SCIENCE

The Tears of an Astronaut
In space, no one can hear you scream. But can they hear you cry? In this new video, Canadian Space Agency Astronaut Chris Hadfield demonstrates the physics of tears in space.

Discussion Ideas:

• The final words spoken by Chris Hadfield, the astronaut in the video, are “It’s gravity.” Actually, it’s surface tension in zero-gravity! Can students explain how a lack of gravity prevents tears from falling in space?
  • Let Matt Voss, a chemist who answers some of the Department of Energy’s “Ask a Scientist” questions, explain it: “Since water is normally affected by gravity, it will find the lowest point in any container . . . This can be a bottle, or if that bottle has a hole in it, then the floor. Under zero-gravity, however, there is no gravity to hold the water in bottom of the container. Therefore it will float around . . . The water will still be cohesive with itself, for the most part, meaning that you won’t ever get a fine mist of water without a lot of work.”
• Hadfield explains that tears won’t fall in space—they just cling to your face. How do students think astronauts deal with other bodily fluids in space—how do they go to the bathroom?
  • Toilets in space actually function a lot like toilets on Earth—except they use powerful air vacuums to empty themselves, since gravity will not take the waste away.
• So toilets and teardrops need to be modified for life in zero gravity. So does exercise equipment! Watch the video in our “media spotlight,” “Space Gym.” Can students explain how engineers had to modify everyday gym machines for life in space?
  • Astronauts must “strap in” to equipment such as treadmills or stationary bikes so they don’t float away.
  • Astronaut “weightlifting” equipment is actually weightless! Astronauts build muscles using pressurized air to create resistance.
• Chris Hadfield is an experienced astronaut—he was the first Canadian to do a spacewalk! Hadfield’s background is in aviation (he is a former test pilot) and engineering. What job skills do students think astronauts need?
  • Astronauts need to have math and science skills! NASA requires all astronaut candidates to have degrees in engineering, biological science, physical science, or mathematics.
  • Astronauts need to be healthy! NASA requires astronauts to pass a rigorous “space physical.” The physical measures a candidates’ strength, dexterity, and endurance. Watch our video “media spotlight” video on NASA’s “Space Gym,” where astronauts use out-of-this-world equipment to stay in shape.
  • All astronauts need to have excellent vision and stand at least 1.5 meters (4.9 feet) tall.
  • Most astronauts have military backgrounds, because until recently most space programs (such as the Canadian Space Agency or NASA) were funded by governments. This is changing, as private companies such as Mojave Aerospace Ventures and Virgin Galactic invest in spaceflight.
• Hadfield is a man who knows where is towel is. Have any students read Douglas Adams’ popular cult novel The Hitchhiker’s Guide to the Galaxy? (Commenters on Hadfield’s YouTube video clearly have.) Why is this relevant?
  • One of the most famous concepts from the book is that a towel “is about the most massively useful thing an interstellar hitchhiker can have.” In addition to all the sci-fi hazards Adams lists (avoiding the gaze of the Ravenous Bugblatter Beast of Traal, for instance), towels can also dry your tears.