PowerPoint Chapter 9 Flashcards
What is fluid mechanics?
Fluid mechanicsis the branch of physics concerned with the mechanics of fluids (liquids, gases, and plasmas) and the forces on them.
The most familiar fluid to us is?
Water
Hydrostatics?
Hydrostatics – Science of water at rest
Hydrodynamics?
Hydrodynamics – Science of water in motion
Hydrodynamics has since developed into ____ ____ to incorporate the flow of ____ and other ____ ____?
Hydrodynamics has since developed into Fluid dynamics to incorporate the flow of Air and other dynamic fluids
Majority of Fluids are ____?
Majority of Fluids are Isotropic
How can fluids be described (3)?
Majority of Fluids are Isotropic
Described by defining
-mean mass/unit volume or Density (ρ)
-Temperature (T)
-Velocity (v)
Fluids yield to ____ ____ no matter how small the ____?
Fluids yield to Shear stress no matter how small the stress
Pressure to a ____ in a closed container is transmitted without loss to every portion of the ____ and to the ____ of the container?
Pressure to a fluid in a closed container is transmitted without loss to every portion of the fluid and to the walls of the container
What is buoyancy?
Vertical Supporting Force of a Fluid, upward directed
What is Pascal’s Law?
-Pressure at a point in a fluid is equal in all directions
-Ignore horizontal forces; canceled out
-Forces on bottom of object. A higher pressure at the lower portion of an object in water. Pressure difference causes a net force known as Buoyant force
What is Archimedes’ principle?
“Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.”
What is translation (fluid buoyancy)?
Translation - an upward force exerted by a fluid opposes the weight of an immersed object
The size of the buoyant force is equal to ____________________________?
The size of the buoyant force is equal to the weight of the fluids displaced by the object.
What is positive buoyant?
Positive buoyant – object weighs < water displaced. Upward acceleration
What is negative buoyant?
Negative buoyant – object weighs > water displaced, Downward acceleration
What is the equation for buoyancy?
F(buoy) = rho(f) x V(disp) x g
rho = density of immersing fluid
V = Volume of displace fluid
g = gravity
What is the weight of water?
Weight of Water is 9800N/m3
As a scuba dive goes deeper the pressure ____?
As a scuba dive goes deeper the pressure increases
What is the science behind a flotation device?
Floatation devices
-↑ Buoyancy
-Lowering density
-Hollow construction
Describe the density of the body and different tissues?
The Body
-Its density is close to water
-Approx. 70% Water
-Muscle & Bone > Density than H2O
-Body Fat < Density of H2O
What is the center of buoyancy?
-The center of gravity of the displaced volume of water, equal in shape and volume of the submerged object it displaced.
-The point where force of buoyancy seems to be concentrated
-Higher than Center of Gravity
Describe dynamic fliud forces (what do they act on)?
Acts on a system that is moving through a fluid
The system deflects fluid particles to the outside in order to move through it.
What is dynamic fluid force?
Dynamic Fluid Force – The equal and oppositely directed force of the fluid particles in reaction to the applied force of the system moving through the fluid
What are two fluid forces?
The 2 Fluid Forces
Drag – parallel
Lift – perpendicular
What is relative motion?
Relative motion
-The motion of one object with respect to a reference point
-60mph. Car next lane. Vs Car in opposite lane
What is viscosity?
Viscosity
-A measure of the resistance of two adjacent layers of fluid molecules moving relative to each other
Internal friction of a fluid
More viscous fluids move more slowly
Less viscous fluids move more quickly
What is drag?
The force resisting motion between object and fluid.
Acts parallel to the flow of fluid by an object but opposite the direction of object motion.
Drag forces tend to ____ ____ the motion of the projectile through fluid?
Drag forces tend to slow down the motion of the projectile through fluid.
What effect does fluid density have on drag?
Effect of Fluid Density
-As Fluid Density increases so does drag force
What is the formula for drag?
F^D = ½ x C^D x p(rho) x A^p x V^2
FD- Drag force
CD- Coefficient of Friction
P- fluid density
Ap- Frontal area of projectile
V2- relative Velocity
What is the coefficient of drag?
Unitless quantity that expresses the capability of an object to create drag
What does the coefficient of drag depend on?
Depends on:
-Shape of object
-Texture
-Orientation relative to fluid flow
Higher Coefficient of drag = _______________________?
Higher Coefficient of drag = greater ability to generate drag force
What are the two kinds of drag forces?
Surface Drag
Form Drag
What is a boundary layer?
Boundary layer: the layer of fluid in immediate contact with the system in motion through a fluid
What is laminar flow?
Laminar flow: fluid flow in which the molecules of fluid in the boundary layer follow the same smooth unbroken path completely around the object
What is streamline?
Streamline: the path followed by the molecules of a layer of fluid
What is fluid friction?
Fluid Friction
-Friction between fluid molecules and the surfaces of the object
What are two names for fluid friction?
Known as skin friction or viscous drag
Use a surfer to explain surface drag?
Best Example…….. The surfer
-The board creates a Boundary layer
-Layer of fluid in contact with the object as its moving through.
