What Makes a Snowball Hold Together?

It’s a nice idea, because snowflakes certainly do have beautifully complex shapes, with spikes, lacy edges, and all the rest. But interlocking hooks and loops are a bit too much to expect. Besides, they’re much too fragile and brittle; when you pack them together they suffer a crushing experience.

The answer lies in the fact that pressure can melt frozen water, ice or snow.

When you press the snow together tightly, the pressure melts certain portions of the flakes. They can then slide over one another on the resulting water film, and the ball compacts. But the main body of the snow is still below the freezing temperature, and the melted parts quickly refreeze. This refrozen ice acts like a cement that holds the whole thing together.

If you are intrepid enough to be making snowballs with your bare hands, your body heat is also melting a thin layer on the outside surface. When this layer refreezes, you’ve got yourself a case-hardened weapon. Although the Geneva Convention strictly forbids it, some combatants dip their snowballs in water to make them even harder.

For Yankees only: Put a dark-colored dish in the freezer and wait for snow. When it starts snowing (that’s usually when the flakes are biggest), take the dish outside with a magnifying glass, the most powerful one you can find.

A cold microscope and slide would be even better. Catch some snowflakes on the dish or slide and quickly examine them with the magnifier. What beautiful crystals! If the snow catches you unprepared, a piece of cold, dark cloth will also work as a flake catcher.

Does it ever get too cold to make snowballs?

Yes. Every northern kid knows that wet snow makes the best snowballs. That’s because snow that’s not too much colder than the freezing point is easy to pressure-melt, and it will therefore compact into an effective projectile.

But when the snow is too cold, the strength of even the most belligerent bully will be inadequate to pressure-melt and refreeze many flakes, and the snow will fall apart into useless shrapnel.