Wednesday, October 10, 2012

"It's not rocket science"

Sierra gets ready to launch her group's rocket.
Click on any photo to enlarge.

What goes up, must come down!

The instructor switches to the triggered launcher. Sam is holding on to the mast, which is threatening to fall over in the breeze.

Raising the mast at the start of class.
Lecture instructor Janet Preston is closest to the camera in the center.

"It's not rocket science, you know."

How many times have you heard that saying? And what do you think people mean by it?

Usually they mean that a task or an idea isn't very hard to learn.

But rocket science itself is not particularly hard to learn, at least to begin.

A rocket is defined as a vehicle whose thrust is derived solely from the mass and velocity of its propellants. The basic idea in rocket propulsion is that of Newton's Third Law, "[f]or every action there is an equal and opposite reaction."

Funnily enough, this is the only one of Newton's Laws that survived into 21st century American science language more or less as Newton originally stated it and as I learned it in Tapton School's 1970s physics classes.

Not that us British schoolkids learned them in the original Latin. Far from it. In the schools of darkest Sheffield city, in the depths of the socialist period, attending the city's best science school, we took no Latin, or at least very little.

But we were fairly serious about anything to do with engineering, and so we learned the more or less traditional English phrasing of all three Newton's Laws.

Call me a traditionalist, but I think them easier to learn and to apply:

Newton's First Law: An object at rest will remain at rest, and an object in motion will remain in motion, in a straight line with constant speed, unless acted upon by an outside force.

Newton's Second Law: Force is proportional to mass times acceleration.

Newtons Third Law: For every action, there is an equal and opposite reaction.

So, real so-called "rocket science", if it is anything at all,  is primarily the application of these laws.

Students in PS 2003 Physics Lab learned how to apply Newton's Laws by launching water rockets during Week Four. Water rockets are made using soda or pop bottles and a launcher made from PVC pipe. You can get instructions for their manufacture from NASA, no less.

Ours had a twelve volt compressor salvaged from a vehicular emergency battery pack whose battery had expired. Although this rig was prone to overheating, having the electric compressor made it easy to use, saving the hours of hand pumping normally required for these experiments.

I made the launcher at home and briefly demonstrated it during Week Three's lab at the end of the period. Students went away with group tasks to complete for Week Four:

All groups: design and build a rocket to test. Vary nose cone, fins, shape, size
Group 1: Figure out a way to measure the final altitude of a rocket using triangulation
Group 2: Figure out a way to measure the final altitude of a rocket using slow motion video
Group 3: Figure out a way to find the optimum mass of water, keeping air pressure constant
Group 4: Figure out a way to find the optimum air pressure, keeping water mass constant

Of the groups, I would say Group 3 had the hardest job. They had to make a new launcher with a trigger, since the original launcher was designed to just released the rocket when the air pressure from the compressor overcame the friction on the launcher tube.

They came up with a handy-dandy trigger mechanism involving electrician's tape, a part of a pop bottle and cable ties that worked very well, (and indeed at the end of the class I stored their launcher away carefully for next time).

Each group had to collect data and write up their results as a formal lab report.

Now that's what I call rocket science!

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