How to build the perfect snowman (920)
By Helen Thompson | Smithsonian.com
Building the perfect snowman can be a challenge. Often snowmen can turn out a little lumpy or
lopsided. They can quickly melt into unrecognizable shapes. When you decide to build one, it
helps to have science on your side.
Understanding the physical properties of snow can help you figure out whether a snowman is
even possible. Scientists classify snow based on its moisture content, or the amount of free water
relative to ice crystals. Snow comes in five categories. It can be dry (zero percent water), moist
(less than 3 percent), wet (3 to 8 percent), very wet (8 to 15 percent) and slush (more than 15
percent).
Moist to wet snow is ideal for snowman building, according to Jordy Hendrikx, a snow scientist
at Montana State University. Dry snow is like a loose powder. Its particles don't stick together
well. Slush is too fluid to hold a shape. "You can think of the free water as the ‘glue.' You need
enough to stick the crystals together, but not too much. Otherwise it won't form a solid
snowman," says Hendrikx.
The air temperature during a snowstorm determines the amount of water in snow. Wet and moist
snows fall at around 32 degrees Fahrenheit. Temperatures that are far below-freezing make for
drier snow. More water particles freeze into crystals. "Years of experimentation and research
with my kids reveal a snow-to-water equivalence of about 5:1 yields the snow ideal for building
the perfect snowman," says Dan Snowman. He is a physicist at Rhode Island College in
Providence.
This blend of moist or wet snow falls when it is a degree or two above or below freezing. The
blizzards in the Northeast this winter would make moist or wet snow.
Dry powder is more likely during frigid conditions. Powder offers a soft, smooth ride that is ideal
for skiing. But it's not for building snowmen.
Once the snow is on the ground, it's time to build your snowman. Spheres are the best building
blocks. Forming snowballs and packing the snow together exerts pressure on the ice crystals. The
pressure makes some crystals melt during construction. "After melting, the water will crystallize
once again, binding together the snowball," Snowman notes.
To keep the spheres from toppling, stack them in the usual large to medium to small structure.
"Keeping the snowman's center of mass low is paramount in the construction of any snowman,"
says Snowman. The center of mass refers to the point in any object where its mass is
concentrated. The closer that point is to the ground, the less likely a vertical object is to fall over.
Students at Bluefield State College in West Virginia see snowman-building as a way to teach
basic engineering principles. They say the optimal diameter ratio for the snowballs is 3:2:1 from
bottom to top. This ratio keeps the base large enough to support the combined weight of the top
two snowballs. And don't build your snowman too big. The water content of the snow may limit
the size of the spheres.
Building your snowman in spheres can also help it last longer. Because the shape minimizes the
surface area exposed to rising temperatures, it slows down melting. Unfortunately, melting is
inevitable as temperatures rise. Thanks to Frozen, we all know what happens to snowmen in
summer.
Possible Response Questions:

Explain how moisture in snow acts like "glue," and explain why too much or too
little doesn't work.
 What is this main idea of this article?