Featured Research

from universities, journals, and other organizations

Kilogram Is Losing Weight: Redefine Kilogram Based On Universal Constants, Scientists Urge

Date:
March 1, 2008
Source:
DOE/Sandia National Laboratories
Summary:
The kilogram is losing weight and many scientists agree that it's time to redefine it. They are hoping to redefine the kilogram by basing it on standards of universal constants rather than on an artifact standard. "The idea is to replace the single master kilogram with something based on physical constants, rather than an artifact that could be damaged accidentally," says one mechanical engineer.

Hy Tran examines a kilogram sample in a mass comparator at Sandia's Primary Standards Laboratory.
Credit: Photo by Randy Montoya

The kilogram is losing weight and many international scientists, including some at Sandia National Laboratories, agree that it’s time to redefine it. Scientists are hoping to redefine the kilogram by basing it on standards of universal constants rather than on an artifact standard.

The International Prototype Kilogram (IPK) or “Le Grand K,” made in the 1880s, is a bar of platinum-iridium alloy kept in a vault near Paris. “The idea is to replace the single master kilogram with something based on physical constants, rather than an artifact that could be damaged accidentally,” says mechanical engineer Hy Tran, a project leader at the Primary Standards Laboratory (PSL) at Sandia.

Of the seven units of measurement in the International System, or SI, the kilogram is the only base still defined by a physical object. In addition, copies of the kilogram have changed over time by either gaining or losing weight as compared to the standard kilogram.

The purpose of redefining the kilogram is based on risk reduction, says Tran. “In the long term, the redefinition — especially if performed correctly — is beneficial because of risk reduction and because it may enable better measurements in the future,” he says.

By replacing the master kilogram — Le Grand K —with a unit based on physical constants, researchers at multiple laboratories and at national measurement institutes could establish traceability, he says.

Tran says the kilogram will remain the kilogram; it’s only the way it will be defined that will change. He says the earliest the kilogram would be redefined is 2011.

“If and when the redefinition takes place, it will be done in such a fashion as to have minimal or no practical impact with other measured quantities,” Tran says. “In other words, if it is redefined so as to ensure better than 10 parts per billion agreement — rather than 20 parts per billion agreement — then we will see no major changes immediately.”

Based on the current formal definition of the kilogram (the mass of the 1 kilogram prototype) and experimental dissemination to standards labs, the uncertainty (95 percent confidence) in PSL’s kilogram is about 40 parts per billion, compared to the IPK.

One part per billion is about the ratio of the area of a square 3/32 inch on a side, with respect to the area of a regulation NFL football field (including the endzones, or 120 yards by 53-1/3 yards), Tran says.

The target originally proposed by the Bureau International des Poids et Mesures (International Bureau of Weights & Measures) was to get one of the alternative kilogram definitions, such as the experimental measurement of force on the watt balance (or counting atoms on the silicon sphere), and deriving the kilogram, matched to experimental measurements of the prototype kilogram to within 20 parts per billion.

Sandia physicist Harold Parks agrees that the redefinition of the kilogram is inevitable and says there are a couple of issues that need to be resolved before it’s redefined.

“The watt balance method of defining the kilogram makes the most sense for those of us in electrical metrology and so far it is the most accurate,” he says. “But other proposals, such as those based on counting the number of atoms in a silicon crystal, are being considered.”

The watt balance is based on an idea that compares electrical and mechanical power with a high degree of accuracy, he says.

Conflicts between the results of the watt balance and the atom counting experiments will also need to be resolved, Parks says.

“The NIST (National Institute of Standards and Technology) watt balance experiment has achieved the accuracy needed to redefine the kilogram, but the experiment will need to be confirmed by other groups in order for the results to be fully accepted,” he says.

Tran says redefining the kilogram will have little impact on the Primary Standards Lab or the broader nuclear weapons complex. The lab develops and maintains primary standards traceable to national standards and calibrates and certifies customer reference standards.

“It should not affect PSL or the complex if the international metrology community ensures that they fully consider the uncertainties, the necessary experimental apparatus to realize the kilogram, and implementation issues prior to agreeing to the redefinition,” Tran says.

In preparation for the change, PSL staff members are staying up to date in research in metrology and standards practices. Staff also participate in standards activities in order to ensure that any transition would be smooth.


Story Source:

The above story is based on materials provided by DOE/Sandia National Laboratories. Note: Materials may be edited for content and length.


Cite This Page:

DOE/Sandia National Laboratories. "Kilogram Is Losing Weight: Redefine Kilogram Based On Universal Constants, Scientists Urge." ScienceDaily. ScienceDaily, 1 March 2008. <www.sciencedaily.com/releases/2008/02/080228120943.htm>.
DOE/Sandia National Laboratories. (2008, March 1). Kilogram Is Losing Weight: Redefine Kilogram Based On Universal Constants, Scientists Urge. ScienceDaily. Retrieved August 20, 2014 from www.sciencedaily.com/releases/2008/02/080228120943.htm
DOE/Sandia National Laboratories. "Kilogram Is Losing Weight: Redefine Kilogram Based On Universal Constants, Scientists Urge." ScienceDaily. www.sciencedaily.com/releases/2008/02/080228120943.htm (accessed August 20, 2014).

Share This




More Matter & Energy News

Wednesday, August 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Awesome New Camouflage Sheet Was Inspired By Octopus Skin

Awesome New Camouflage Sheet Was Inspired By Octopus Skin

Newsy (Aug. 19, 2014) — Scientists have developed a new device that mimics the way octopuses blend in with their surroundings to hide from dangerous predators. Video provided by Newsy
Powered by NewsLook.com
Researcher Testing on-Field Concussion Scanners

Researcher Testing on-Field Concussion Scanners

AP (Aug. 19, 2014) — Four Texas high school football programs are trying out an experimental system designed to diagnose concussions on the field. The technology is in response to growing concern over head trauma in America's most watched sport. (Aug. 19) Video provided by AP
Powered by NewsLook.com
Green Power Blooms as Japan Unveils 'hydrangea Solar Cell'

Green Power Blooms as Japan Unveils 'hydrangea Solar Cell'

AFP (Aug. 19, 2014) — A solar cell that resembles a flower is offering a new take on green energy in Japan, where one scientist is searching for renewables that look good. Duration: 01:29 Video provided by AFP
Powered by NewsLook.com
Tiny Satellites, Like The One Tossed From ISS, On The Rise

Tiny Satellites, Like The One Tossed From ISS, On The Rise

Newsy (Aug. 18, 2014) — The Chasqui I, hand-delivered into orbit by a Russian cosmonaut, is one of hundreds of small satellites set to go up in the next few years. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins