However, since the Space Station and everything in it are essentially in free-fall, the force of gravity is essentially not sensed. There are however minor accelerations which result from atmospheric drag on the Station and the fact is that only one point on the Station is exactly in free-fall. All other locations are close to but not exactly in free-fall. Gravity keeps the Earth in its orbit around the sun. Gravity keeps the Earth's atmosphere, oceans, and inhabitants from drifting into space.
Gravity pulls the rain to the rivers, and ultimately to the sea.
Gravity guides the development and growth of plants and affects the way our bones and muscles develop and function. Gravity controls the fluid in our inner ear, giving us a sense of direction and the ability to balance. The specific mechanisms used by plant and animal cells, tissues, and organs to sense gravity is not fully understood. Some scientists believe that the lack of gravitational acceleration could have adverse effects on the health of astronauts in long-duration missions. Some scientists believe that observing the effects of low gravity levels on living systems may help them understand how such systems work in and out of gravitational fields.