Who doesn't love roller-coasters? Tianna and Sammy could spend days on them! They love the way their stomachs jump into their throats, making it feel like they're floating. That feeling is weightlessness, which is kind of like what astronauts feel in space. Astronauts call it microgravity, because during the fall, they feel only a tiny amount of gravity's pull. Tianna and Sammy wondered: how do ordinary things behave in microgravity?