Weightless – Part 10 (Draft)


(Continued from Part 9 Draft)

“Now’s my chance.” Morris sat in his adjustable chair in his office on the second floor. On his desk there was a computer, a bronze elk, several text books, a green engineers notepad, a football team banner, his log book and a calculator. Adjacent to his desk, a nice bookshelf filled with literature and engineering textbooks.

“I know the box sled concept is the best way to go, but to satisfy Ellen and Mr. Torres, I’ll analyze all practical phenomenon related to mass and prove it.“ He grabbed his pen and notepad. “The most obvious is Newton’s 2nd Law, F=ma, where the acceleration of a mass is proportional to the net force applied to it.”

Newtons2ndLaw

 

Looking up at the ceiling for a moment he put down his pen and thought, “I wonder… Is there any direct way to measure mass?” After a moment he looked back down.

Morris searched his physics, dynamics, and other engineering texts books hard copy and online for relationships associated with an objects mass.

There was a knock at his door, “Morris, could you use some help?”

Morris didn’t really want help but he was learning from experience that two heads were better than one as long as no one dominated. “Oh, Dr. Best?”

“Please, call me Ellen.”

“Yah, a, come on in. I was just getting started.”

“She’ll want the credit,” he thought.

“I’m sorry we got off to a bad start,” Ellen said. “I’m impressed that you started a prototype on your own.”

“My son thinks,” Morris said,  “it’s interesting that his dad does science projects in the garage.”

“Oh? How old’s your son?”

“He’s twelve.”

“Really? I have a twelve year old also.”

“So, tell me if you like this analysis approach. Let’s brainstorm all the ways in which mass can be measured either directly or indirectly.”

“Perfect,” Ellen said. “Shall I write down the ideas on the board as we identify them?”

“You bet.” Morris pointed at the tray under the board. “I hope one of those markers still works.”

Ellen put her computer on the small desk and took her place at the board, dividing the board up into 6 equal squares with perfect lines.

“Okay,” Morris said as he thought how organized Ellen was. “Let’s get the general principles listed, and then we can take turns describing how each might be utilized in measuring mass in a weightless environment. Let’s start with the concept favored by Mr. Torres. Essentially, you have a mass oscillating back and forth on a spring, or multiple springs in this case. The spiderweb support systems simply serves to keep the container from floating off in some arbitrary direction, but I think the web causes many dynamic problems.”

“Too many degrees of freedom,” Ellen agreed.

“Right. The radial strings also act like additional springs. And there’s nothing in his design to keep the box from rotating or twisting back and forth like the pendulum on my grandfather clock.”

Morris thumbed through a text book and found the equation. “Here it is. A mass on a spring oscillates with a natural frequency proportional to the square root of ‘k’ over ‘m,’ where ‘k’ represents the spring mechanical properties and ‘m’ is the mass of the object.

Ellen wrote omega = sqrt(k/m) on the board and labeled it Spiderweb Spring-Mass-Oscillation frequency.

NaturalFrequency

 

 

Morris observed, “A variation on Mr. Torres’ concept would be to replace the web with a linear rail and bearing system to guide the box. This is similar to my concept, but I’m not using oscillations to determine the mass.”

“Before we get to your concept,” Ellen suggested, “lets describe this and every variation in more detail. For example, what is the stimulus or perturbation. If I understand correctly, the operator or some other actuation mechanism moves the load off-center and releases. The frequency of oscillation is proportional to the spring coefficient and the mass…”

“Very good,” Morris admitted. “Now it’s your turn.

“She’s good,” Morris thought.

(To be continued)

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