fluid mechanics Flashcards
fuckery
Fluid flow
the natural science of fluids in motion
Fluid forces effect
In some cases fluids have little effect on an objects motion eg shot-put and in some cases fluid forces have significant effect eg swimming and cycling
3 major fluid forces
Drag (works horizontally)
Lift (works vertically)
Buoyancy (works vertically)
Air resistance
Increased air resistance- kicking into the wind will decrease the time in the air and decrease the distance a ball can travel
Air resistance and surface area
The greater the surface area the greater the air resistance
Boundary Layer
Thin layer of surrounding or attached to the ball- determines how much drag is produced
Boundary later separation
Where boundary layer breaks away from the ball, the earlier the the separation the greater the pressure gradient between front and back of the ball leading to increased drag
Laminar flow
A type of fluid flow in which fluid moves smoothly in individual layers or streams
Turbulent flow
Flow in which the velocity at any point varies erratically
Inverse velocity and pressure relationship
When a fluid is flowing at low velocity, it will have high pressure and vice versa
3 Factors affecting boundary layer separation
Velocity
Surface Roughness
Shape
Rough surface
Causes the boundary separation to take place later, this causes a smaller pressure differential between front and back of the ball as their is only a small pocket of turbulent wake at the back of the ball
Smooth Surface
Causes the boundary separation to take place earlier, this causes a large pressure differential between the front and back of the ball as their is now a large pocket of turbulent wake at the back of the ball
Low Velocity
A low velocity causes the boundary separation to take place later, this causes a smaller pressure differential between front and back of the ball as their is only a small pocket of turbulent wake at the back
At high velocity
At high velocity causes the boundary layer separation to take place earlier, this causes a larger pressure differential between front and back of the ball as their is a large pocket of turbulent wake at the back
Oval Ball
An oval ball causes boundary separation to take place later, this causes a large pressure differential between front and back of the ball as their is only a small pocket of turbulent air at the rear of the ball
Round Ball
A round ball causes boundary layer separation to take place earlier, this causes a large pressure differential between from and back of the ball as their is a large pocket of turbulent wake at the rear
The greater the pressure gradient
the greater the drag
What is a low pressure differential
Pressure is high at the back and front of the ball and velocity is low at the front of the ball
How do objects move
Always from high to low pressure areas- an object experiencing high pressure above it will move downwards
What is form drag
resistance to forward motion as a result of a pressure differential between the front and back of an object
Magnus effect
When a ball is struck by an eccentric force the rotating ball interacts with oncoming air and the resulting curve is known as the Magnus effect
How does Magnus effect take place
Air flowing in the same direction as the boundary layer will flow at a higher velocity, therefore lower pressure. Air flowing in the opposite direction will flow at a lower velocity and higher pressure. This pressure exerts force on the ball causing a flight path deviation
3 types of spin
side, top and back
Top Spin
used in tennis. A high pressure on top of the ball and low pressure on the bottom of a ball causes it to dip
Backspin
A high pressure on the bottom of the ball and a low pressure on the top of a ball causes it to hang- golf
Sidespin
A high pressure on one side of the ball and a low pressure on the other side cause it to curve eg free kick in soccer
What does spin affect
Both the flight path of a ball and the way it bounces
Fluid resistance
As an object moves through a fluid it disturbs it. The greater the disturbance to the fluid, the greater the transfer of energy from object to fluid
2 factors affecting fluid resistance
Density (air)
Viscosity (liquid)
Density
The more dense the fluid the more disturbed the fluid becomes and hence the greater resistance
eg of density
Humid conditions create more dense conditions so a ball ill encounter greater levels of resistance
Viscosity
The more the viscous the fluid the more disturbed the fluid becomes hence greater resistance
eg of viscosity
Water is more viscous than air and a swimmer will experience greater resistance than a runner
Buoyancy
Refers to the upward force that keeps things afloat and is used to counteract the effect of gravity
Explain buoyancy
when the forces of the object are equal to or less than those of buoyancy the object will float
Centre of Buoyancy
Is the COG of water displaced by the body
COG AND COB
When the body parts and cog fall outside the cob, the body will rotate in the water in try and bring them into alignment
Positive/negative Buoyancy
Displaces a volume of fluid greater than its weight and will float
Bernoulli’s principle
Is based on pressure differences. Objects can be designed to to create low pressure above them and high pressure below them because of their shape- creating lift
How can lift act and eg
Upwards eg aeroplane wing or downwards eg racing car
Lift
Occurs because objects are forced to move from areas of high pressure towards low pressure
When does lift occur
When objects are spinning
Downward pressure racing car
A high pressure zone above the car and low pressure zone below the car ensures there is downward presto helping the car stick to the ground
Drag
Is a force pulling an object backwards due to a low-pressure air pocket created behind the object
Total Drag
Is a combination of form, wave and surface
Surface drag
It is the friction produced between fluid and the surface of a moving object
3 factors affecting surface drag
Surface area of object
Smoothness of object
Velocity of moving object
Effect of form drag
When the area of high/low pressure meet a turbulent pocket of fluid is create resulting in a function like effect slowing the body down
3 factors affecting form
Shape of object round vs oval
Velocity of object
Surface roughness
Wave drag
Is the resistance formed by creation of waves at the point where air and water interact
3 factors affecting wave drag
Velocity of the wave
Technique- streamlined
Open water vs closed conditions
4 environmental factors affecting drag
Air density
Temperature
Atmospheric pressure
Humidity