-Fluid closer to the board moves slower than the rest of the ocean water bc of surface drag
-The change in flow gets smaller and smaller with each successive layer until no friction is is present in outermost layers
-Waxing the surf board to ↓ friction of water and surface drag.
What is surface drag affected by?
Surface Drag affected by:
Coefficient of Drag, Density of Fluid, Projected area, relative velocity
What is form drag?
Resistance force to fluid flow created by a pressure differential when fluid flows around a submerged object.
What are other names for form drag?
Also known as Pressure Drag, Shape Drag, Eddy Drag
What is the largest fluid resistance in many sports?
Form drag
How is form drag created?
Collision of the object and molecules of fluid create:
High pressure on the front of the object
Low pressure in the wake of the object.
(Resistance does occur with increased pressure
Bullet in water concept. Loses velocity quickly)
What are the two different types of flows?
Laminar flow
Turbulent flow
Laminar flow?
Low velocity conditions, streamlined objects, mostly undisturbed parallel layers
Turbulent flow?
Fluid molecules bounce off object and each other mixing in chaos
What is a water eddy?
Noticeable disruption in streamline resulting in Turbulent water flow.
Transition between ____ and ____ is not distinct?
Transition between laminar and turbulent is not distinct
For a sphere. The ____ ____ ____ can change and dramatically effect the response of the ball during a game?
For a sphere. The coefficient of drag can change and dramatically effect the response of the ball during a game.
(Ex. Baseball/ softball pitching, Golf ball, Basketball, Volleyball, Tennis)
What are two ways to decrease drag pressure for humans?
Decrease Frontal area
Streamline
What is form drag affected by?
Affected by:
-Coefficient of Drag
-Texture of object surface
-Density of fluid
-Projected area
-Relative velocity
Drag increases when shape leads to ____ ____ ____ behind the moving object?
Drag increases when shape leads to low pressure zone behind the moving object
What is wave drag?
A disturbance will create waves within the fluids that resist the motion of an object with area projecting at this surface.
Why do objects not fall at the same rate?
Drag force
What is terminal velocity?
The velocity at which drag force is equal to the weight of the falling object, and the object will no longer accelerate
Drag force = weight of object, no net force exists
Describe the similarities and differences during freefall of 2 objects with the same shape and volume but 1 has a greater mass?
-Same drag force
-Different terminal velocities
-The more massive object needs more time to achieve deceleration
(Hail vs Rain drops)
What is lift?
Fluid force acting perpendicular (90degrees) to the flow of fluid
What does lift do in a system?
Lift tends to change the direction of the system in motion
What does lift depend on?
Shape, Velocity, Rotation of object
How does an airplane wing work?
Airplane Wing
-The key to lift is that wings cause air to be moved vertically downward.
-In other words, wings bend or deflect the paths of the streamlines.
Pulling the air downward lowers the pressure above the wing.
Lift doesn’t always go up. It can go ____.
____ lift ____ an object?
Lift doesn’t always go up. It can go down
Downward lift stabilizes an object
What are two ways (principles/laws) to explain lift?
Newton’s Laws
Bernoulli’s principle
What is Bernoulli’s principle?
The pressure in a fluid is inversely proportional to the velocity of the fluid.
The faster the fluid flow : the lower the pressure the fluid will exert
What is the equation for lift force?
FL = 1/2 x C(L) x (rho) x A (p) x v^2
FL = lift force
CL = coefficient of lift
(rho)= density of the fluid through which the object is moving
Ap= projected area of the object (area oriented perpendicular)
v2 = relative velocity of the object with respect to fluid flow
What is a foil?
(key to a foil)
(what ratio is key)
Any object that can generate lift while moving through a fluid
-Key: Angle of Attack is the optimal angle that maximizes lift and minimized drag
-Lift/drag ratio
-Too Steep? Lift no longer possible bc Drag > Lift this = Stall angle
What is the Magnus effect?
Lift forces created by the spin of a sphere
Size of Magnus force depends mostly on ____ and ____ ____?
Size of Magnus force depends mostly on spin and ball roughness
What principle is closely correlated to the Magnus effect?
Bernoulli’s principle stating that a fluid moving with a high flow velocity exerts less pressure than a fluid moving with low flow velocity
Why does the Magnus affect work?
Spin causes 2 phenomena
-Pressure gradient on one side of the spinning object to the other side.
-The boundary layer clings to the one side longer than other allowing for fluid particles to be deflected or accelerated.
Equal and opposite ____ ____ causes a gradual curve of the path?
Equal and opposite reaction force causes a gradual curve of the path.
Topspin creates a ____ ____?
Topspin creates a downward curve
(Downward lift force)
A knuckle ball causes ____ ____?
A knuckle ball causes no spin.
(Unpredictable trajectory)
What is the principle of spin?
Using Spin on a projectile to obtain an advantageous trajectory or bounce
Clearly- ____ ____ affect the motion of objects through a fluid?
Clearly- fluid forces affect the motion of objects through a fluid.
More ____ typically means a lower speed of projectile?
More spin typically means a lower speed of projectile
How does newton’s laws of conservation of angular momentum affect spin and coaching?
If you didn’t get the right spin. The mechanics are wrong. Coaching Cue.
