The story where I saw this calls the phenomenon “ground resonance”. While it looks and acts a lot like an unbalanced washing machine in the spin cycle, which doesn’t seem like a resonance phenomenon, from what I understand this can be caused by a shock to the system from landing, and the helicopter is susceptible at certain rotor speeds. If the compensation is 180ยบ out of phase with the wobble you get positive feedback, so it makes sense that this could happen; you’d either want to speed up or slow down the rotor, were it safe and easy to do so, to change the feedback. But this happened pretty quickly.
Daily Archives: February 28, 2012
This Might Be On the Test
In an advanced physics class.
Ice Sliding Off a Bowl: When Does It Leave the Surface?
A small block of ice is placed on the top of an inverted spherical bowl. The ice is then given a slight nudge so that is slides down the side of the bowl. At some point, the ice will speed up enough to leave the bowl. At what angle does this happen?
That's a Big Twinkie
How Big a Battery Would It Take to Power All of the U.S.?
Generating capacity is, however, only one side of the story. Storage systems are rated not only by their power, or how fast they can crank out energy (measured in gigawatts), but also by the total amount of energy they store (measured in gigawatt-hours). A facility with an energy capacity of one-gigawatt that can only supply electricity for 10 minutes would not be very helpful; in an ideal world it could do so for, say, 100 hours, thus storing 100 gigawatt-hours. Building up new pumped hydro-facilities similar to existing ones would probably help in all but the most disastrously long of wind lulls. For those worst-case scenarios, we might still have to brace for rolling blackouts.
Of course, this simple calculation also assumes current consumption levels. How would we power all those electric cars that we’re supposed to be driving in the future?