We all know that many objects actually will float on water, but a piece of steel will quickly sink to the bottom; so, how does a giant steel riverboat float? Actually it is the same reason that wood, Styrofoam or other items float - AIR.
Any material can be made to float if you can enclose air in a watertight space. Wood and other materials that seem to float "naturally" if viewed under a microscope will be seen to have many tiny watertight pockets of air embedded throughout their fabric.
To make a piece of steel (or aluminum foil) float you first must form it into a watertight shape that encloses air. The larger the watertight space the better your steel vessel will float.
Once you have mastered this step you are well on your way to building a boat. At this point you will begin to realize that a good riverboat captain better have a good background in mathematics. Mathematics is critical in determining the safety of the vessel and how much weight it can handle. Math also is required for plotting your course, but that is another lesson.
Before leaving the dock, a good captain must determine the "displacement" of the vessel. Displacement means how much water does the vessel displace or replace. You can find out how much your vessel weighs if you determine how much water it displaces when it settles into the water - measure how much of the vessel is under water. For example, if your vessel is 30 feet wide, 80 feet long and 4 feet deep in the water, the area of displacement is 30'x 80'x 4' = 9,600 cubic feet. One cubic foot of water weighs 62.4 lbs, thus your vessel weighs 9,600 x 62.4=599,040 lbs or 299.5 tons.
Using this method you also can determine how many one cent coins can be loaded into your aluminum foil vessel under ideal conditions. Obviously, you will want to convert the figures to inches and ounces. If you have some truly enthusiastic students who want to do the calculations for extra credit you could give them the weight of water for a cubic foot (62.4 lbs.) and see if they can figure out how to get the weight of a cubic inch. If they need some help, tell them there are 998.4 ounces (62.4 lbs. x 16 oz.) in a cubic foot of water and 1,728 cubic inches (12 x 12 x 12). Thus, a cubic inch of water weighs .578 oz. (998.4 oz. /1,728 cu. in. = .578). The other figure you need is the weight of a Lincoln cent coin --.11 ounces.
If they still need assistance tell them to measure the watertight area that is created inside the vessel they have created with their piece of aluminum foil. For example, if you have a 6" x 12" piece of foil and fold it in a square shape with 1" high sides you end up with a vessel that is approximately 4" wide x 10" long x 1" deep. In a perfect world the foil vessel would stay afloat until the weight of the vessel and its load equals the weight of the water that is displaced: 4" x 10" x 1" = 40 cubic inches x .578 oz. (the weight of one cubic inch of water) =23.12 oz. If you divide this displacement weight of 23.12 oz. by the weight of a penny (.11 oz.) you discover that under absolutely perfect conditions the maximum number of pennies you could load before your vessel sinks is 210. In actual practice it would be virtually impossible to do this because you most likely would not be able to distribute the load perfectly. Real vessels are required to have a substantial margin for error.
Any material can be made to float if you can enclose air in a watertight space. Wood and other materials that seem to float "naturally" if viewed under a microscope will be seen to have many tiny watertight pockets of air embedded throughout their fabric.
To make a piece of steel (or aluminum foil) float you first must form it into a watertight shape that encloses air. The larger the watertight space the better your steel vessel will float.
Once you have mastered this step you are well on your way to building a boat. At this point you will begin to realize that a good riverboat captain better have a good background in mathematics. Mathematics is critical in determining the safety of the vessel and how much weight it can handle. Math also is required for plotting your course, but that is another lesson.
Before leaving the dock, a good captain must determine the "displacement" of the vessel. Displacement means how much water does the vessel displace or replace. You can find out how much your vessel weighs if you determine how much water it displaces when it settles into the water - measure how much of the vessel is under water. For example, if your vessel is 30 feet wide, 80 feet long and 4 feet deep in the water, the area of displacement is 30'x 80'x 4' = 9,600 cubic feet. One cubic foot of water weighs 62.4 lbs, thus your vessel weighs 9,600 x 62.4=599,040 lbs or 299.5 tons.
Using this method you also can determine how many one cent coins can be loaded into your aluminum foil vessel under ideal conditions. Obviously, you will want to convert the figures to inches and ounces. If you have some truly enthusiastic students who want to do the calculations for extra credit you could give them the weight of water for a cubic foot (62.4 lbs.) and see if they can figure out how to get the weight of a cubic inch. If they need some help, tell them there are 998.4 ounces (62.4 lbs. x 16 oz.) in a cubic foot of water and 1,728 cubic inches (12 x 12 x 12). Thus, a cubic inch of water weighs .578 oz. (998.4 oz. /1,728 cu. in. = .578). The other figure you need is the weight of a Lincoln cent coin --.11 ounces.
If they still need assistance tell them to measure the watertight area that is created inside the vessel they have created with their piece of aluminum foil. For example, if you have a 6" x 12" piece of foil and fold it in a square shape with 1" high sides you end up with a vessel that is approximately 4" wide x 10" long x 1" deep. In a perfect world the foil vessel would stay afloat until the weight of the vessel and its load equals the weight of the water that is displaced: 4" x 10" x 1" = 40 cubic inches x .578 oz. (the weight of one cubic inch of water) =23.12 oz. If you divide this displacement weight of 23.12 oz. by the weight of a penny (.11 oz.) you discover that under absolutely perfect conditions the maximum number of pennies you could load before your vessel sinks is 210. In actual practice it would be virtually impossible to do this because you most likely would not be able to distribute the load perfectly. Real vessels are required to have a substantial margin for error.
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