Weightless – Part 6


(Continued from Part 5 – These are first drafts of a work in progress)

Gregory held a nut with an open wrench inside the box while his father tightened the bolt under the box.

“What are these metal things you’re attaching to the bottom of the box?”

“They are pillow block bearings. I’m making a way for this box to move freely along these rails, like a roller coaster on rails.” Mr. Jackson pointed to two long round rods under the box. “The box will slide along these rails on these low friction linear ball bearings attached to the wooden box.”

Mr. Jackson continued to talk while they worked together to tighten the remaining nuts and bolts. “I think this is a much more compact solution for the space craft. Of course the final product wouldn’t be made out of wood.”

The engineer and his apprentice moved from one bolt to the next tightening each one.

“Another engineer wanted to hang the box from wires, like a playground swing, and then attached the front and back of the box to springs. By pushing on the box and letting it oscillate back and forth, you get a measure of the weight of the box and rocks.”

Mr. Jackson looked up at Gregory.

“But without gravity…” Gregory stopped. “In free-fall, won’t the swing just float up towards the swing wires attached to it?”

“Well, their idea was to have three or four wires attached to the box pulling in mostly opposite directions like the main radial fibers of a spider web. Then attach two springs pulling the box in a perpendicular direction into and away from the web.”

Gregory squinted.

Mr. Jackson put his wrench down and grabbed his engineering notebook and opened to a blank page. He drew a picture of a box held by four wires attached radially outward from the box with the other end of each wire attached to the spacecraft walls.

“It does look like a spider web,” Gregory said.

“Not very compact, is it?” Mr. Jackson said. Can you imaging being an astronaut trying to maneuver from one end of the capsule to another avoiding this web?”

He then drew two springs on opposite sides of the box to pull the box in and out of the plane of the four wires.

“Have you ever seen this equation?” Mr. Jackson said as he wrote a mathematical relationship on the paper.

Gregory shook his head.

“The oscillation of a mass on a spring can be modeled like this.”

f = (1/[2*π])*√(2k/m)

“See, look at this.” Mr. Jackson turned the book so Gregory could see the illustration and equation upright. “The frequency or rate of oscillation ‘f’ is proportional to the mass ‘m’, and the properties of the spring. The properties of the spring are in this ‘k’ value.” Mr. Jackson pointed at each term as he explained. “If we measure the frequency, and we know the ‘k’ value, we can solve for ‘m’ and determine the mass.”

Mr. Jackson paused while Gregory studied the equation and the picture. “Notice that ‘m’ is in the denominator. This means that for larger mass, the frequency will be smaller.”

“So, did they build it?”

(To be continued)

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