The gas (helium) in the hydrogen balloon will change the sound! This is because the sound wave of sound must propagate through the medium, and the type, state and density of the medium will affect the propagation speed of sound wave. Human voice usually travels through the air. When the composition of air changes from 78% nitrogen and 265,438+0% oxygen to 80% helium and 20% oxygen, the density becomes one-third of that of normal air, and the speed of sound propagation is nearly three times faster because of this change, so the voice of people who inhale helium will become higher. This interesting phenomenon makes people who inhale helium scream and breathe. Helium is an inert gas, which is non-flammable, non-toxic, non-radioactive, naturally occurring and harmless to the environment. It is also the second most abundant substance in the universe besides hydrogen. However, its stock on the earth is very scarce. In the United States, helium is extracted from natural gas wells and radioactive stones. Radioactive stone mines will release a non-radioactive by-product-helium in the process of disintegration for hundreds of millions of years. Helium will gather in natural gas wells, be developed together with natural gas, and then be separated. Helium is widely used in medical treatment.