Page 331 - NS-2 Textbook

326 NAUTICAL SCIENCES

gravity as low as possible in the hull, so that there is a 5. What is density, and how is it computed?
large amount of horizontal distance between the down- 6. Why does a hot-air balloon tend to rise in the air,
ward force through the center of gravity and upward while one filled with cold air does not?
force through the center of buoyancy. This will generate 7. With what equipment is a submarine fitted to allow
torque (force of rotation) that will tend to right the ship it to submerge?
whenever it ro11s. If the center of gravity rises because of 8. Upon what factors is a ship's stability dependent?
either intentional or unintentional addition of weight 9. What might happen if excessive weight is added
high in the ship, this righting torque will tend to de- high in a ship?
crease, and the ship's stability may be impaired to the 10. What will a ship sometimes do to lower its center of
point that it might capsize if it rolls too far. gravity in stormy seas?
Because of the foregoing, if a lightly loaded ship is
operating in heavy weathel~ it v'dll sometinles take on ad-
Problems
ditional water in tanks near the keel (bottom), or fill
empty fuel tanks with water, in order to lower its center 1. A steel cube with a volume of 1 cubic meter and a den-
of gravity as low as possible. In this condition it will be sity of 7,800 Kg/m3 is submerged in water (density
less likely to experience dangerous rolls in stormy seas. 1,000 Kg/m3). If each kilogram weighs 9.8 newtons,
The additional water is called ballast. III A. What is the weight of the cube in air?
B. What is the upward force on the cube when it is
completely submerged?
C. What is the apparent weight of the cube in water?
CRITICAL THINKING 2. A wooden cube of density 600 Kg/m3 is floating in
water.
1. Why is it important for anyone connected with water-
3
A. How much water in m will it have to displace in
craft to know something about the laws of buoyancy
order to float?
and stability?
B. Wlmt percentage of its volume will be above water
,vhen it floats?
C. How deep into the water will it sink?
Study Guide Questions
1. Who is credited with discovering the law of buoyant
Vocabulary
force?
2. State the principles of Archimedes' law. buoyant force density
3. What is the apparent weight of an object in watel~ Archimedes' law ballast
and how is it computed? apparent weight ballast tanks
4. How can a boat constructed from a material more freeboard center of gravity
dense than water float? waterline center of buoyancy