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  • [♪ INTRO]

  • Like any teacher will tell you, units are important.

  • Like, saying something is “100 degreesdoesn't mean anything.

  • Are you talking degrees Fahrenheit, or degrees Celsius, or just degrees of rotation?

  • Pretty big difference between those things!

  • Units are a major way we describe the world around us, but in conversation,

  • they can go by so quickly that we don't give them a second thought.

  • And maybe we should.

  • After all, many units are named after influential scientists.

  • So by looking at their stories and the discoveries they made,

  • we can get a sense of how we've learned so much about our universe.

  • On a different note, we can also get an idea of the kinds of voices that researchers historically valued.

  • Which means that, demographically, this list might not be a shocker:

  • It's a bunch of rich, white European men.

  • Rich, white European men who made some important discoveries.

  • Every day, millions of people use a temperature scale named after Daniel Gabriel Fahrenheit,

  • who was born in 1686 in what is now Poland; so probably I pronounced his name wrong.

  • He invented his scale back in 1724,

  • and it dominated scientific measurements right up until the middle of the 1900s.

  • So even though using it is something Americans get picked on for,

  • it's really no surprise that it remains widespread.

  • But really, “Fahrenheitwasn't Fahrenheit's biggest contribution to science.

  • Instead, he stood out because of his thermometers.

  • Thermometers in the 18th century were glass tubes filled with a liquid that expanded as it warmed up.

  • Typically, they contained water, oil, or purified alcohol, but those liquids weren't great at that job,

  • because they tended to freeze or boil at pretty mundane temperatures.

  • And once that happened, the thermometer was useless.

  • Fahrenheit improved this system in two big ways.

  • For one, he made his thermometers using mercury.

  • Mercury stays liquid across a much wider range of temperatures,

  • so you could use mercury thermometers in more situations.

  • The purity of mercury also varied less from place to place, meaning Fahrenheit's thermometers

  • would behave consistently regardless of where they were made and sold.

  • Admittedly, a few people had tried mercury thermometers before,

  • but mercury doesn't change size quite as much as other liquids,

  • which meant that it was harder to tell when the height changed in the tube.

  • So Fahrenheit's second improvement was to make his instruments with really thin glass tubes.

  • Whenever the mercury inside expanded even the tiniest bit, he could tell, and he could measure it.

  • Fahrenheit was able to make those narrow tubes over and over and over again,

  • and he could get mercury no matter where he sold them.

  • So his tools quickly spread all over Europe, as did the scale he invented to go with them.

  • Eventually, more precise and accurate thermometers were invented,

  • but the idea to use mercury stuck around, along with what was by then

  • commonly calledFahrenheit's scale”, or, as we know it today, Fahrenheit.

  • The watt is a unit of power, defined as the consumption of one joule of energy in one second.

  • For reference, one watt is about how much energy two bulbs consume

  • on an older string of Christmas lights, which is not very much at all.

  • So it's a little bit of energy, but James Watt, its namesake, was no chump.

  • He was a Scottish engineer and inventor in the late 1700s and early 1800s.

  • And his biggest claim to fame was his steam engine.

  • Kind of like what happened with Fahrenheit and mercury,

  • Watt did not invent the modern steam engine. That happened in the 1690s.

  • But he did make some significant improvements to them.

  • In 1764, he realized that the steam engines of the time wasted a lot of energy.

  • Steam engines work by boiling liquid water into steam,

  • which expands and pushes on something like a piston.

  • Pushing a piston once isn't generally that helpful, so the steam then gets collected, cooled down,

  • and condensed back into a liquid so that it can re-boil, push again, and repeat the cycle.

  • Original steam engines used the same chamber for both the heating and the cooling stages.

  • But Watt realized that constantly changing the chamber's temperature

  • wasted energy that could have gone into moving the piston.

  • After all, every time you cooled the chamber down,

  • you undid the work you had put in to heat it up in the first place.

  • To fix this problem, Watt designed an engine with separate boiling

  • and condensing chambers that was far more efficient than other engines of the day.

  • His engine would let you accomplish way more with the same amount of energy.

  • Like, if you could only burn a certain amount of coal each day,

  • you would get more out of it with Watt's design.

  • The engineer also made lots of tweaks and improvements to his work,

  • and had plenty of other inventions, too, including a photocopier.

  • But a better steam engine was his biggest legacy.

  • And because he did so much to improve how people use energy,

  • the unit of energy consumption was named after him in 1882.

  • At first, the ampere might sound less familiar than other units we've talked about so far.

  • But its nickname might ring more of a bell: the amp. Amps measure electric current;

  • the amount of electric charge moving past a point in a given length of time.

  • Cell phones draw one or two amps while they charge,

  • and each ampere is equal to about six million trillion electrons going by per second.

  • Which is a lot of charge.

  • The ampere is named after André-Marie Ampère,

  • who was a physicist that worked in France around 1800.

  • Scientists in Ampère's day were just starting to seriously study electricity,

  • and they'd already discovered that a current in a wire could affect a compass.

  • This sounds weird, but it proved that there was

  • some sort of connection between electricity and magnetism.

  • And Ampère wanted to understand that connection better.

