Question

Why can camels walk on top of sand but humans can not?

Answer 1

Relative to their respective masses, camels have proportionally more foot area than humans.

Explanation:

Warning: None of the values I'm using are likely to be accurate; they are simply for demonstration. (I don't have a camel conveniently handy to weigh or measure its foot size).

Suppose sand can support `2` pounds of pressure per square inch (`(2 " lb.")/("sq.in.")`)

Suppose a man weighing `200 " lb."` has feet, each of which covers a surface area of `30 " sq.in."`

with both feet on the ground, the man's `200 " lb."` of weight will be distributed over an area of
`color(white)("XXX")2xx30 " sq.in." = 60 " sq.in."`

for an average pressure of
`color(white)("XXX")(200 " lb.")/(60 " sq.in.") ~~ (3.3 " lb.")/("sq.in.")`

Since this is greater than the amount of pressure sand can support,
the man will sink.

A camel weighing `600 " lb."` has `4` feet, each of which might cover an area of `100 " sq.in"`.

With all four feet on the ground, the camel's `600 " lb."` of weight will be distributed over an area of
`color(white)("XXX")4xx100 " sq.in." = 400 " sq.in."`

for an average pressure of
`color(white)("XXX")(600 " lb.")/(400 " sq.in.")=(1.5 " lb.")/("sq.in.")`

Since this is less than the amount of pressure sand can support,
the camel will not sink.