During the USMP series, scientists studied all three crystal formations by melting metals in furnaces and cooling them at different rates. On Earth, gravity causes flows in the melted metal that affect crystal formation. In microgravity, these flows are eliminated, and scientists can observe and control the solidification process better. With the clues they gather in space, scientists can improve the quality of metals produced on Earth. The force of Earth's gravity extends far into space.
Weight is the force with which a body is attracted to the Earth.
Any object in a state of freefall experiences microgravity, or near weightlessness. An orbiting spacecraft is actually falling around the Earth. The spacecraft's altitude and speed cause its fall to match the curvature of the Earth, so that it never hits the Earth but continually orbits the planet. All objects carried by an orbiting spacecraft are also in a state of freefall.