The photo shows astronauts training in a NASA plane that flies in a parabolic arc--the same path a projectile follows--so they can experience free fall, just as they will in space. To find out what these flights are like, check out the Reduced Gravity: Vomit Comet Blog from the American Physical Society's Physics Central. To learn about gravity in space, see the first page of Fluids in Space, also from Physics Central, and What is Microgravity? (but don't be fooled by the title--there is plenty of gravity in space around the Earth, and it keeps satellites in their orbits).
