fluids
molecules in fluids are loosely bound or not bound at all
liquids (bound loosely so it has a definite volume) and gases are fluids bc they can flow.
why are solids not fluids
because they are bound tightly which allows them to have a definite shape and volume
How fluids transmit force
Fluids transmit forces equally in all directions when at rest.
preassure in a fluid
The pressure in a fluid increases with depth because
of the weight of the fluid above.
preassure in a fluid formula
ΔP = ρ g h
ρ = density
g = gravitational acceleration (normally 9.8)
h = depth difference (height)
preassure units
Pascal (Pa) → SI unit, = N/m²
1 atm = 103.325 Pa
1 Torr = 1 mmHg
pascals principle
In an incompressible fluid (a fluid that can’t be squished; its volume stays the same no matter how hard you press), any increase in pressure at one point is transmitted equally throughout the fluid (a push on a fluid spreads out equally in all directions)
pascals principle formula
P = F/A
Force amplification:
If pressure is transmitted equally,
F₂ = (A₂ / A₁) × F₁
F= mg (mass x gravitational energy (9.8) )
A= if they only give u the r then its (pi x r squared)
A= length x width
hydrostatic skeleton
Fluid-filled cavity acts as a support structure.
The fluid cannot be squashed, so when the muscle squeeze one part – the fluid pushes somewhere else. Muscles contract to change shape → movement.
circular muscles
worm becomes long & thin bc it acts as a belt
longitudanal muscles
worm becomes short & fat bc the lenght of the worm contracts
Bernoulli’s Equation key ideas
If fluid speed increases → pressure decreases
If fluid speed decreases → pressure increases
A fluid only has a certain amount of energy.
If it uses more energy to move fast, it has less energy left to push sideways (pressure).
Bernoulli’s Equation
P + ρgh + ½ ρv² = constant
Where:
P = pressure energy
ρgh = gravitational potential energy
v = velocity
½ ρv² = kinetic energy
viscosity
Internal friction in fluid → resistance to flow
Higher viscosity → harder for fluid to flow
Viscosity increases when fluids get colder
Poiseuille’s Law
Flow is extremely sensitive to radius – small changes in r can cause huge changes in the flow
Bigger r – huge increase in flow
If R decreases by 20% → flow halves
If R decreases by half → flow drops by 16× (because of R⁴)
laminar flow
Flow is smoothly layered:
Highest velocity in the centre
Zero velocity at the walls (due to friction)
Archimedes’ Principle
A body immersed in a fluid experiences an upward buoyant force equal to the weight of fluid displaced.
blood flow
Narrow region → blood speeds up → pressure drops
Low pressure may cause artery collapse → blocked blood flow
Blockage in coronary artery → heart muscle death → heart attack
heart function
Atria contract first →blood fills ventricles
Ventricles contract → push blood into arteries (out of the heart)
blood preassure
Pressure is pulsatile:
Systolic (peak): ~120 Torr
Diastolic (lowest blood preassure) : ~80 Torr
Average ~100 Torr
diffusion
Net movement of molecules from high concentration → low concentration due to random thermal motion.
flux (J)
Flux = amount of substance crossing a surface per unit time.
Represents the rate of diffusion.
Higher concentration gradient → higher flux.
