This is from a book on physics for kids. What do you think ert means?

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  • It turns out the "ert" part of "inertia" is actually from Latin ars (art), and in fact "art" is descended from ars as well! Oct 20, 2015 at 15:36

2 Answers 2


I read that panel similarly to the way Patrick Stevens did, just with another extra level of punning.

"Whatever ERT is, I'm in it!"

  1. The literal reading (which is from the character's point of view), "I'm in ERT, whatever ERT is," i.e., I don't know what ERT is, but whatever it is, I'm in, I buy it, I buy the idea.

  2. The funny meaning (which is from the writer's point of view, and of course, this is what the writer wants the panel to convey, IMHO),

"I'm in it" = "I'm in ERT" = "I'm inert."

And because I (the character) am so inert, I'm still in my bed!
(Note: someone who is inert does nothing when they should be taking action.)

  • 1
    As an introduction to the idea of inertia I find it rather presumptuous that the author would expect the reader to be familiar with the term "inert" and its relationship to the concept of "inertia", so it might not be the best joke, but your answer definitely explains it :) Sep 27, 2015 at 19:15
  • Just for clarity, the puns in children's text books are supposed to be very unfunny, I believe that there is an international law on the subject. Sep 28, 2015 at 10:36

The word "inert" means roughly "unchanging", "does not interact with other things". The word "ert" doesn't really exist, but is used as a pun. It has a more common use (still very uncommon) and a less common use; this is the less common use.

  1. The more common use: "ert" can be used to mean "not inert" or "has the property that it reacts with other things". This is only used in a physics-related context, and is only used to compare something with a previously mentioned inert thing. The word "inert" has to have been used recently so that people will recognise that "ert" is meant to be derived from "inert".
  2. The less common use, and the one in your cartoon: the premise is that the person in bed doesn't know what "inert" means, and has parsed the word as "in ert", much as one might be "in Spain" or "in bed". They don't know what an ert is (and they have good reason not to, because the word doesn't actually exist), but they are claiming to be "in it" anyway. This makes the comic panel a little… comic… because we understand that the person in bed is just bluffing. (It's not a very good joke.)

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