How do you measure big forces accurately? By calibrating your force transducer on the world’s biggest weight – 1,000,000 pounds of force. This machine ensures planes don’t break apart, jets provide required thrust, and rockets make it to their destination.
Thanks to the people at NIST for showing me around: Rick Seifarth and Ben Stein.Animations here are by Sean Kelley and additional footage by Jennifer Lauren Lee.
Before visiting NIST in Washington DC I had no idea machines like this existed. Surely there’s an accurate way to measure forces without creating such a huge known force?! Nope. This appears to be the best way, with a stack of 20 x 50,000 lb masses creating a maximum force of 4.45 MN or 1,000,000 pounds of force.
I also wouldn’t have thought about all the corrections that need applying – for example buoyancy subtracts about 125 pounds from the weight of the stack. Plus the local gravitational field strength must be taken into account. And, the gravitational field varies below grade. All of this must be taken into account in order to limit uncertainty to just five parts per million (.0005%).