main article image
Smarter Every Day

Here's The Science-Backed Way to Poop Without Splashback

The fluid dynamics of a stealthy dump.

13 AUG 2015

The whole purpose of YouTube channel Smarter Every Day is to change ordinary people's lives by making them, well, smarter. But we have to admit that after years of watching, the video that's changed our lives the most is probably this one, on the fluid dynamics of poop. Because who hasn't struggled with the sound, mess, and occasional embarrassment caused by toilet splashback? Well, you don't have to anymore, because science has a solution.


As you've probably figured out if you've ever spent time dropping objects into water, the poop splash is caused when your poop displaces water, and forms a cavity of air in the fluid at the bottom of your toilet bowl. All that air has nowhere to go, and so the discontinuity in pressure causes the water to slap back together.

It's that slapping back together that sends water shooting up out of the bowl, and depending on the size, shape, and angle of your poop, it can produce some pretty impressive jets. As Destin shows with his oddly realistic faecal models in the video above, if your poop hits the water at an angle, as most do, it can produce a water jet higher than the original drop height - which means that, yes, your bum is about to get wet. 

But it's not so much the type of poop that influences the size of the splashback, it's the size of the cavity it forms in the water. And interestingly, small, round poops that drop straight down into the water actually produce the biggest voids, and accordingly, the biggest splashback. You can see all these experiments performed in slow motion in the video above.

So how do you fix the problem? Well it really all comes down to the surface tension of water, which is calculated by force per unit length. With open water, such as a toilet bowl, surface tension makes the water molecules at the surface 'stick' together, almost like a film. Which means that when something is dropped onto the surface of the water, this outer film pushes down, forming a void around the object. And as we've learnt, that void produces splashback.

All you need to do to avoid this splash is simply alter the surface tension of the water. Which sounds like it might be tricky, but it actually just involves one simple and easy-to-access tool - toilet paper. Watch the episode of Smarter Every Day above to find out how, and have your life changed forever. Thank you, science.

More From ScienceAlert