National prototype kilogram K20 replica

National prototype kilogram K20, one of two prototypes stored at the US National Institute of Standards and Technology in Gaithersburg, Maryland, which serve as primary standards for defining all units of mass and weight in the United States. This is a replica for public display, shown as it is normally stored, under two bell jars.

In the late 1800’s, a small, well-formed cylinder composed of platinum and a little iridium (the same alloy used in fine platinum jewelry today) was defined by the international scientific community to have a mass of exactly one kilogram. This was not a special rock dug up from the Earth, nor a once-in-a-lifetime meteorite fallen from the heavens, but a man-made object that was bestowed this great and important property to be used by generations of scientists and non-scientists. (Happy 125th Birthday, Kilogram.)

For myself as a student of physics, and likely with many professional scientists in the 20th Century, there was a lingering empty feeling from this type of “pull-it-out-of-the-air” proclamation for something fundamental to so many calculations and theories describing how Nature works. The speed of light, c, is a fundamental number that is directly measurable (try it yourself with chocolate), the definition of a unit of time in seconds, s, is directly measured from a naturally occurring phenomenon with unprecedented regularity (originally based on the rotation of the Earth, with all of its wobbles; now on the energy level transition in an atom near absolute zero temperature), and the meter is marked off (since 1983) by a measurable distance traveled by light in a fraction of a second. So, most other important units are built up from more fundamental definitions. Yet, the kilogram, with its smooth lump of metal, is still thrown into this fundamental mix.

For example, the Newton, N, is a unit of force measured from the well-loved equation F = ma, and carries the units of kilogram · meters per unit second. If the value of one kilogram was set only as the collective whim of humanity well over one hundred years ago, then what does that say about every calculation of force since that time? Well, probably not much, since we’ve been working just fine with it ever since. If the fundamental value changes, it just scales all other values with it. However, it might just be nice, or more reasonable, or more scientific to have the value of the kilogram defined from other measurable fundamental values so it may never be questioned or changed (or stolen for a private collection, or fall through a crevice in the Earth after a quake never to be found again).

The mission of cleaning up the fundamental definition of the kilogram has been underway for many years with an international resolution declared in 1999, at the turn of the century. Now, this latest collective whim of scientists is to derive the value of the kilogram from a very fundamental number found in the realm of quantum mechanics, called Planck’s constant, h.

First described during the turn of the previous century, in 1900, by Max Planck, this constant represents the ratio of the energy (E) of an atomically-small oscillating object to its frequency (f) of vibration. The relationship, called the Planck-Einstein relation, E = hf, became a basic underpin to the development of quantum mechanics. The proportionality constant h made an appearance in a plethora of key equations that came to describe the Universe at its tiniest scales, including the counter-intuitive notion that very small things can behave like a wiggling wave and a bouncing particle simultaneously.

The actual value of the Planck constant is likewise incredibly tiny, measuring in at only 6.626 x 10-34 Joules · seconds. So, to define something else directly from a measurement of this value, insane accuracy is required. This is where the expertise of the National Institute of Standards and Technology (NIST) became a valuable player in establishing the new life of the kilogram.

Bronze weighing dishes from the island of Thera, Santorini, Greece, Minoan civilization, 2000–1500 BC By Norbert Nagel (Own work) [CC BY-SA 3.0 (], via Wikimedia Commons

Bronze weighing dishes from the island of Thera, Santorini, Greece, Minoan civilization, 2000–1500 BC By Norbert Nagel (Own work) [CC BY-SA 3.0 (], via Wikimedia Commons

Weighing in with h

The advanced measurement technology at NIST to be used for the kilogram is called a watt balance and is a modern-day extension of the classic equal arm balance dating back to at least the second century BC. Since it was originally conceived, an unknown mass is visually balanced by placing a collection of known masses on the opposite side of the device. When the two sides are resting at an equal height — i.e., the same force due to gravity, F = mg, is acting on each tray — then it can be assumed that the unknown mass equals the known mass. This millennial-old approach may have even coaxed the human drive to base any definition of mass from a known sample leading to the double-bell jar and platinum cylinder we find locked away today in a suburb of Paris.  

