WEBVTT - How Do Scales Measure Weight?

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<v Speaker 1>Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff,

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<v Speaker 1>Lauren Bogelbaum. Here, there's something so commonplace about a weighing

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<v Speaker 1>device that it's easy to forget its deeper significance, as

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<v Speaker 1>these slightly skewed spring scale in any local produce aisle

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<v Speaker 1>reminds us. The scale has long served humans as the

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<v Speaker 1>chief arbiter of commerce, the maker or breaker of shipping

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<v Speaker 1>budgets and carry on capacity, and the utility player of

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<v Speaker 1>the pharmaceutical bench. From the smallest, most fine tuned laboratory

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<v Speaker 1>balance to the pit and girder monsters that weigh train

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<v Speaker 1>cars and tractor trailers, scales make modern life possible. Scales,

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<v Speaker 1>or more specifically, balances weighed heavily on the minds of

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<v Speaker 1>ancient builders, inventors, and economic advisors. Too. Small balance weights

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<v Speaker 1>dating back to around five to six thousand years ago

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<v Speaker 1>provide some of the first hints of mankind evolving grasp

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<v Speaker 1>of science and mathematics. The most basic surviving balance from

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<v Speaker 1>Egypt predates the Dynastic period, placing its construction at earlier

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<v Speaker 1>than three thousand BCE. Like us, the ancient Egyptians applied

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<v Speaker 1>scales both in trade and in a saying ores and

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<v Speaker 1>alloys balances way an object by matching it against one

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<v Speaker 1>or more reference weights. They have a delicate touch and

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<v Speaker 1>are still used in laboratories. Scales use somewhat different physical

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<v Speaker 1>principles and mechanical components to measure weight in other forces.

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<v Speaker 1>Spring scales, for example, measure weight using Hook's law, by

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<v Speaker 1>which you can relate in objects weight to the stretching

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<v Speaker 1>or compression of a spring made from a given material.

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<v Speaker 1>Not all scales use springs, but all do measure weight

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<v Speaker 1>using mechanical components, So mechanical and digital scales differ only

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<v Speaker 1>in how they display that weight, mechanically like with a

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<v Speaker 1>needle on a dial, for example, or electronically alike with

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<v Speaker 1>an LED display. In a latter case, the scale employs

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<v Speaker 1>an analog to digital converter that translates the continuous readout

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<v Speaker 1>data from the scale into discrete digital information, much in

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<v Speaker 1>the same way that an MP three encoding scheme digitizes

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<v Speaker 1>the waveforms of music. An internal CPU converts the data

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<v Speaker 1>into input for a display board, which then shows the

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<v Speaker 1>result on a digital screen. Generally speaking, digital scales require

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<v Speaker 1>less expertise to use than those with mechanical readouts and

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<v Speaker 1>are capable of higher precision and faster processing. Still, the

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<v Speaker 1>capabilities of specific devices vary, particularly when the weights are

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<v Speaker 1>measured in tons. But let's talk more about those different

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<v Speaker 1>mechanical components that let us measure weight with scales. Think

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<v Speaker 1>of how a roadside carjack might lift a car via

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<v Speaker 1>mechanical adage the leverage of a handle or the inclined

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<v Speaker 1>plane of a screw, or how a car mechanic's hoist

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<v Speaker 1>might use hydraulic pressure in the same way. Different types

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<v Speaker 1>of scales weigh objects using a variety of operational principles,

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<v Speaker 1>like hydraulics, pneumatics, or bending beans. Scales come in all shapes, sizes,

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<v Speaker 1>and configurations, but the basic component doing the measuring is

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<v Speaker 1>nearly always a load cell. A load cell is a

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<v Speaker 1>kind of transducer, which is a term for a device

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<v Speaker 1>that converts one form of energy into another. Through load cells,

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<v Speaker 1>digital scales change mechanical energy the smooshing caused by a

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<v Speaker 1>sitting load or the stretching caused by a hanging load,

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<v Speaker 1>into an electrical effect. The widely used strain gage, for example,

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<v Speaker 1>reads compression or tension as tiny changes in electrical resistance

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<v Speaker 1>in what's called a whitstone bridge. Let's break that down

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<v Speaker 1>using a compression strain gauge as an example. Okay, Compression

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<v Speaker 1>occurs when an applied force reduces an object's volume, but

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<v Speaker 1>it can also refer to a more general decrease in

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<v Speaker 1>size along one or more dimensions. As it happens, squishing,

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<v Speaker 1>an electrically conductive material changes its electrical resistance because longer

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<v Speaker 1>and narrower wires are more electrically resistant than shorter and

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<v Speaker 1>wider wires. Think of it like water pumping through a pipe.

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<v Speaker 1>The longer and narrower the pipe, the harder it will

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<v Speaker 1>be to force water through it. Now, different materials experience

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<v Speaker 1>different changes in resistance during compression, a quality known as

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<v Speaker 1>gauge factor. A gauge factor can also alter in response

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<v Speaker 1>to temperature. The go to material for strain measurements is

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<v Speaker 1>called constantine alloy. It's usually fifty five percent copper and

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<v Speaker 1>forty five percent nickel, and it performs well at the

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<v Speaker 1>range temperatures that humans are comfortable at. To detect the

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<v Speaker 1>change in resistance caused by weight compression, one or more

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<v Speaker 1>strain gages are placed within what's called a whitstone bridge.

