Every summer, millions of people travel to the beach. Sooner or later, many of these visitors begin to play in the sand on the beach. Some of the people playing in the sand get very serious with their sand play and start building sand castles. Believe it or not, the science of physics can help you build better sand castles.

Physics helps you understand why sand will or won't stick together. Physics can help geologists and engineers understand why some soils are better than others when built upon. NASA has conducted experiments in space that study types of soil - especially sand. These experiments will help geologists and engineers know more about soils.

You don't need an advanced college degree to know that the ground acts differently during an earthquake. Sometimes, soil will act like quicksand as it shakes. Experiments in space have investigated many kinds of soil properties.

Kids already know that a little water is needed to get sand to stick together. Too much water won't let the sand mold into a shape and it easily falls apart. Scientists know that water will fill in the spaces between sand particles, causing sand grains to "connect" to other sand grains. Adding too much water causes these "connections" to fall apart, which lets the sand move.

During an earthquake, geologists have seen ground actually sink when it shakes during an earthquake. If buildings are on this soil, they will also sink into the ground and they could be severely damaged.

The soil that sinks is very wet - sometimes completely soaked. All this water causes the soil to liquefy, which means it acts more like a liquid than a solid. If you were standing on this soil when an earthquake struck, you would probably feel like you were standing on quicksand.

The process just described is called liquefaction - when soil is so wet that the space between particles is filled with water. The water lets the particles slip by each other and the entire area sinks as the particles settle. The soil will get stronger if you keep it contained within a space - we call this "confining pressure."

A good example of how this "confining pressure" can change characteristics of soil is a package of coffee. Some coffee is tightly packed into cubes or rectangles. All air was removed when the coffee was packaged - we call that "vacuum-sealed." When the package is closed up, it is very hard when touched. When you open the package, air enters and the "confining pressure" is lost as the vacuum is removed. The particles will shift and separate for use in a coffeemaker.

The soil experiments in space used wet and dry columns of sand. The columns were pressed together. In space, gravity could not pull the particles downward, although the particles could still separate. A team of researchers could still measure the force that made the sand column fall apart. They could also watch a video of the particles separating to help them watch the separation.

NASA is not conducting sand research in space to help people know how to make better sand castles, even though the results could help in their construction.

Engineers can better understand where and how to build better and stronger buildings - or even where the buildings should not be built. People who store grain and powders will better understand how and why the particles act certain ways based upon how dry or moist they are. Even NASA engineers will use this information to better understand soils on the Moon or Mars.

Go ahead - build more sand castles! Remember that NASA is also "playing" with and scientifically studying sand. Maybe you can even win a "sand castle building" contest, thanks to NASA!