Title text:

Reductio ad absurdum fails when reality is absurd.

Transcript:

At the left, a teacher is holding a pointer, pointing at a picture on the screen.]

[The picture shows a hydraulic lift, with a small fluid vessel on the left connected to a tube at the bottom, which connects to a large vessel on the right. On top of the large vessel is a weight labeled 1000 and a Cueball. The fluid in the large vessel is labeled with an upward arrow. Megan’s hand is over the small vessel, with a downward arrow indicating that she’s pressing on it.]

[Cueball, Hairbun, and Blondie are sitting at school desks going right to left.]

Cueball: No, that can’t be right.

Cueball: If hydrostatic pressure worked that way, then you could use it to make machines that exert near-infinite force.

Cueball: And ancient people could have demolished entire mountains just by drilling small tunnels and filling them with water.

[Caption below comic:]

When I first learned about Pascal’s law, I tried to disprove it by showing that it would lead to absurd consequences, but it turns out hydraulic presses and ruina montium are both real things.

Source: https://xkcd.com/3087/

explainxkcd for #3087