If using food coloring, place a few drops of food coloring into a container of water. Pour the water into the ice cube tray, completely filling each of the compartments and place the filled ice cube tray in the freezer until completely frozen.
Cover your work area with the paper towel. When the ice is fully frozen, remove nine ice cubes from the tray and place them on the towel. Put the remaining ice cubes back into the freezer. They’ll only be used in case one of the nine ice cubes you’ve selected becomes damaged or melts before you’ve finished your arch.
It's time to get to work on building the arch! Set the first two pieces of ice on the towel, a few inches apart. This will be the base of the arch. Stack the next two pieces of ice on top of the base pieces. This is a good time to ask your friend to help hold the pieces in place for you until the arch is fully formed. Continue setting pieces into the formation, one on each side, so the arch is symmetrical. Your friend can continue to hold the arch stable as you work.
When you have four ice pieces on each side, you’re ready to set the keystone, or center stone, in place. This will be the last piece of the arch and will hold the structure together. Before setting the keystone in place, visually inspect the arch you’ve assembled thus far. Does it look like the keystone can comfortably fit into the open space at the top of the arch? If the space appears to be too small, you may need to rebuild your arch with the base pieces starting a bit farther apart. If the space seems a little too big, see if you can slide the arch together once the keystone is in place. If the angle isn’t quite right and you think you can do better, start all over! It’s okay! It’s fun trying to race against the clock to build the arch before your ice melts.
What's going on?
The arch you built was constructed of blocks with a keystone in the center that held everything in place. The arch can stand upright without toppling over because of its unique shape. Downward forces from the top of the arch are spread out along the curve of the arch until the forces reach the base. At the same time, the ground pushes back with its own force. All of these forces act together to create a strong and sturdy structure.
How does it work?
Created by the ancient Romans in the first century A.D., the arch is an engineering marvel. How can this horseshoe- shaped structure withstand the strong downward forces acting on it? It’s because of both its overall shape and the shape of its individual blocks. Precisely cut, wedge-shaped blocks are used to construct an arch. Downward forces pushing from the top of the arch squeeze the blocks together, and the forces are distributed evenly along the arch’s curve. At the same time, the ground pushes up against the curve.
PHOTOGRAPHS BY MATTHEW RAKOLA ADAPTED FROM THE NAT GEO KIDS BOOK MAKE THIS! BY ELLA SCHWARTZ