From: veritasium
Measuring exceptionally large forces, such as the 570,000 Newtons of a world-record jet engine thrust or the 33,360,000 Newtons of a Saturn V rocket, requires extreme accuracy and specialized equipment [00:00:00]. To achieve this precision, factors like gravity and buoyancy must be meticulously accounted for.
The World’s Largest Force Calibration Machine
Rick Seifarth, a physical scientist in the Mass and Force Group, manages a unique “dead weight machine” designed for calibrating massive forces [00:00:20]. This machine can apply 4,448,222 Newtons, which is precisely equivalent to 1,000,000 pounds of force [00:00:28]. It consists of twenty 50,000-pound increments, cumulatively reaching 4.45 meganewtons [00:00:41]. Rick Seifarth suggests these are likely the largest mass objects ever calibrated anywhere in the world [00:00:56]. Another, larger machine is also mentioned, with a capacity of 13.3 meganewtons (three million pounds force), described as the biggest of its type in the world and one-of-a-kind [00:01:26].
Precision in Mass Calibration
The machine utilizes 20 carefully calibrated masses located below ground, whose combined weight is used to calibrate force sensors, also known as force transducers, in the lab above [00:01:08]. As a hydraulic ram raises a lifting frame, the force transducer contacts a loading frame, gradually suspending more and more of the 50,000-pound weights [00:01:39]. Because the force exerted by these weights is accurately known, the force transducers can be precisely calibrated [00:01:59].
The level of precision is extraordinary; for example, one of the 50,000-pound masses is known to be approximately 50,036.27 pounds [00:02:39]. This exact value is known to within the equivalent of several American nickels, despite each piece having a mass equivalent to ten minivans [00:02:50]. This tiny uncertainty is maintained relative to the fundamental definition of the kilogram, using K20, the United States’ fundamental mass standard [00:03:03]. The process involves comparing combinations of known weights, starting with K20, and gradually working up to larger masses, converting to pounds at higher increments (50, 500, 2500, 10,000, 20,000, and 30,000 pounds) before finally calibrating the 50,000-pound stack [00:03:13].
The vertical force vector generated by these weights is guaranteed to have an uncertainty of 0.0005% (five parts per million) [00:03:50]. This means that at a full one million pounds of applied force, the accuracy is guaranteed to be within five pounds [00:04:04].
Accounting for Gravity and Buoyancy
Achieving such precision necessitates accounting for environmental factors:
- Gravitational Acceleration: The gravitational acceleration at the machine’s location must be taken into account [00:04:16]. It is slightly less than Earth’s standard gravity, requiring an additional 600 pounds to be added to the physical masses to achieve the desired force [00:04:21].
- Buoyant Force: The buoyant force exerted by the air on the masses must also be counteracted [00:04:26]. Since the large masses displace 125 pounds of air, a further 125 pounds must be added to the stack to accurately reach a million pounds of force [00:04:29].
Importance of Physical Testing
The existence of such a machine highlights the critical need for direct physical testing rather than relying solely on generalization or theoretical models [00:04:39]. An axiom states that “one physical test is worth a thousand expert opinions,” especially in the realm of physical testing [00:04:58]. For applications like aircraft manufacturing, the uncertainty on these force measurements must be driven “down in the mud” to ensure safety and reliability [00:05:10].