Clean Air for the Space Station - Life support systems on the Station must supply oxygen and remove contaminants in the Station's air. The Station must provide clean water for the crew. The weight of our body depends on how hard gravity pulls on us. Some of the other planets in our Solar System are bigger than Earth, and some are smaller. How much you would weigh on a planet depends on the planet's size.
Gravity is a force everywhere, but sometimes scientists want to do studies without gravity's pull.
We can make things weightless for a short time by dropping them a tall tower. We can make them weightless for longer times in a spacecraft orbiting around the Earth. They can see what happens when gravity is absent from a process, such as the growth of animal or plant cells.