Follow Slashdot blog updates by subscribing to our blog RSS feed


Forgot your password?

"Ballooning" Spiders Use Electrostatic Forces To Generate Lift 213

KentuckyFC writes "Many types of small spider release threads into the air which then lift and carry them significant distances. Biologists have found them at altitudes of up to 4 km. The conventional thinking is that the threads catch thermal air currents which then carry them away but this does not explain how spiders perform their trick even when there is little or no wind. Now one physicist says the explanation is the atmosphere's natural electric field which has an average downward-pointing magnitude of 120 Volts per metre. He calculates that a strand of silk need only gain a negative charge of around 30 nanoCoulombs to lift a spider. That explains how the spiders take off on windless days, how they reach such great heights and how several strands can lift heavier spiders of up to 100 milligrams."
This discussion has been archived. No new comments can be posted.

"Ballooning" Spiders Use Electrostatic Forces To Generate Lift

Comments Filter:
  • Re:Yes, But... (Score:4, Informative)

    by deusmetallum ( 1607059 ) on Monday September 23, 2013 @10:34AM (#44923825)
    He lives in New York, he's always swung from the multitude of high rises.
  • Re:batman (Score:5, Informative)

    by MickyTheIdiot ( 1032226 ) on Monday September 23, 2013 @10:51AM (#44923935) Homepage Journal

    The bat signal itself doesn't fit with physics.

    My parents have owned a searchlight rental business for 30 years now. For the first Batman movie they were asked to put a bat signal cutout on the searchlight to simulate the bat signal. The thing is that searchlights have too high a candlepower and the light just bends around the cutout. The light spreads more the farther away from the searchlight. It looks cool when shown against a wall, but far out in the sky it simply doesn't work. The physics of light doesn't allow it.

  • by necro81 ( 917438 ) on Monday September 23, 2013 @11:15AM (#44924135) Journal
    The earth's magnetic field is almost certainly unrelated. The magnetic field is generated internally due to us having a molten iron core. This atmospheric electrical field comes from the bulk transport, separation, and friction of huge air masses - like the kind that give rise to thunderstorms. There's interplay between the two, especially during a solar storm (e.g., aurorae), but you couldn't freeze the magnetic field by tapping the atmosphere.

    As for why we can't tap that, I could only speculate. 120 V/m sounds like a sizable field - strong enough that we ought to be able to feel it. On the other hand, the E-field in an ordinary capacitor is many orders of magnitude greater (10s of volts, perhaps, but separated by just microns). You can get a greater E-field from peeling scotch tape off its roll.

    Also bear in mind that an electric field, by itself, is not a store of energy. In order to make use of that field, you need to have charge traverse that field - a flow of electrons. If we think of the atmosphere between stratosphere and ground like a giant capacitor, its stored energy is 1/2 * C * V^2. The V term might be very large (120 kV/km, squared!), but if the C is tiny, then you end up without much energy. And do not conflate power and energy: you can get quite a spark from a discharging capacitor (or a lightning bolt!) - great instantaneous power - but it doesn't last. Unless there's some source to continuously replenish the charge separation, you may not be able to tap much energy. I suspect that the available energy is very diffuse; more diffuse than, say, the kinetic energy of wind that we are able to capture with turbines. You would probably need kilometer-sized antenna arrays to capture much useful power.
  • by jones_supa ( 887896 ) on Monday September 23, 2013 @12:44PM (#44925215)

    I've just read that one bolt of lightning powers one household with all their energy needs for a month. I'm not too sure how accurate that is; but I think we'll need a lot more than that.

    I will try to plug the numbers in. Let's see how this goes.

    According to the toast power article [], a lightning packs "over five billion joules of energy". I will round that down to 5 billion. A watt is the same thing as "joules per second". A month has 60 * 60 * 24 * 30 = 2,592,000 seconds. Then, 5 * 10^9 J / 2,592,000 s = 1929 J/s. This means that we can run the house at a constant power consumption of 1929 watts. Converted to a standard kWh number that would be 1389kWh per month.

    That's pretty much on the spot. It would indeed be enough to run a house of a small family for one month, accounting electrical heating running around winter.

  • by Anonymous Coward on Monday September 23, 2013 @01:54PM (#44926001)

    Easy: it's not a dipole. The spiders are expected to carry a net charge.

Behind every great computer sits a skinny little geek.