Buoyancy and Flotation

Buoyancy

measure of the upward force of a fluid exerts on an object that is submerged

Water exerts what type of force

upward force

Strength of buoyant force on an object depends on what

volume of the object

As you push downward, an object's buoyant force gets

stronger

Upward forces against the bottom of the object are _______ than _______ forces

greater, downward

Flotation

Gravity and Buoyancy

When the weight of the submerged object is greater than the buoyant force, the object will

sink

When the weight of the submerged object is equal to the buoyant force, the object will

float

When the weight of the submerged object is less than the buoyant force, the object will

rise to the surface

Archimedes' Principle

the buoyant force on an object is equal to the weight of the fluid displaced by the object

A 500 gram mass weights about 5 N in air. Suppose the mass displaces 3 N of water when it is submerged. The buoyant force on the mass will also measure 3 N (pointing up). How much will the mass weigh in the water?

2N

Weighted-base Stability

Used for narrow hull ships. Weight in the bottom of the hull is used as "balast" to stabilize the hull.

Leveraged Staability

A wide hull is used for stability

Center of Gravity

The sum of the entire weight of a ship acting straight downward on the geometric center.

Center of buoyancy

The center of the volume of water which the hull displaces

Neutral Stability

Ship will right itself as buoyancy shifts and pushes directly against the gravitational weight

Stiff ship

rights itself very quickly

Tender ship

tends to be a little top heavy, which means that when it rolls one way it goes far that way, then rolls far the other way. It rocks back and forth.

Negative Stability

Ship is in danger of capsizing because the weight on the right is increasing, while the buoyancy on the left is increasing ass well, creating a tendency for the heavy side to push downward and the more buoyant side to push upward

Plimsoll Lines

show the maximum depth to which a ship an safely loaded in different zones and seasons

Draft Marks

show the depth to which the hull is riding in the water