NASA released last week an incredibly awesome high-resolution video of astronauts aboard the International Space Station playing around with tiny little globs of water.

The video shows Scott Kelly (the man currently on a year-long mission to study the effects of long-term life in space on the human body) adding food coloring and an antacid tablet to the delicate sphere of liquid floating around.

Activities like this aren’t just for kicks. NASA uses high-resolution images and videos like this to help in scientific experiments conducted onboard the ISS, allowing researchers on the ground to better evaluate what they’re seeing.

The video itself underscores the tendency of water to form spheres in zero-gravity environments. There’s a whole book one could write about the physics of water, but the simple answer is that surface tension — a key trait of water — keeps the droplets together and causes them to gather up in the smallest possible area and volume it can. In this case, that’s a sphere.

(Of course, that same water, if you were to dump it outside in a deathly cold vacuum environment, would violently boil first due to the drop in pressure, then immediately freeze because of the temperature. We’re still waiting for that video, NASA!)

ESA astronaut André Kuipers plays with a drop of water on the International Space Station during his 2012 six-month Promisse mission.
Photos via NASA/ESA, Screenshot from YouTube