An iPad filled with apps weighs more than one with nothing installed


Photo: Apple
An iPad filled with apps weighs more.

Which weighs more? An iPad filled with media and apps, or an iPad with no media or apps installed?

It sounds like a trick question — the digital age equivalent of “What weighs more, a pound of feathers or a pound of rocks?”

But surprisingly, an iPad without anything installed on it does weigh less than an iPad that is full.

Why? Because data stored on flash drives has weight. The difference is almost infinitesimally minute, but it is there.

The extra weight comes from flash storage storing more data in memory. The transistors in flash memory distinguish between a 1 and a 0 by trapping electrons.

The more data a flash drive stores on it, the more electrons are trapped. And these electrons do have weight: For 4GB of data, the difference between full and empty is 10-18 grams. For a 64GB iPad, it would be 12 times that.

These calculations were done back in 2011 by University of California at Berkeley professor of computer science John D. Kubiatowicz for Amazon’s Kindle e-reader, but they’d be applicable to any device with a flash drive.

And here’s another fun fact: An iPad with a fully charged battery weighs more than an iPad with a dead battery.

If you start feeling your muscles strain when carrying an iPad that is almost full, though, it’s probably all in your head. Even the most sensitive scales have a resolution of only 10 –9 grams. Your arms definitely can’t feel it.

Source: New York Times

  • Ephraim Vishniac

    This smells like horseshit, especially the bit about the battery.

    The calculation assumes that “empty” memory is cleared to all zeroes, which is not necessarily so. The content of disused storage can be anything at all. And while trapped electrons make the difference between a zero and a one, it’s all not necessarily the case that trapped electrons = 1 and no trapped electrons = 0. Do those trapped electrons come from outside your device? I don’t know, but that doesn’t seem right.

    A charged battery has more charge separation than a discharged one, not more electrons. Electrons flow from one side of the battery, through your device, to the other side of the battery as it discharges, but they don’t leave the device. The total number of electrons doesn’t change.

  • W.S.R.

    Hmmm…. This is only true if in a completely sealed dust free environment. The iPad with no data or apps could easily weigh more… IF a tiny spec of dust lands on it.
    That would make the counting of extra electrons completely redundant..
    Hey, here’s an idea… let’s not post this kinda BS on a supposedly informative news blog site.

  • I would sooner attribute the extra weight to oils from your fingers deposited by installing all that stuff.

  • I never knew, only iPad used Flash storage and battery ..

    Using dump headline and content to get visitors attention. :Crap:

  • digitaldumdum

    “Because data stored on flash drives has weight. The difference is almost infinitesimally minute, but it is there.”

    Utter nonsense. Ridiculous! It’s the BS in this “article” what weighs a lot… most heavily on the unsuspecting reader’s mind. If Cult is trying to be like The Onion, success! If not, gazing for hours at one’s own navel is surely more interesting than this “article.”

  • Stephen Agnew

    I call BS. The iPad doesn’t bring into it’s system more electrons when storing more data, it only uses the electrons that are already there. So wether or not it is storing 64GB or 5GB, the same amount of electrons are in the iPad, just in a different location.

    • Ulrik Nyman

      I completely agree. Maybe the original analysis was of only the flash memory and this could actually have stored electrons from the battery thus moving weight from battery to flash memory.

      I am not sure if even this part is true.

  • Electrony

    The part about the battery is definitely wrong. The electrons don’t disappear from the battery, they are still there but cannot be used anymore.

  • Andrew Skelland

    LMAO all the comments saying this is BS, as the article states the tests were conducted by a Computer Science PhD professor within one of the best universities in the world.

    Am pretty sure they aware of all the factors that you have stated.

    This was also reported on back in 2011 by The New York Times,

    Might want to do some research yourselves.

    • Craig

      It wasn’t a test, it was a calculation. While a memory circuit may, in theory, weigh slightly more depending on the data stored within, the iPad will not. The electrons in the iPad are in a closed system. They merely change positions.

  • subtorious

    Loved it. I’m a software/electrical engineer, and I’ve never considered weight added by electrons before.

    But I must disagree with your last sentence: “Your arms definitely can’t feel it.” [10-18 grams]

    From my
    experience with cannabis, I know that I can feel the difference in
    weight between a 3.5gram bag and a 7gram bag (an eighth and a quarter
    ounce respectively).

    So I conclude, without any experimentation, that tens of grams are human perceptible. :)

    Thank for a great article.

    • Ulrik Nyman

      But 10^-18 grams is 0.0000000000000000001 grams

      • Subtorious

        Ah, that does make more sense. I was reading it 10 to 18 grams not 10 raised to the negative 18th power.

  • JSintheStates

    I was going to say, “Nonsense”, until one of the commentors started name dropping UC, Berkeley. So, Utter F#@king Nonsense! 1s and 0s are not atomic filing cabinets with electrons in them! Your Berkeley Prof has a Haight Ashbury problem!

  • Jeffrey Chard

    I suspect the good professor may have done the calculations on 1 April.
    Memory works on displacement of charge, the device will remain electrically neutral so there is no new electrons.
    A iPad that may have additional mass if it has a higher energy state (resulting for the stored charge). The additional mass = (increase stored energy ) /c squared.
    0.1 watt additional energy = 10 -18 kg
    I am not familiar with the electronics in an iPad. I am uncertain whether a memory bit with a lower energy state is a 1 or 0.
    There is no doubt a fully charged ipad would weigh more than a fully discharged ipad.

  • Eric

    To keep things in perspective, mind the 10-18 scale…

    “Kubiatowicz had responded to the question “When an e-reader is loaded with thousands of books, does it gain any weight?” in the New York Times late last month. “In principle, the answer is yes,” he said, “[but] the amount is very small, on the order of an atogram [10-18 grams]. This amount is effectively unmeasurable.”

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