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<v Speaker 1>A whitstone bridge is an electrical circuit that can detect

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<v Speaker 1>an unknown electrical resistance by balancing it against known resistances

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<v Speaker 1>elsewhere in the circuit. In a sense, it's like a

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<v Speaker 1>balance scale for electrical resistance. The weight of the resistance

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<v Speaker 1>on one side tells you the unknown weight of the

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<v Speaker 1>resistance on the other. Strain gauges are the most widely

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<v Speaker 1>used type of load cell, but they're not the only one.

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<v Speaker 1>After all, research, industry, and commerce require the capacity to

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<v Speaker 1>measure weights under a seemingly limitless variety of environmental conditions

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<v Speaker 1>and space constraints, while also controlling for possible errors. Industries

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<v Speaker 1>that require greater safety and sterility often turn into pneumatic

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<v Speaker 1>load cells, which derive the weight of an object by

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<v Speaker 1>measuring the air pressure necessary to balance it. These blowhards

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<v Speaker 1>work well in the food industry and at hazardous sites

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<v Speaker 1>because they don't contain fluids that might seep, drip, or

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<v Speaker 1>spurt into the environment. Pneumatic cells can have a wide

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<v Speaker 1>range of weights with high accuracy, but they require a clean,

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<v Speaker 1>dry atmosphere and tend to take their sweet time responding

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<v Speaker 1>Hydraulic load cells, which measure load as a change in

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<v Speaker 1>fluid pressure are commonly found weighing tanks, bins, and hoppers.

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<v Speaker 1>Because they function without electricity, Hydraulic cells work well in

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<v Speaker 1>out of the way locals where power is a ify prospect.

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<v Speaker 1>They're pricey and complicated, but rugged they can handle million

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<v Speaker 1>pound loads. Load cells also come in all kinds of

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<v Speaker 1>different sizes, shapes, configurations, and materials, so that you can

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<v Speaker 1>use scales in different environments for different jobs. If you

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<v Speaker 1>need to take measurements in a wet environment, you can

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<v Speaker 1>opt for a hermetically sealed canister cell. If you're in

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<v Speaker 1>a facility concerned with height clearance issues, you can use

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<v Speaker 1>a thinner bending beam cell. And if you're expecting to

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<v Speaker 1>deal with extraneous forces affecting the load cell, say you're

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<v Speaker 1>using scales in a moving vehicle, in deep water or

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<v Speaker 1>on an aircraft, an s beam load cell that uses

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<v Speaker 1>a zigzag design can help control for that. Measuring force

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<v Speaker 1>is as fraught with technical troubles as any precision measurement,

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<v Speaker 1>which is no minor matter when one considers that piles

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<v Speaker 1>of money, and more importantly, human lives can rest on

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<v Speaker 1>the difference of a few grams. Researchers develop all kinds

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<v Speaker 1>of technologies to help make scales dependable in real world circumstances.

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<v Speaker 1>No matter the well scale, these devices could range from

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<v Speaker 1>being accurate in laboratory settings to highway weight enforcement and beyond.

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<v Speaker 1>On the larger end, scales employ levers to convert extra

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<v Speaker 1>large forces into manageable ones. Thus, the load cells in

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<v Speaker 1>some large truck scales only need to be able to

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<v Speaker 1>measure a fraction of the total weight, and thus can

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<v Speaker 1>easily handle between fifty to one hundred thousand pounds, which

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<v Speaker 1>is around twenty five to forty five thousand kilos, which

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<v Speaker 1>is a lot either way. And remember how Hook's law

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<v Speaker 1>helps you more or less accurately weigh your fruit and

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<v Speaker 1>vegetables on the spring scale at the grocery store. It

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<v Speaker 1>also underlies the operation of one of the smallest force

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<v Speaker 1>measuring devices in the world, the atomic force microscope, used

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<v Speaker 1>in biochemistry, biology, and materials engineering. Such microscopes use a

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<v Speaker 1>micron scale silicon or silicon nitride cantilever, which is a

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<v Speaker 1>spring like beam supported only on one side to detect

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<v Speaker 1>nano Neewton and peak Newton tugs forces on the scale

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<v Speaker 1>of intermolecular attractions. Today's episode is based on the article

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<v Speaker 1>how digital scales work on HowStuffWorks dot Com, written by

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<v Speaker 1>Nicholas Jerbis. Brain Stuff is production of by Heart Radio

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<v Speaker 1>in partnership with HowStuffWorks dot Com and is produced by

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<v Speaker 1>Tyler Klang. For more podcasts from my heart Radio, visit

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<v Speaker 1>the iHeartRadio app, Apple Podcasts, or wherever you listen to

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<v Speaker 1>your favorite shows.