Question

why is it difficult to walk on snow

Answer 1

 Friction is that property which oppose movement of one object over other. 
* It is of two types,static and kinetic. Moving objects exert kinetic friction. 
* friction is measured by a quantity called coefficient of friction. 
> Snow has lower coefficient of kinetic friction. Thats why it allows the objects to move over it easily. 
* Friction is a atomic or molecular property. 
* It s based on newton's third law. 
* friction in liquids is called viscosity

Answer 2

snow is consider as solid matter . hence ,when we place our foot in snow it goes inside.while removing our foot from snow it gets difficult because snow holds tightly .
so ,friction is the reason