Melted metals will first form crystals wherever the melt touches the container. This contact influences the structure of the solid metal and what properties it will have. During the MSL missions, scientists will use the microgravity conditions to levitate, or lift, materials in order to process them without a container. The substance will form crystals at the same rate throughout the sample because there are no container walls. 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.