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

Feb 3, 2016

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 ($\left(2 \text{ lb.")/("sq.in.}\right)$)

Suppose a man weighing $200 \text{ lb.}$ has feet, each of which covers a surface area of $30 \text{ sq.in.}$

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

for an average pressure of
$\textcolor{w h i t e}{\text{XXX")(200 " lb.")/(60 " sq.in.") ~~ (3.3 " lb.")/("sq.in.}}$

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

A camel weighing $600 \text{ lb.}$ has $4$ feet, each of which might cover an area of $100 \text{ sq.in}$.

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

for an average pressure of
$\textcolor{w h i t e}{\text{XXX")(600 " lb.")/(400 " sq.in.")=(1.5 " lb.")/("sq.in.}}$

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