It was another fine Fourth, not Bradbury-esque as in last year's nostalgia-fest, but up close to the action as I attended a full-scale fireworks display. They were set off in a field belonging to a big neighborhood high school less than a mile from my home. It was a perfect, balmy, cloudless evening, and I sat with the multitude to enjoy a half hour of pure joy. The hazy sky was filled with brilliance and blast and showers of sparks and rainbow colors, the kindest of explosions. Modern inventions lit up the crowd like the fireflies that now fill the forests: glowing plastic light-tubes (I believe they use the same biochemicals as the fireflies do), little screens of cell phones and digital cameras, and even the briefly green-lit dial of my digital watch. Children spun the light tubes in patterns, making elaborate mathematical diagrams out of persistence of vision. And then, once I returned to my neighborhood, there were more fireworks, this time small fire-fountains permitted, on this one night, for use in the driveways and yards.

If there needs to be any more proof that I am now truly a geek, my appreciation of fireworks is it. I kept on thinking of the skyrockets rising up against the force of gravity, against 32 feet per second², until the upward force is spent and it reaches the top of its trajectory, at which point it explodes and fills the sky with brilliance. What a way to reach zero velocity! Some of the burning fragments kept going, and I could see them trace over the top of the parabola before they burnt out. The chemical explosions add their own momentum, sending the fragments out with much more momentum than the rocket which brought them, but these too are subject to the pull of gravity, thus creating the glorious downdrift of sparks, creating willows and waterfalls of golden fire. I thought about gravity and momentum as I exclaimed over the fireworks. Meanwhile, behind me, another spectator discussed her cholesterol measurements loudly as the rockets soared and blasted away.

I have finished my introduction to momentum, gravity, orbits, Kepler's laws, and other basic material from Chapter 4. I will return to them in due time. Meanwhile, it's on to another very relevant subject: parabolic trajectories for objects shot out at an angle (rather than vertically, as with fireworks). I never know when I might be called on to man the artillery and besiege a stronghold. In the rockets' red glare, the light is still there.

Posted at 2:35 am | link