Gravity is the pulling force that holds objects to the surface of a planet. Beyond Earth's atmosphere, the planet's gravity force grows weaker. The space shuttle, for instance, experiences only a tiny pull, called microgravity. It's strong enough to keep the shuttle in Earth's orbit, yet weak enough that objects inside the shuttle have almost no weight. So they float in space.
Nothing works quite the same in microgravity as it does on Earth.
Blood doesn't flow through the body in the same way. Carrots grow in U-shapes instead of growing straight down. And candle flames turn into blue balls of fire. By studying the effects of microgravity, scientists believe they will better understand many processes that occur on Earth. In microgravity, crystals grow bigger and more perfectly than on Earth.