The (Arguably) Most Important Instrument in Physics

The (Arguably) Most Important Instrument in Physics

[♪ INTRO] Alright, honesty time;
here comes the true-true train. You probably don’t think much about thermometers. If you have one, it’s likely for when you’re
sick, or someone in your house is sick, or maybe it’s hanging in the backyard somewhere
as a decoration. But get ready to appreciate these things a
lot more. Because in the 1800s, accurate thermometers
helped give us one of the most important ideas in all of
science: the conservation of energy. These days, you’re told to “conserve energy”
all the time, but this idea is not about turning off the
lights or limiting your air conditioning. Instead, it says that energy can change forms
and it is never created or destroyed, and it shapes the way we approach almost everything
in physics. Lots of people, spread out over centuries,
helped discover energy conservation. But one of the most important was a physicist
named James Prescott Joule. And he could not have done his groundbreaking
work without a good thermometer. Essentially, Joule showed that energy can take
different forms, like heat, electricity, and motion. And while that might sound obvious today,
it was a very big deal 200 years ago. In the early 1800s, physicists thought “energy”
only meant “movement”, and that it was completely separate from other
scientific ideas. For example, many people thought that heat
was some kind of fluid. And that made the whole concept of energy
kind of useless. Since today’s scientists know that energy
can take different forms, they can use it to understand all kinds of
systems. Like, you wanna understand levers? You could use complicated ideas like forces
at angles making torques, or you could use the fact that balanced levers balance
potential energy; energy that’s stored in a system. Or, wanna know how long it’s gonna take
your car to stop? If you know that brakes turn kinetic energy
into thermal energy, that is, they turn movement into heat, you
will work it out much faster than by calculating all of the complex molecular interactions
between brakes and rotors. To modern scientists, converting between forms of energy is a natural way of cutting past a million tiny details, and it helps them get the big picture of what’s
actually happening in the world. Except, it took them a while to figure this
out. And that is where James Joule comes in. He was an English physicist and experimentalist,
and while he had done other research before, his adventure with energy conservation started
when he found some new ways of making heat. First, he realized that you can make heat
using this new-fangled “electricity” thing that everyone was talking about in the 1800s. That might be a surprise if you’re used
to your laptop keeping your legs warm in the winter, but
this was 1840. Michael Faraday had invented the electric
generator less than a decade earlier, when he realized that moving magnets and wires
near each other forced a current through the wire. So it’s not like we knew a lot about how
electricity worked at this point. In his experiment, Joule used one of those
generators to prove that one part of a circuit could heat up without
other parts cooling down. If heat was a fluid like many people thought
at the time, that shouldn’t have been possible. The heat should have just
moved from one place to another. Then, Joule had a thought: If moving magnets
and wires could turn into electricity that could turn into heat, maybe there wasn’t
anything special about the magnets and the wires. Maybe movement could be turned directly into
heat, without any electricity in the middle. So he used his and other people’s experiments
to calculate how much something would have to move in a tank of
water to change the water’s temperature. Then, he tested his prediction by making a
falling weight tug on a rope that was connected to a wheel in a tank of water. When the weight fell, it pulled the rope,
which spun the wheel. Nowadays, we’d say he converted potential
energy of the weight into kinetic energy of the wheel into the
thermal energy of the water. Back then, they would say that he was just
wasting time. But Joule was a rare combination of careful,
clever, and persistent. He had calculated that the water’s temperature might change by half a degree Fahrenheit or less;
about a quarter of a degree Celsius. And that was too tiny to reliably measure
by eye with the thermometers of the day. To get around this, Joule worked with some
of the best instrument-makers in Europe to build thermometers with incredibly fine
temperature differences marked on them. Then, they built a sort of traveling microscope
that moved along the thermometers that let Joule quickly read between those
lines. With this method, Joule claimed he could measure
temperature differences as small as 1/200th of a degree Fahrenheit,
which scientists then and now think was a little optimistic, but probably
not by too much. Today, it’s actually hard to confirm how
good they were, because the originals were lost in a fire,
and no one knows exactly how they were made. But regardless, Joule’s thermometers were
certainly better than anything else around. In fact, they were so sensitive that scientists
repeating Joule’s experiment with different instruments in the 1990s discovered they had to be careful that their body heat
didn’t throw off measurements. But ultimately, with his thermometers and
microscope, Joule proved himself right. Turning his wheel heated up the water exactly
as much as he expected, which meant that heat and motion could be
converted into each other. And combined with his earlier work, it meant that heat, motion, and electricity
all had something in common. People did not accept his work right away, but Joule kept demonstrating that his results
were consistent. As he worked, other scientists also started
connecting his research to other discoveries, like experiments that people had been doing
with steam engines, where crushing a gas heated it up. And eventually, Joule and others developed
the idea of energy conservation: that heat, motion, and electricity were just
some of the different forms of this thing called “energy” that could be changed between types without
changing its absolute amount. James Joule’s experiments helped found thermodynamics:
the science of how energy moves around. And for his efforts, in 1882, when Joule was
in his early 60’s, scientists proposed a new unit of energy:
the Joule. Today, the study of physics would be, like,
dramatically different without energy conservation. This idea helps us understand thousands of
systems, and it can even help us tackle the biggest challenges facing our planet,
like climate change. Really, by the late 1800s, scientists were
already using energy conservation to think about the Earth’s climate. They knew that some gases blocked infrared
radiation, that is, light energy, better than others. So they started wondering what would happen
when humans put more of those gases into the air. Thanks to Joule and others, they didn’t
have to add up the effects of each carbon dioxide and water molecule, because energy conservation
let them cut to the chase: If the atmosphere lets less energy into space, that means more must stay here on Earth, and
Earth has to get warmer as a result. So the next time you’re looking at a thermometer, take a second to appreciate that beautiful
piece of engineering! It has taught us so much! It might seem like a simple instrument, but
science would not be the same without it. If you want to learn more about stories like this, you can head over to one of our sister channels:
Crash Course. There, I hosted a whole series called History
of Science, where we explored how we came to understand, like, basically
all of the things we currently understand. You can find it by clicking the card at the
end of this video, or at And as always, thanks for watching this episode
of SciShow. [♪ OUTRO]