The watt balance sets up a similar arrangement using a comparison of forces. This time, instead of watching gravity do its thing, the device measures electrical and mechanical power, hence the name “watt balance” where watt is the unit of measurement for power (as in 1.21 gigawatts… Great Scott!). Here, a highly controllable measurement of a force resulting from electromagnetism balances the gravitational force on the unknown mass. Flowing a current of electrons through a coil of wire inside a magnetic field on one side of the watt balance will create a force, and if aligned appropriately, this force will shift the two sides into balance for a particular current providing this electrical power.

This initial measurement provides a value of the unknown object’s mass in terms of a current, the magnetic field and the physical dimension of the coil.

Physicist Richard Steiner adjusts the electronic kilogram, an experimental apparatus for defining mass in terms of the basic properties of nature. (NIST)

Physicist Richard Steiner adjusts the electronic kilogram, an experimental apparatus for defining mass in terms of the basic properties of nature. (NIST)

However, we are looking for more: a direct relationship with the tiny and fundamental value of Planck’s constant. So, a second measurement is taken on the exact same setup of coil, alignment, and magnetic field to determine the voltage generated in the circuit when the coil moves through the magnetic field. This is the mechanical power generated during the balancing experiment.

Finally, the math representing these two measurements are merged together giving a relationship between the mass of the unknown object and the current and voltage. Replacing the current and voltage with their “quantum” mathematical versions (via the Josephon effect and the quantum Hall effect), which both contain the fundamental Planck constant, the mass can be directly expressed in terms of h. (If you are interested, check out an overview of the math.)

Historically, this mathematics and experiment on the watt balance has been used with a known mass to accurately calculate the value of h. Flipping the same equation on its head, if a “known” value of h is instead plugged in, then a value for the “unknown” mass, m, may be calculated.

And just with that one mathematical flip, we now have a fundamental definition of the kilogram based on Nature with quantum mechanics being used to describe a macroscopic quantity.

Extreme Accuracy Makes a New Standard

NIST has been building and operating watt balances since the early 1980s in order to nail down our “known” value of h. The latest generation, dubbed NIST-4, began operation in 2015 with specialty modifications to become an international standard for measuring mass. To be a standard, ultimate precision is the goal and NIST-4 is working to master its measurements with an uncertainty to 0.00000003.

The international scientific community is serious about this new definition and there is a deadline to complete all of this work. In late 2014, the International Committee for Weights and Measures (CIPM) established a roadmap of effort toward officially agreeing on the new definition of mass. This plan includes consistent measurements of the Planck constant to within 0.00000005 — placing NIST’s goal into comfortable territory. The end of the road will occur at the 26th Meeting of the General Conference on Weights and Measures (CGPM) in 2018 during which the new unit of mass is expected to be adopted.

Good Accuracy Makes for Extreme Science at Home

This level of extreme accuracy should certainly be left to the extreme scientific national labs such as NIST. However, the foundational idea behind the balance is still one that has been around for centuries. It is with the advancement of our appreciation of the quantum world that we now have mathematics that can relate this type of measurement with one of the most fundamental values representing our Universe, Planck’s constant, h.

So, what if we could now measure — with reasonably good accuracy — h at home? You can … just try building it with LEGO®.

The same team working on the NIST-4 developed a recipe for designing and building an at-home version of the watt balance. For around $400 and with 0.01 (1%) accuracy, masses may be measured at home by using the same technical concept NIST will use in 2018 to provide internationally accepted scientific measurements of the kilogram. The shopping list includes LEGO® (of course), copper wire, off-the-self laser pointers, free data acquisition software, a data acquisition interface (this is the major expense–but you will open up to an enormous new world of experimental opportunities at home!), several permanent magnets, and lots of building and testing fun with the family. 

While this might seem a bit over-the-top for an at-home utility, the same device can also take a known value of a mass and measure the fundamental value of Planck’s constant. Tiny physics with big ideas right in your own basement or garage.

An introduction to the LEGO® watt balance

Watch Video

Table Top Lego Watt Balance from NIST

Now that the idea of building with LEGO® while doing some excellent experimental physics has you ready to jump right in to start ordering parts, you might first get way more in-depth with the NIST efforts to develop the new standard for the kilogram (download article*). Then, go ahead and dive into the instructions for building it all at home, which is included below for your immediate reference.

