Later, they studied YouTube videos of the same. This allowed them to create a mathematical model of urinary systems — a model showing that mammals take the same time to empty their bladders despite considerable differences in the size of their bladders — differences in volume than can range from 100 mL to 100 L.

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New Scientist explains what's going on:

According to the team's model, an animal's size does make a difference to urination time – but only very slightly. Their law of urination says that the time a mammal takes to empty a full bladder is proportional to the animal's mass raised to the power of a sixth, meaning even very large changes in mass have little effect on the time.

There are limits to this scaling. Gravity only plays a small role in the urination of very small mammals like rats and bats, which urinate in under a second. Instead, viscosity and surface tension dominate, which explains why their urine is released as a stream of individual drops rather than the continuous jet seen in larger mammals.

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You can check out the entire study at the preprint archive arXiv: "Law of Urination: all mammals empty their bladders over the same duration."

Top image: An elephant on a toilet, origin unknown.