100 thoughts on “The (Arguably) Most Important Instrument in Physics

  1. That global warming bit made this video seem propaganda-ish. On the side of science and all rationality, but propaganda none the less.

  2. 1:08 In the early 1800s, physicists thought “energy” only meant “movement”
    5:51 Joule’s experiments helped found Thermodynamics, the science of how energy moves around

  3. Wouldn’t it have been common knowledge that motion could be converted to heat through friction since you can do that by just rubbing your hands together?

  4. Good video but this should have been titled 'How Joule Introduced Energy Conservation'. This video has very little to do with thermometers.

  5. I thought it was Watt that defined the Btu as 755 ft pounds utilizing the weigh churning water method?

  6. I have a pet chinchilla, two guinea pigs, two rabbits, and two sugar gliders. My thermometer gets a LOT of use. There is a VERY narrow range where they'll all be happy. I have to keep the temperature as close to 80 as possible without letting it actually hit 80.

  7. 3:14 That sounds like people have never figured out to rub their hands together when it's cold to warm them up before Joule came around and told them lol.

  8. Since heat is vibrating molecules/atoms, electricity is the flow of electrons, light/electromagnetic radiation is the flow of photons, gravitons carry the energy of gravity, and chemical energy is driven by positive and negative charges which cause movement among atoms, would the old idea of energy just being movement not hold true?

  9. or believe to know as Gödel wonce said as more i believe to know as more i figure out what i dont know happy weekend

  10. Already watched history of science, physics, biology, chemistry, psychology,philosophy, Anatomy and even world history (watching sociology now)

  11. Wait, people don't check outside temps every day? o.O (And that brake animation was *so wrong*. The calipers don't move.)

  12. Have they never rubbed their hands against each other on a cold day? Movement, friction, heat. Or is this different than the wheel in the water?