Chao, L. S., et al. “A LEGO Watt Balance: An apparatus to determine the mass based on the new SI” 
[ download ]


* R. Steiner, E.R. Williams, D.B. Newell and R. Liu. “Towards an electronic kilogram: an improved measurement of the Planck constant and electron mass.” Metrologia. 42 (2005) 431-441. [ download ]


Plutopalooza from Dynamic Patterns ResearchJoin us on Tuesday evening to watch together as the NASA’s New Horizons makes its historic close approach past Pluto. We’ll feature live updates, guides to watching with NASA, and we’ll learn more about what we know and don’t know about our planetary neighbor 3 billion miles away.

↬ The Johns Hopkins University Applied Physics Laboratory and NASA

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Update 8:15:19 PM 07/15/2015:

For our wrap-up of Plutopalooza from DPR — although New Horizons will be bringing much more for many months! — we’ll share this inspiring sequence of images of Pluto from its discovery by humans on February 18, 1930 through our flyby from 7,750 miles away at 31,000 miles per hour on July 14, 2015. ᔥ NASA

Pluto observations through the years

Update 7:59:55 PM 07/14/2015:

New Horizons is locked and data is flowing. “Just like we planned it.” — ‘mom’ from Mission Operations.


New Horizons Locked! 

Update  7:37:52 PM 07/14/2015:

Earlier today, NASA released this false color image of Pluto and Charon — separation not to scale — taken by one of the instruments on board New Horizons. The coloring helps exaggerate the different features on the surface of the planet and its moon to help more clearly identify the various structures. Read more from NASA… 

Pluto and Charon False Color



Update 6:53:01 PM 07/14/2015:

The “phone home” signal from New Horizons is traveling at the speed of light right now… and is over half-home to Earth. We’ll begin streaming the live feed from NASA around 7:15 pm CST right here.

New Horizons phone home half-way home


Update 7:21:23 AM07/14/2015:

NASA released a “sneak peak” image this morning of the latest image taken by New Horizons before it entered into its closest approach routine. Resolution at 4 km per pixel.

Pluto July 14, 2015


Update  06:50:51 07/14/2015:

Good luck New Horizons during closest approach!

New Horizon at Closest Approach


Update 8:16:25 PM 07/13/2015:

In a little over ten hours from now, New Horizons will make its closest approach through the Pluto system. The many scientific instruments on board will begin a carefully orchestrated “dance” that has been pre-programmed and automated to focus on Pluto and Charon. They will cycle through routines to gather as much scientific evidence before the spacecraft zips by. Watch this simulation from NASA stepping through the data collection and then plan to return right here Tuesday evening at 7:15 pm CST to join us as we listen with NASA as they receive the first batch of data from New Horizons.


Update: 3:33:05 PM 07/11/2015
Welcome to Plutopalooza from DPR! We’ll be posting more details and educational information right here and on our Facebook site before the event begins.




A note to the reader: This article requires following special instructions to watch the videos below. It’s also recommended you be on a desktop computer, but if you are on a mobile device (which won’t let you play two videos simultaneously), simply partner with a friend to play the second video.

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There is a long-standing urban legend claiming toilets situated in the Northern Hemisphere flush the draining water with a counter-clockwise rotation, while in the Southern Hemisphere it all spins down clockwise. The Coriolis effect — a real observable effect described by physics — is said to be the culprit. However, if you have experimented with this observation in the past (yes, take a moment to go and check your toilet bowl now), you may have been disappointed to discover just the opposite. You might have tried a different drain and seen even a different rotation in the same house.

Illustration for the Coriolis effect article. A hypothetical situation. The circles are inertia circles. Air mass that is in motion would, if no other forces are present, turn full circle. Credit: Anders Persson

Unfortunately, toilet bowls, sink drains and household bathtubs are too small in scale to allow the effects of the rotation of the Earth to be visible for everyday observation. In fact, if you were standing at the equator, you’d be moving over 1,000 miles per hour, and this rotation speed gets slower as you get closer to each of Earth’s poles. It is this constant rotation, which you don’t even notice, that provides a rotating reference frame for any object moving about the surface of the Earth. Since one full rotation takes 23 hours, 56 minutes, 4.0916 seconds (called a sideral day, per the full rotation of a single spot at the Earth’s surface, whereas the full 24 hour definition is based on the observation of the Sun returning to approximately the same location in the sky), the effect of this rotating frame of reference is quite small on most objects we might observe in our daily lives, like our flushing toilets. On the other hand, physical events on the scale of cyclones clearly demonstrate the clockwise vs counter-clockwise rotations depending on the hemisphere of the storm.

