How can a balloon take off?
To make a balloon lift off, the buoyancy of the balloon in the air is greater than its own gravity. The condition of increasing buoyancy is to increase the volume of the balloon under the maximum condition, and the measure of reducing gravity is to fill the sphere with less dense gases, such as hydrogen and helium (hydrogen density: 0.0892 g/L; Helium density: 0.1786g/l)