This page contains the material submitted to the local paper - The Davis Enterprise - for Explorit Science Center's news column published in that paper on Fridays.

Explorit Science Center's current exhibition, Inventors and Inventions Through the Centuries, documents the creation of many useful (and often fun) items through time. For example, the giant "inventions time line" on display starts way back circa 600,000 B.C. when humans first realized how to build fires. Another example of an early invention that is still is use today is the boat.

Boats were first invented circa 7,500 B.C. in the Mediterranean. This makes boats one of the earliest of all human inventions. Although they probably didn't fully understand the physical principals that allowed boats to float, early humans certainly recognized their usefulness.

So how does a boat float? Generally, things that float are "lighter" (less dense, really) than water; things that sink are "heavier" or more dense. Explorit has a station where you can challenge this concept by using some clay and a tub of water. When you place a lump of clay in the water, its mass pushes it down. The water pushes back upward with an "upthrust" or buoyant force equal to the mass of water displaced by the object. Since a ball of clay is more dense than the amount of water it displaces, it sinks. When you mold the same clay into the shape of a boat, though, it then displaces more water--in fact its own mass in water--and so it floats.

If you would like to try this at home and don't happen to have some clay handy, you can use other objects such as ice cubes and paper. Put an ice cube in a glass of water. Does it float or sink? What does that tell you about the density of frozen water compared to that of liquid water? At risk of giving away some answers here, it is important to note that water is the only substance that is less dense in its solid form than in its liquid form. As water freezes, the water molecules become less tightly packed (or less densely packed), so the same mass of frozen water will have a larger volume than liquid water. (This is why soda bottles left in the freezer too long will crack.)

OK, so you've made a primitive boat with your ice cube. Try floating a piece of paper in a large bowl of water. What happens and why? Does anything change when you add cargo (such as pennies) to your boat? What happens when you fold your original paper raft so that it has sides like a proper boat? How does this affect the amount of cargo that it can carry? Does it matter how high the sides are in relation to the bottom of the boat?

Hopefully you now have a better understanding of what floats your boat than the original inventors did, but you might not be quite as appreciative of boats as a means of transporting people and goods. After all, the wheel wasn't invented for more than 4,000 additional years!

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Explorit Science Center is located at 3141 5th Street in East Davis. The current exhibition is Inventors and Inventions Through the Centuries. Public hours are Saturday from 11:00 a.m. to 4:30 p.m., Sunday from 1:00 to 4:30 p.m., and Tuesday through Friday from 2:00 to 4:30 p.m. Regular admission is $3; members, teachers (with school ID) and children under 4 are free.