2012-11-28
Explanation
This comic presents a physics problem as a trick to get the reader to unknowingly perform a crude calculation. At the top, it displays the equations: 5ml(1e-3 kg/ml) * 12.5 m/s = P and P = 80 kg * v, with the instruction "Solve for v." It looks like a straightforward conservation of momentum problem, and the comic pauses to ask "(Did you do it?)" before revealing the punchline.
At the bottom of the comic, after a large blank space designed to give the reader time to work it out, the text reveals: "Congratulations. You know how much speed a man in space would gain by ejaculating." The values given (5ml at a density of 1e-3 kg/ml at 12.5 m/s, with a person massing 80 kg) are real-ish estimates for the relevant quantities, and the conservation of momentum equation is the correct physics for computing the resulting velocity change. The humor lies in tricking the scientifically-minded reader into earnestly solving what turns out to be a deeply juvenile problem.
The votey panel adds a preemptive note: "Before you write me, the rocket equation does not apply due to your negligible semen-mass." This anticipates the pedantic objection that, technically, since the person loses mass in the process, the Tsiolkovsky rocket equation should be used rather than simple momentum conservation. Weiner dismisses this by noting that the mass expelled is negligible compared to body mass, making the simpler equation a perfectly adequate approximation.