# Shipping Science: Building a Boat That Can Carry Cargo

A density doing from Science Buddies

Observations and results
Did the larger boat hull support a greater amount of weight? Did both hulls have a similar density right before sinking, which was roughly one gram per cubic centimeter—the density of water?

When you first put one of the boat hulls on the water, it should float because its total density is less than that of water. As you add pennies to the hull, its density increases and the hull floats lower. Eventually, when enough pennies are added, the hull's density roughly equals the water’s. This happens right before the penny that sinks the hull is added. The hull sinks because its density has finally become greater than that of water. Consequently, the hull’s density right before sinking should roughly equal the density of water, which is one gram per cubic centimeter. Even though the larger hull supports more weight, it also has a greater volume, and both hulls should roughly have a density of one gram per cubic centimeter right before sinking. (Your densities may not have been exactly this, but may have ranged between 0.7 to 1.3 grams per cubic centimeter. Sources of error that could be eliminated to give you an answer closer to the actual density of water include more accurately calculating the volume of each hull, using something smaller than pennies and including the hull's weight in your calculations.)

Cleanup
Be sure to recycle the aluminum foil when you are done testing your hulls.

More to explore
How does a boat float if it's heavy?, from the University of California, Santa Barbara, ScienceLine
Rainbows on Titan, from NASA Science News
Cartesian Diver, from PBS Kids DragonflyTV
How Much Weight Can Your Boat Float?, from Science Buddies

This activity brought to you in partnership with Science Buddies

### 5 Comments

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1. 1. lowndesw 06:32 PM 1/24/13

It is DISPLACEMENT, not "density", Archimedes.

Jees, I subscribe to SA to LEARN, not teach these REPORTERS. Maybe I should charge THEM.

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2. 2. lowndesw 06:39 PM 1/24/13

Why is the Plimsoll Line on a ship's hull higher for fresh water than for salt water, Science Buddy?? And, does it vary between the equator and the higher latitudes??

Bonus points for correct answers from liberals.

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3. 3. Pazuzu in reply to lowndesw 01:46 PM 1/25/13

Fresh water is less dense than salty, hence a greater volume is displaced by a ship of equal mass. And, yes lowndesw, it's pathetic how "Science Buddy" misused a key term and didn't even introduce the term "displacement." But why the purile snipe at those whom you consider "liberals"? You'd think they're more likely than you to not remember junior high school science?

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4. 4. Johnay in reply to lowndesw 08:09 PM 1/25/13

Actually, it is the density we're dealing with here. If the ship's overall density is greater than the water's, it sinks. If it's less, it floats. Regardless of displacement.

And in this experiment, the approximate density of water (and other liquids) is found by gradually increasing the boat's mass while maintaining its volume.

When speaking of boats, we usually speak of displacement. But in this case we are learning about the more general concept of density as being mass/volume, and using a boat to illustrate the point.

When someone points, look where they're pointing, not at their finger.

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5. 5. jtdwyer 01:42 PM 1/30/13

Subtitled: "A density doing from Science Buddies" - What?????

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