  14. Modern thermometers are nothing like the ones back in the day.
    These days we use alcohol or some other non toxic chemical that is not as accurate as the mercury based ones.

  15. Is there a part 2 coming? Expanding metal coil thermometers… digital thermometers… & more. Barometers would also be a relative subject to cover. Thank you I ❤ THERMOMETERS!

  16. Had to throw in the stupid climate change hoax at the end. Up to the point, it was an interesting presentation. And by the way, where would we be now if not for White men?

  17. Best video I’ve seen in a good while! Somehow my physics courses in college never covered any of this. I am so grateful for this knowledge! Much love!

  18. But why does it matter that 'energy' is conserved when free energy isn't conserved and always decreases?

    But what even is energy? It's often taught that energy is the ability to do work. But if free energy is the energy that is avilable to do work, and 'energy' is the free energy plus the energy unavailable to do work, then that seems contradictory.

  19. "Maybe movement could be turned directly into heat, without electricity in the middle." Ummmmm… Rubs two sticks together to make fire

  20. People must have known that movement could be turned into heat every time they rubbed their hands together to warm them through friction.

  21. It is really hard overestimate the importance of the concept of energy today.
    One of the derivation of the ideal gas law involves the concept of energy.
    Energy is also a major part of the interpretation of the schrodinger equation, one of the most important early equation in quantum mechanics.
    Energy is also a key part of lagrangian mechanics an alternative model to newtonian mechanics, and of course we can't froget the famous E=mc^2 (which is by the way just a special case of a more genral fomula).
    There are endless ways in which energy and energy conservetion help us in modern day physics.

  22. If atmospheric CO2 really trapped that much heat in paractice (and it is disputable if you look at the entire picture of what is in the atmosphere and how it behaves) then photovoltaic solar cells are a really bad idea because they are almost black and convert 70% of the visible light hitting them into heat that would then be trapped, whereas the visible light can radiate back out into space if reflected off other objects, plants and soils which are rarely that dark. You can't have it both ways.

  23. I have a few old mercury based thermometers in the hazardous section of my mineral collection. It sits alongside a 800ml vial of liquid form mercury and a piece containing 5 cinnabar crystals on a surface of quartz, all in a enclosed glass temp controlled display setting.

    Mercury is cool as frick, but yeah make sure you are aware of how to store it properly if you don't want to end up like the hatter.

  24. I would like to see a video on what humans would do if all equipment, technology, textiles etc… were taken from them, but had the knowledge and expertise of everything they needed to restart civilisation. How do humans even begin to extract metals from rock, or even detect it's even there to begin with… that would be a cool video on the history of science.

  25. I SAW that Delete This Reference and I cant believe you said that on SciShow!!! (frickin true-true train!!)

  26. ummm, why would they think that heat is a fluid and why do they need this electric current experiment to prove otherwise?
    when you burn wood, there is nothing cooling off just the same as with the experiment with the wires

  27. Movement into heat…. I mean I could prove it with a stick and a wooden board… That's how fire was created… By 'moving' the stick very quickly to catch ember… Damn these guys

  28. I don't know why they aren't pitching their new channel ,but there's a new channel hosted by HANK! It's called Journey to the Microcosmos.

  29. My step dad worked as a maintenance man at a college. He became obsessive about thermometer readings in the classrooms. Who gives a damn about what a thermometer says? I don't.

  30. You're like a religious school that "sanctify" maths books by placing bible quotes on every page with your linking the history of Joule to global warming.

  31. If I didn't know better I'd almost think that people in the 1800s never rubbed their hands together when they were cold

  32. It seems that many/most episodes of SciShow have become a mouthpiece for the global warming lobby. BTW it is so presumptuous to think that humans can influence the climate or the weather.

  33. A hilarious book, "How to invent everything: A guide for the stranded time traveler", dedicates a comparative many pages to developing thermometers, barometers, and clocks so that you can invent the entire rest of science.

  34. If people used to belive was a fluid, then how did they explain that your hands get warm when you rub them together? People do it all the time when it's cold so they must have thought about it.

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