On the USML missions, scientists explored how candle flames extinguish, how insulated wire smolders, and how drops of fuel burn in low gravity. Microgravity provides scientists with a truer picture of the influence of forces like surface tension, which is always present but is often hidden by the stronger force of gravity. During the two USML missions, a furnace was used to melt and cool various metals. On the shuttle, the melted metals are not affected by flows caused by gravity. 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.