Translation to aid those who do not know Chinese.
Why does Snowball get bigger as it rolls?
First, we have to know that snow is water in solid form. When the snowball is rolling, the ground that is in contact with the snowball will melt first due to pressure, then it will form into ice. This ice, in turn, will stick onto the snowball.
In science, this is due to the molecules bonding to itself as it rolls. Hence, when this process is repeated – rolling, pressing, melting, freezing, the snowball will just get bigger and bigger as it rolls!
Source: Quoted from an educational book