Definition of gravity

the force that attracts a body toward the center of the earth, or toward any other physical body having mass.

Explanation:

the force that pulls us back to earth when anything goes up

so it pretty much means

whatever goes up always comes down

Explanation:

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.