FINAL: Fundamentals Flashcards
How does pressure change with water depth?
for every 10 m increase in water depth, pressure increases by around 1 atm (101.3 kPa)
How does work scale with body mass?
- force is proportional to number of muscle fibres, which is proportional to cross-sectional area of muscle (M^0.67)
- displacement is proportional to muscle length (while a muscle can only contract by 20% of its relaxed length, the longer a muscle is the longer this 20% becomes) (M^0.33)
- work scales with body mass as M^0.67 x M^0.33 = M^1
Why is surface area to volume so
important?
- SA/V is the ratio of an animal’s inside to its
outside - animal’s surface area is the interface between it and its environment
- this determines how it exchanges oxygen, carbon dioxide, heat, nutrients, wastes, etc.
- if every aspect of an animal was to increase geometrically with its body mass (∝ volume), functions requiring large S.A. would progressively become limited
How can you avoid decreasing SA/V ratio?
get bigger in only one dimension
How does dynamic viscosity change with shear strain rate if the fluid is shear thickening?
if a fluid is shear thickening, as the applied stress increases, the dynamic viscosity of the fluid increases
because the viscosity has increased, a greater increase in shear stress is required to increase the shear strain rate of the fluid
In what way is a prairie dog burrow like a Venturi meter?
A venturi meter is a device used to measure the velocity of a fluid by passing it from a tube with a large cross-sectional area into a constriction: a tube with a smaller cross-sectional area. A manometer filled with liquid is placed with one arm connected to the large tube and the other to the small tube. When the fluid flows from the large to the small tube its velocity increases and its pressure drops, causing a pressure differential across the manometer which draws fluid up towards the lower pressure in the small tube. A prairie dog burrow has two openings, one at the top of a raised mound of earth, one flush with the ground. As air flowing over the ground hits the mound, it is forced to flow up and over the top. This causes the flow to be constricted, forcing it to accelerate and drop in pressure. Thus the burrow is like the manometer, while the raised mound of earth acts like the constriction of the smaller tube in the venturi meter. But unlike the manometer, the burrow isn’t filled with liquid, so the low pressure at the opening of the raised burrow draws air through the burrow, down a pressure gradient, from the higher pressure at the other burrow entrance flush with the ground.
What does a pitot tube measure?
A pitot tube measures the dynamic pressure of a fluid, which is proportional to the velocity of the fluid. It can therefore be used to measure fluid velocity (or airspeed). It consists of a tube with an opening that faces directly into the oncoming fluid flow. The moving fluid hits the opening of the tube and stagnates (stops) converting its dynamic pressure into static pressure. The stagnation pressure at this point is therefore the sum of the static and dynamic pressures of the fluid flow. A second opening in the tube parallel to the fluid’s flow is called the static port, and is used to measure the static pressure of the fluid. A pressure gauge (manometer) placed between these two ports will measure the dynamic pressure only.
What is Reynold’s number?
ratio of inertial forces in a fluid (related to fluid density, velocity, and characteristic length) and viscous forces in a fluid (dynamic viscosity)
dimensionless number used to predict whether flow is laminar (low Re) or turbulent (high Re)
What are features of laminar flow (low Re)?
- ordered movement of fluids along streamlines
- reversible in time
- no mixing
What are features of turbulent flow (high Re)?
- disordered flow
- non-reversible in time
- mixing
- vorticity
What is dynamic viscosity?
measure of relationship between shear stress applied to a fluid, and the resulting shear strain rate
units: Pa s
What is kinematic viscosity?
ratio of dynamic viscosity of a fluid to its density
units: Stokes (St)
Swimming at low Reynolds number is a challenging prospect. Explain what type of
motion is required to move in this environment.
requires motion in which power stroke to push animal forward and recovery stroke to re-set position of structure for next power stroke are not exact opposites of each other (ie. not time reversible)
ie. beating flagellum moving like a cork-screw or cilia bending during recovery stroke can both provide non-time reversible motion
The force a contracting pennate muscle can produce is determined by…
- length of its sarcomeres
- physiological cross-sectional area
- pennation angle of muscle fibres
any animals, particularly arthropods, use power amplifiers in their limbs because…
they generate a movement faster than muscle that activates them
A shallow tray is filled with a shear thickening liquid. You float a flat card on the surface of the fluid and then proceed to push the card horizontally across the surface of the fluid at a constant velocity by applying a force with your finger. If you double the force that you are exerting on the card, what happens to the speed of the card?
increases, but does not quite double
What is dE of a lever system?
perpendicular distance from axis of rotation to line of action of the force
What happens to material where stress begins to level out with increasing strain?
material reaches its yield point – this is when the material is strained beyond its elastic region, and begins to deform (begins to strain with little increase in stress)
