wall is the only manmade structure visible from space. So I put my own psyche on the line, subjecting myself to over an hour of the most intense quiet on Earth. No, this was not THE quietest room on Earth (-9dB) but it is one of the quietest, and the truth is once you put a person inside, they are by far the loudest thing in there so the sound rating of the room is irrelevant.

I was not surprised to find that I could stay in there for as long as I liked and feel perfectly fine. What was surprising is that my heartbeat was audible. You can hear it on the sound recording. Now I wasn't consciously aware of the sound of my heart while in the room, but I was more aware of the feeling of it beating.

Huge thank you to everyone at BYU: Duane Merrell, Spencer Perry, Cameron Vongsawad, Jazz Myers, Ann Clawson, and Robert Willes.

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'

Scientists like Prof Sinclair have evidence of speeding up, slowing, and even reversing aging.
Thanks to LastPass for sponsoring this video. Click here to start using LastPass: https://ve42.co/VeLP

What causes aging? According to Professor David Sinclair, it is a loss of information in our epigenome, the system of proteins like histones and chemical markers like methylation that turn on and off genes. Epigenetics allow different cell types to perform their specific functions - they are what differentiate a brain cell from a skin cell. Our DNA is constantly getting broken, by cosmic rays, UV radiation, free radicals, x-rays and regular cell division etc. When our cells repair that damage, the epigenome is not perfectly reset. And hence over time, noise accumulates in our epigenome. Our cells no longer perform their functions well.

To counter this decline, we can activate the body's own defenses against aging by stressing the body. Eat less, eat less protein, engage in intense exercise, experience uncomfortable cold. When the body senses existential threats it triggers longevity genes, which attempt to maintain the body to ensure its survival until good times return. This may be the evolutionary legacy of early bacteria, which established these two modes of living (repair and protect vs grow and reproduce). Scientists are uncovering ways to mimic stresses on the body without the discomfort of fasting. Molecules like NMN also trigger sirtuins to monitor and repair the epigenome. This may slow aging.

Reversing aging requires an epigenetic reset, which may be possible using Yamanaka factors. These four factors can revert an adult cell into a pluripotent stem cell. Prof. Sinclair used three of the four factors to reverse aging in the retinal cells of old mice. He found they could see again after the treatment.

Special thanks to:
Professor David Sinclair, check out his book "Lifespan: Why We Age & Why We Don't Have To"
Assistant Professor David Gold
Noemie Sierra (for polyp images)
Genepool Productions for telomere animations from Immortal: https://ve42.co/immortal
Epigenetics animations (DNA, histones, methylation etc) courtesy of: http://wehi.tv
Animation: Etsuko Uno
Art and Technical Direction: Drew Berry
Sound Design: Francois Tetaz & Emma Bortignon
Scientific Consultation: Marnie Blewitt
Courtesy of Walter and Eliza Hall Institute of Medical Research

Filming, editing and animation by Jonny Hyman and Derek Muller

Music from https://epidemicsound.com "Clearer Views" "Innovations" "A Sound Foundation" "Seaweed"
Additional music by Kevin MacLeod from https://incompetech.com "Marty Gots a Plan"