Gravity is one of the four fundamental physical forces. The other three forces are the electro-magnetic force, the weak nuclear binding force and the strong nuclear binding force.
Gravity affects all physical, chemical and biological processes on Earth.
After all, it is gravity which forces the Moon to fly around the Earth and keeps the Earth on an orbit around the Sun. Gravity is responsible for various phenomena, in particular thermal convection, buoyancy, hydrostatic pressure and sedimentation. This allows us, for instance, to shape a metallic part by pouring a melt into a mould, to separate lighter from heavier constituents through sedimentation or for the transport of fluids. The effects of gravity can be undesirable if we want to understand certain physical, chemical or biological phenoma or study the complex interaction of different forces involved in a process, for example, in liquids and gases. Gravity can mask our view on the full set of parameters that influence a physical, chemical or biological process.