FINAL: Swim Flashcards
Water is much denser than air. What does this affect?
lift, drag, and buoyancy experienced by swimming animals
What does the generation of lift require?
constant movement of air over the wings (due to the movement of the air, the movement of the animal, or both)
What allows animals to remain suspended in water without the need to move?
buoyancy
What are the forces acting on swimming animals?
forward: thrust
backward: drag
upward: lift, buoyancy
downward: weight
What are the forces acting on flying animals?
forward: thrust
backward: drag
upward: lift
downward: weight
Do horizontal pressures on a submerged object differ?
no – they are the same, therefore they cancel each other out
Do vertical pressures on a submerged object differ?
yes – therefore there is a vertical pressure gradient (hydrostatic pressure increases with depth)
Negative Buoyancy
sink
- water volume = object volume
- density of surrounding fluid < density of submerged object
- mass of displaced water < mass of submerged object
- apparent mass of object = mass of object - mass of displaced water
Neutral Buoyancy
- water volume = object volume
- mass of displaced water = mass of submerged object
- buoyant force is directly proportional to volume and mass of displaced water
- apparent mass of object = mass of object - mass of displaced water = 0
Positive Buoyancy
float
- water volume = object volume
- mass of displaced water > mass of submerged object
- buoyant force is greater than weight
- apparent mass of object = mass of object - mass of displaced water
What does the volume of water that must be displaced to balance the weight of the object depend on?
density of water
What can affect water density? (2)
- salinity
- temperature
What is the Plimsoll line?
line painted on side of ship’s hull that marks the depth to which it can be safely loaded in different waters
line indicates height of water level on the side of the hull – equivalent to hull’s displacement (volume submerged)
Animals swimming in water may sink or float. What can they do to maintain position? (2)
- can expend energy to maintain position
- can achieve neutral (or near neutral) buoyancy
What are the methods/structures for the reduction of dense substances to lower overall density (and increase buoyancy)?
- make skeletons from cartilage instead of ossified bone
- loss of protective shells
- fatty livers that are mostly oil (lower density than water)
- fatty blubber
- modify ionic composition to include less heavy ions (but keep body fluid at same osmolarity as seawater)
- rigid gas-filled structures (ie. shell)
- flexible gas-filled structures (ie. swim bladder)
What is the centre of mass (or gravity)?
unique point in an object/system which can be used to describe the system’s response to external forces and torques
- point where the weighted relative position of the distributed mass sums to zero
- or the point where (if force is applied to it) it moves in the direction of the force without rotating
- location where all the mass of the object could be concentrated at a single point
What is the centre of buoyancy?
equal to centre of mass of water displaced by the object
located where centre of mass of object would be if it had uniform density (always in the middle)
centre of buoyancy below centre of mass
body is unstable
opposing buoyant (up) and weight (down) forces will produce a rotational force (pair of ‘turning moments’) that will roll the object to establish a stable condition
centre of buoyancy above centre of mass
body is stable
if object is deflected, the two forces will produce a rotational force to roll it back to its stable condition
centre of buoyancy at centre of mass
body is neutrally stable
centre of buoyancy and centre of mass not in the same position along the body
unstable
The centre of buoyancy and centre of mass is not in the same position along the bodies of sharks. What tends to happen to sharks?
shark pitches forward/down until buoyancy and weight are acting along same position along the body
- but horizontal position of shark is maintained by upwards-directed force generated by the fin (A)
- weight of shark is supported by sum of buoyant force and lift force (A)
What is Newton’s 3rd Law?
rate of momentum change of water, in the direction opposite to swimming direction, will result in a thrust force on the swimmer
Momentum (mass x velocity) must be conserved. To go forwards, you must push something backwards. How can the momentum of water be changed?
- lift-based propulsion
- drag-based propulsion
- jetting