Fluid Mechanics Flashcards
Properties of a solid
definite volume and shape
properties of a liquid
has a definite volume but not shape
properties of a gas
has neither definite volume nor shape
What is a fluid
a collection of molecules held together by weak cohesive forces as well as by forces exerted by the walls of the container
which types of matter are fluid
liquids and gases only
which force mainly acts on fluids
pressure
pressure formula
pressure=force/area
in which direction is the force exerted by a static fluid on an object
perpendicular to the object
pressure is a scalar or vector
scalar
denisity formula
density=mass/volume
what does density vary with
temperature
what does pressure vary with for fluids
depth
if a fluid is at rest in a container, what must be the case
the fluid is in static equilibrium
pressure at any given depth formula
P(at depth)=P(at liquids surface)+(ro)(g)(h)
what is static pressure on a fluid referred to as?
hydrostatic pressure
pascal’s law
p1=p1, therefore F1/A1=F2/A2
what is the buoyant force
the buoyant force is the upward force exerted by a fluid on any given submerged object
what must be the case if the object is in equilibrium
there must be an equally strong upward force acting on the fluid to balance the gravitational pull
Archimedes’ principle qualitatively
when an object is submerged in a fluid, it displaces a volume of fluid equal to its volume
Archimedes’ principle in equation form
Fb=roVg. where ro is the denisty of the fluid, V is the volume of fluid displaced.
If the density of the object is greater than the density of the fluid
the object sinks
If the density of the object is less than the denisty of the fluid
the object accelerates upward
Static equilibrium for a floating ca
the upward buoyant force is the balanced by the downward force of gravity.
Also, the volume of fluid displaced is equal to the volume of the object submerged in the fluid
Floating object principle in equation form
V(fluid)/V(object)=ro(object)/ro(fluid)
The fraction of the volume of the object that is below the surface of the fluid is equal to what
The ratio of the density of the object compared to that of the fluid
Why does melting ice not change the volume of the water it was floating on
Because according to archimedes, the volume of fluid displaced is equal to the mass of the object placed in it. When ice melts, it does not change mass therefore the volume displaced is equal to what it was before the ice melted, i.e. it does not change.
types of flow of fluids
laminar flow and turbulent flow
what is laminar flow
a steady kind of flow is where each particle of fluid follows a straight path called the streamline. The paths of the different particles never cross and every particle of the fluid flows at the same velocity
what is turbulent flow
an irregular flow caused by whirlpool regions. it occurs when the particle flow above critical speed
viscocity
the degree of internal friction between the two adjancent layers of a fluid
Viscosity does not equal density
water and honey have almost the same density yet honey is much much more viscous
Ideal fluid flow conditions
- the fluid is non viscous (no internal friction)
- the flow is steady (constant velocity)
- the fluid is incompressible (constant density)
- flow is irrotational (no angular momentum)
what is the direction of the velocity of a particle
tangent to the streamline
equation of continuity
V1A1=V2A2
flow rate equation
Q=vA where v is velocity and A is the cross sectional area of the opening through which the fluid flows through
Bernoulli’s equation
p1+ 1/2(rovi^2)+(roghi)=p2+1/2(rovf^2)+(rogh2)
what has to be the case for an object to be neutrally buoyant
Fb(buoyant force)=mg, density of object=density of fluid
