Fluid Flashcards
What are the two types of forces that are exerted on objects by a fluid environment?
- Buoyant force
- Dynamic force
What is buoyant force due to?
Due to immersion
What is Dynamic force due to?
Due to relative motion in fluid
Define buoyant force
A vertical, upward directed force acting upon an object that is submerged or partially submerged in a fluid
What does Archimedes’ principle state
A body submerged in a fluid will be buoyed up by a force that is equal in magnitude to the weight of the displaced water
What are the two points of Pascal’s Law?
- All points of a submerged body at a given depth, will experience the same pressure
- Pressure increases in large increments with relatively small changes in depth
What is the buoyant force in terms of net force?
The net force arising from the differences in fluid pressure is the buoyant force
What happens if the object does not weigh enough to balance the difference between the upward or downward forces?
It will be accelerated upward, and the object is positively buoyant
If the weight of the object is greater than the weight of the water it displaces what will occur?
It will accelerate downward, and the object is negatively buoyant
If the object has the same weight as the displaced water what would happen?
It will have no tendency to either float or sink. This object is said to be neutrally buoyant
What are the two considerations that Archimedes’ Principle is based on?
- Weight of the object
- Amount of water it displaces
Define specific gravity
The ratio of the density of a given substance to the density of water
What is a secondary way to define specific gravity
Ratio of the weight of an object to the weight of an equal volume of water
Define center of mass
The location on the body where the cardinal planes pass through and gravitational pull is found
What percentage of standing height does COG vary between in humans?
53%-59%
Why does standing height vary?
Because humans are not of uniform mass or mass distribution
Define center of buoyancy
The center of gravity of the displaced volume of water, equal in shape and volume of the submerged object that is displaced
If an object is of relatively uniform density what happens to its COG and COB?
They will have the same location
In humans where is the COB located in relation to the COG and why?
It is located superiorly to the center of gravity because the density of the human body is not consistent, and the water displaced by the body does have a consistent density
In a floating position, which way will the line of action be?
The line of action of gravitational force through the COG will be vertically downward
In a floating position, how will the line of action of buoyant force through the COG be positioned
Vertically upward
What does dynamic fluid force act on
On a system that is moving through a fluid
What are the two components that a fluid force vector can be resolved into?
- Perpendicular component: lift
- Parallel component: drag
Define drag force
The parallel component of dynamic fluid force that acts in the opposite direction of system motion with respect to the fluid
What does drag force tend to resist?
Motion of the system through the fluid
Define surface drag
The result of friction between the surface of the body and the fluid through which it is moving
What is form drag due to
Due to a relatively higher pressure on the leading edge of the object compared to its trailing edge
Define lift force
The perpendicular component of dynamic fluid force that acts in any direction that is perpendicular to the system motion with respect to the fluid
What does lift tend to change?
The direction of system motion
What is the difference in forces exerted by molecules on lower and upper surfaces?
The lift force generated
More particles under the object = _____
upward lift
More particles above the object = ______
Downward lift
What is magnus force?
Lift force caused by rotation
