# Q & A: Snow Shoes

Q:
Why does snow shoes enable a person to walk on deep snow?
- Anonymous (age 14)
James Weldon Johnson College Preparetory Middle School, Jack
A:
Have you ever tried cutting an apple with your finger, by pressing down on it? Impossible, right. Why?

The reason is that your finger applies the pressure over a relatively large area on the surface of the apple. So instead of cleanly cutting it, you eventually crush the apple's surface or do nothing (depending on the age/type of apple, etc).

The same idea applies to snow shoes, in reverse.

When you walk in snow with your normal, foot sized shoes, your weight is distributed only along the length and width of your shoe, so the pressure on the snow is high and you sink into it.

What if there was a way to decrease the pressure?

What is pressure? That's the first question.

Pressure is defined as force/unit area. Force in this case is the force of gravity on you. That's:

F = ma = (your mass in kg) * (9.81 m/s^2)

The area is whatever the area of the contact surface is. (the area on the bottom of your shoe).

So our only 2 options if we are going to decrease pressure is to either decrease your mass or increase the area on the bottom of your foot.

We can't decrease your mass enough to get this effect. We have to increase the area. Look at your snow shoes. They are very big, right? They're wide and long, kind of like the shoes a clown wears. Their area is much larger than yours, so the pressure that you exert on the snow is much less than the pressure you would without show shoes.

So, to answer your question, snow shoes work by lowering the pressure that your feet apply to the snow, so that the snow can push back enough to stop your from breaking its surface.

(published on 10/22/2007)