On Earth, when we cry, our tears fall down our faces due to gravity. Gravity is the force that pulls objects toward the center of the Earth. This is why tears stream down your cheeks rather than floating around your eyes.
In space, astronauts experience what we call microgravity - a condition where the pull of gravity is greatly reduced. The International Space Station orbits Earth in a state of continuous free fall, creating a weightless environment. Without significant gravity to pull them down, tears don't stream down an astronaut's face when they cry.
In the microgravity environment of space, surface tension becomes the dominant force acting on liquids like tears. Surface tension is caused by the cohesive forces between liquid molecules pulling inward. This creates a natural tendency for liquids to form spherical shapes that minimize surface area. Instead of falling down, tears cling to surfaces like the eye or skin, forming blobs or bubbles. The water molecules in tears are strongly attracted to each other, causing the tear to maintain its shape rather than streaming down.
In space, astronauts need to be careful with their tears. Since tears don't fall, they can accumulate and form large water blobs that cling to the face or even float away. These floating water blobs can be problematic in the space station environment. They might drift into sensitive equipment, causing electrical shorts or other damage. Astronauts typically use tissues or towels to absorb tears before they become an issue. This is just one of many adaptations astronauts make to deal with the unique challenges of living in microgravity.
To summarize what we've learned: On Earth, gravity pulls tears downward, causing them to stream down our faces when we cry. In the microgravity environment of space, this gravitational pull is greatly reduced. Without significant gravity, surface tension becomes the dominant force acting on liquids like tears. Instead of falling, tears form blobs that cling to the eye and face due to surface tension and cohesion. Astronauts must be careful to wipe away tears before they become floating water blobs that could potentially damage sensitive equipment.