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NIST physicists build a watt balance using LEGO blocks to measure Planck's constant
From phys.org:
[center]
CAD model of the LEGO watt balance. The balance pivots about the T-block at the center. Two PVC endcaps with copper windings hang from universal joints off either side of the balance beam. Coil A is on the left and Coil B is on the right. A 10 gram mass sits on the Coil A mass pan and each coil is concentric to its own magnet system. Two lasers are used to calibrate and measure the linear velocity of each coil. Credit: arXiv:1412.1699 <physics.ins-det>[/center]
[hr]
(Phys.org)—A team of physicists at the National Institute of Standards and Technology (NIST) outside of Washington D.C. has found a way to bring physics to the masses—they've designed and built a watt balance based on LEGO blocks. They've also written a paper and uploaded it to the preprint server arXiv in which they describe their device and how it was built it, should readers wish to construct one of their own.
To understand why the team at NIST would do such a thing requires a bit of background. Over the last century or so, scientists have been slowly replacing physical artifacts used for measurement, with devices that are based on more standard phenomenon—the meter, for example, is now based on time, rather than a rod sitting in a building. The lone holdout has been the kilogram, which is still defined by a chunk of metal sitting in a vault in France. But that's going to change soon, as the International System of Units is reviewing possibilities—one of which are devices based on measuring the value of Planck's constant to a certain degree of accuracy. Planck's constant describes the relationship between the energy and frequency of an electromagnetic wave. One kind of device that can be used to measure mass based on Planck's constant or taken the other way, to find a value for Planck's constant based on a known mass, is called a watt balance. It does its work by balancing the force exerted by gravity with the force of current in a coil—the mass of an object can be calculated by comparing the mechanical power to the electrical power in the device.
more ...
CAD model of the LEGO watt balance. The balance pivots about the T-block at the center. Two PVC endcaps with copper windings hang from universal joints off either side of the balance beam. Coil A is on the left and Coil B is on the right. A 10 gram mass sits on the Coil A mass pan and each coil is concentric to its own magnet system. Two lasers are used to calibrate and measure the linear velocity of each coil. Credit: arXiv:1412.1699 <physics.ins-det>[/center]
[hr]
(Phys.org)—A team of physicists at the National Institute of Standards and Technology (NIST) outside of Washington D.C. has found a way to bring physics to the masses—they've designed and built a watt balance based on LEGO blocks. They've also written a paper and uploaded it to the preprint server arXiv in which they describe their device and how it was built it, should readers wish to construct one of their own.
To understand why the team at NIST would do such a thing requires a bit of background. Over the last century or so, scientists have been slowly replacing physical artifacts used for measurement, with devices that are based on more standard phenomenon—the meter, for example, is now based on time, rather than a rod sitting in a building. The lone holdout has been the kilogram, which is still defined by a chunk of metal sitting in a vault in France. But that's going to change soon, as the International System of Units is reviewing possibilities—one of which are devices based on measuring the value of Planck's constant to a certain degree of accuracy. Planck's constant describes the relationship between the energy and frequency of an electromagnetic wave. One kind of device that can be used to measure mass based on Planck's constant or taken the other way, to find a value for Planck's constant based on a known mass, is called a watt balance. It does its work by balancing the force exerted by gravity with the force of current in a coil—the mass of an object can be calculated by comparing the mechanical power to the electrical power in the device.
more ...
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