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  • An apple weighs about 1 newton, the world record for jet engine thrust is 570,000 newtons.

  • And the Saturn V rocket that launched people to the moon had a thrust of 33,360,000 newtons

  • But how can we measure forces this big accurately?

  • Well, we need to ask this guy.

  • Hi my name is Rick Seifarth I'm a physical scientist in the Mass and Force Group.

  • Am I supposed to look at the camera?

  • Sure.

  • Okay.

  • You can look at anything you like.

  • Rick manages a dead weight machine that can apply 4,448,222 newtons.

  • Why such a strange number? Because that's exactly equal to 1,000,000 pounds of force.

  • There are twenty fifty thousand pound increments in this machine

  • 20 times 50 equals 1,000,000 pounds.

  • Cumulatively that's 4.45 mega newton.

  • Elsewhere in the world, are there larger masses that people have calibrated?

  • I ask that question to every visitor we get and I've not gotten..

  • one response that says: yeah I know where bigger stuff is calibrated.

  • So if I really want to go out on a limb and brag I'll say

  • these are the largest mass objects ever calibrated.

  • Anywhere

  • The machine works like this, below ground are the 20 carefully calibrated masses.

  • Their weight is used to calibrate force sensors also called

  • Force Transducers, in the lab upstairs.

  • This is a one million pound capacity 4.45 mega newton,

  • and this is 13.3 mega newtons, three million pounds force.

  • This is the biggest machine of it's type in the world, and obviously one of a kind.

  • One of these,

  • will be placed on the compression head right here.

  • Then, a hydraulic ram in the attic starts to raise the green lifting frame

  • And once the force transducer contacts the red loading frame,

  • well then it starts lifting the weights downstairs.

  • And as the lifting frame continues to rise, more and more of the

  • 50,000 pound weights become suspended by the force sensor.

  • And since the weights create an accurately-known force,

  • the readouts from the force transducer can be precisely calibrated.

  • These devices are then sent out into the field.

  • Well literally, there's a test stand that's set up with one of these gizmos-

  • a force transducers - embedded in the test stand somewhere.

  • And so the rocket is fired up, perhaps ramped up, ramped down and those forces are monitored.

  • You know, in the old movies you'd hear: "go to 104% of power." Well, how do they know it's 104% of power?

  • Because somebody's measured it somewhere.

  • When it comes to minimizing uncertainty, these guys aren't messing around.

  • This piece right here is approximately 50,036.27 pounds of mass.

  • Approximately.

  • Approximately, yes! [laughter]

  • Think about that for a moment.

  • Each of these pieces has a mass equivalent to ten minivans,

  • and their exact value is known to within several American nickels.

  • Just a few American nickels worth of difference?

  • Yeah.

  • That tiny uncertainty is measured with respect to the very definition of the kilogram

  • using K20 - that's the United States fundamental mass standard.

  • This is done by comparing combinations of known weights, starting with K20, with larger unknown weights,

  • gradually working up to larger and larger masses.

  • For example, here a single 5-kilogram mass is compared to two 2s and a 1.

  • At some point in this process, they convert and start working in pounds, going from 50-pound masses to 500 pounds,

  • and then 2500 pounds. And then, using a scale in the floor, to reach 10,000 pounds and then 20,000,

  • and finally 30,000 pounds.

  • Combinations of these huge weights are then used to calibrate the 50,000-pound masses which form the weight stack.

  • And we have to have that, because what we sell is the vertical force vector that's generated by these weights

  • hanging in a gravitational field. We sell that with an uncertainty attached to it of 0.0005%,

  • five parts per million, so that means at full one million pounds of applied force, we guarantee that to be accurate - if you will -

  • within five pounds.

  • Not only does that mean the masses have to be accurately calibrated,

  • it also means the gravitational acceleration at this location has to be taken into account.

  • It's actually slightly less than Earth's standard gravity, so an additional 600 pounds are required.

  • Plus, the buoyant force must be counteracted,

  • since these masses displace 125 pounds of air,

  • a further 125 pounds must be added to reach a million pounds of force.

  • What strikes me as kind of amazing is that, like, this machine needs to exist, in a way.

  • When I would have thought about it, like how would Boeing measure its forces, I would have thought

  • OK, they just, you know, calibrate a device that works up to X but then they can, you know,

  • generalize. Well, generalize - you know what I mean, like - Yes!

  • There's an axiom that says "one physical test is worth a thousand expert opinions."

  • And that has proven itself time and again, particularly in the world of physical testing.

  • If you're getting on an airplane that somebody has built, are you willing to accept a 10% uncertainty on these numbers

  • or do you want it to be - the uncertainty on these measurements to be down in the mud?

An apple weighs about 1 newton, the world record for jet engine thrust is 570,000 newtons.

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World's Heaviest Weight

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    林宜悉 posted on 2020/03/28
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