Hurricanes might be incredible to watch on the news, but they are too frightening to experience directly. So, an at home physics experiment was conducted on each half of the world by Destin Sandlin from Smarter Every Day and Dr. Derek Muller from Veritasium, which were cleverly recorded for simultaneous viewing of the results.

Now, here is where the important instructions come in: If you are on a desktop computer, click play on the upper video (occurring in the Northern Hemisphere) and watch for the count down. At just the right moment, click play in the lower video (occurring in the Southern Hemisphere) and watch both videos simultaneously. If you are on a mobile device, have a friend click play on the second video at the end of the countdown. You might also try expanding your desktop web browser to full screen mode (try hitting the key F11) to make sure you can see both clearly. The videos and music are synchronized, so if you don’t think you have them rolling at the same time, reload this page and try again. It will be worth it.

Discover the truth about toilets and see first hand what it really is like to live in a rotating frame of reference (since you probably didn’t realize it before).

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↬ WATCH: The truth about toilet swirls from Science Alert.


Recently, I enjoyed the opportunity to solve and implement a simple web interface problem. The result would not be considered profound or unique by Internet professionals, but nonetheless, it certainly is a powerful application of basic web technologies that allow the seamless flow of information making each of our lives richer and more efficient. Most importantly, I started from scratch and figured out how to do it.

The project was to interface with the FAA live feed of current data and status for airports across the United States and take the user’s airport of choice and instantly present the up-to-the-minute information. I developed a short bit of code, mostly with JavaScript, with a very simplified user interface and completed the project over just a few days, which may be previewed online at the DPR Airport Status page.

Now, I will emphasize, once again, that this project was not revolutionary or particularly complex. However, for my personal skills it was an exciting project to learn techniques and scripting technologies that I have not yet had the opportunity to experiment with before. So, for me, it was new. It was interesting.

The development process did not follow a simple trajectory from starting point A to ending point B. Rather, it was a swirling mess of discovery, error-checking, problem solving, more discovery, more problem solving, and even more problem solving. I fell deep into a pool of experimentation and testing without a clear map of what route to follow. I did not know for certain that I would be able to solve the problem within a reasonable time frame or without a more experienced coder handing me the solution. So, my personal morale sank a bit, yet, I tried to stay focused and dedicated to solving the problem on my own.

Then, in a near sudden moment of clarity or luck — or something — my head reached above the surface of the pool and I discovered the one particular bit of code that would solve the problem. It was a rather satisfying moment.

This rather sloppy process which I experienced is not uncommon in the community of research scientists, both professional and amateur, although not necessarily frequently admitted nor acknowledged. It is a process that can be quite debilitating to many, with constant discouragement and setbacks that might cause one to question their own worthiness to be employed in a scientific field. However, it might be this unnerving and irrational path toward discovery that is the very essence of what is required to stumble upon something new in Nature. Recently, Uri Alon of the Weizmann Institute of Science presented an inspiring talk for TED that links the realization of new ideas to the stumbling through a messy path of discovery that he terms “the cloud.”

While one is fumbling around inside this “cloud” of research, the key element is to remain positive and creative. Prof. Alon takes his own experiences from improvisational theatre and music and connects performance tools from these creative arts directly to the creative processes that occurs inside the research cloud. As Dynamic Patterns Research is a proponent of and an active participant in the mixing of science research, education and outreach with the creative arts, the Alon approach of creative cloud scientific research is quite inspiring to our own interests. Even with the simple coding project of creating the Airport Status interface, this experience was a creative opportunity. Here, the developing of the underlying code resulted in a presentation of interactive art: a creative process that other people can play with and respond.

Taking a random walk through any creative process, from science research, code development, performance art to the written word or the integration of all of these expressions — and having the confidence to do so — should not be a scary or disappointing approach to progress, but one that is embraced, encouraged, and even required for discovery.




Last updated February 16, 2018