  • He sent currents through two parallel wires and found that the wires either attracted

  • or repelled each other, depending on the direction of flow in each wire.

  • The wires acted like magnets with north and south poles,

  • except that Ampère didn't have any magnets in his experiments.

  • He only had these two wires carrying currents.

  • Eventually, he realized that current was like a magnet that you could turn on and off.

  • And today, this idea is used in electromagnets that spin motors

  • in everything from ceiling fans to car engines.

  • But this isn't where Ampère's work stopped.

  • After this, he also discovered a precise relationship between the amount of current

  • and the strength of the magnetism it produced; a relationship that is today known asAmpère's Law”.

  • His research into electromagnetism laid the groundwork

  • for some of the most important physics in the last two centuries;

  • work that has affected everything from power generation to computers.

  • So even though Ampère did a lot of research during his lifetime,

  • he's most famous for his electromagnetism work.

  • And since 1881, his name has been connected with the unit of electric current.

  • Hertz is a measure a frequency; how often something happens.

  • One hertz is a full cycle each second,

  • and although you can use this unit to describe a lot, it's often used in regards to sound.

  • Humans, for example, can generally hear sounds between about 20 and 20,000 hertz,

  • or between 20 and 20,000 full vibrations of the air every second.

  • This unit is named after German physicist Heinrich Rudolf Hertz,

  • who in the late 1880s became the first person to transmit and detect radio waves.

  • This happened when he was trying to confirm an idea from about 20 years earlier:

  • that a moving electric charge sends out waves of electricity

  • and magnetism that can move other charges around.

  • To do this, Hertz designed a series of experiments in which he looked for sparks;

  • the most obvious signs of moving electric charges.

  • First, he connected two circuits together and noticed that

  • when one sparked, the other often would, too.

  • Then, he physically separated the circuits, connecting only one to a source of electricity.

  • And he found that sparks in that one could still make sparks in the other.

  • Electricity wasn't flowing between them, but energy was.

  • This was the proof he was looking for that moving charges in the first circuit

  • were emitting waves that pushed charges around in the second.

  • To confirm this, Hertz even bounced the waves from one spark off a mirror

  • before they reached the second circuit.

  • And that still caused sparks.

  • By carefully going step-by-step, Hertz ruled out other possible causes of the sparks

  • and confirmed that the waves had the properties everyone predicted; properties like their frequency.

  • Specifically, these waves wiggled about 100 million times each second, which, for the record,

  • is the same frequency as the waves that carry the 100.0 station on modern FM radios.

  • Of course, Hertz did not invent the radio.

  • Going from sparks to songs took a bit more work.

  • But he was the first to measure these waves and to prove

  • that they were the same thing as regular light, just with a different frequency.

  • And even though he made lots of other important discoveries,

  • this alone was enough for the unit of frequency to be named in his honor in 1930.

  • Finally, we couldn't do a list show about units without talking about Celsius.

  • The Celsius temperature scale is named in honor of Anders Celsius.

  • And he's actually an odd one out on this list, because the scale with his name on it

  • isn't very closely related to what he spent most of his life doing.

  • He was first and foremost an astronomer, interested in auroras and the Earth's magnetic field.

  • But today, we remember Celsius because of a temperature scale he developed in 1742,

  • in which water froze at a hundred degrees and boiled at zero.

  • And you might think that I said that wrong, but we didn't, it's not the modern Celsius scale.

  • It's backwards! And arguably, a little more useful.

  • Other scientists besides Celsius had written scales like this before,

  • and they did it so that scientists got to write fewer negative numbers.

  • After all, no matter how oppressive summers can feel,

  • Earth's days never get hot enough to boil water, while in Sweden,

  • where Celsius worked, lots of days are near the point at which water freezes.

  • Putting the freezing point at 100 degrees and going up from there as it got colder

  • meant scientists recording common, everyday temperatures

  • wouldn't have half their numbers with minus signs and half without.

  • That meant fewer chances for a mistake when transferring data around.

  • Within a couple of years, though,

  • several people created versions of Celsius's scale with the modern numbering.

  • Because it turns out, they were fine with negatives after all.

  • Regardless, much like with Daniel Fahrenheit,

  • Celsius's scale became widespread because of how careful he was about calibrating it.

  • Air pressure, salinity, and lots of other factors can affect the temperature at which water changes states,

  • so Celsius was very specific about the conditions of the water as he was calibrating his scale.

  • That made his scale more reliable and easier to replicate than those

  • from other competing thermometers.

  • Some people started calling the degrees on this 0-100 scaleCelsiusafter its sort-of creator.

  • But others called itcentigrade”, which is Latin forhundred steps”.

  • The two names existed side-by-side until the scientific community officially named it after Celsius in 1948,

  • although you will still hear some people saycentigradeevery now and then.

  • Now, these five are hardly the only units named after people;

  • they're just some of the ones you'll hear most often.

  • But there are joules and newtons and pascals and curies and becquerels and farads and kelvin,

  • each with a scientist, a story, and a discovery or two hiding behind its inconspicuous name.

  • Of course, there are also a lot of weird units of measurement out there.

  • And if you want to know more about whether particle physicists can hit the broad side of a barn,

  • check out our video about barns and other obscure units that scientists are still using today.

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[♪ INTRO]

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