Question

We can easily walk with flat shoes on sand why??

Answer 1

there is friction on sand which helps us to walk with flat shoes. and it's because ,in case of flat shoes , area of contact is larger than area of contact on sand and hence they do not high heel shoes.thus flat shoes exerts less pressure sink in the sand but high heel shoes do sink.
hope it helps !

Answer 2

we can easily walk with flat shoes on sand as well as icy places because it decreases the pressure put on a particular area and less pressure to put on comparatively large area