Fluid Dynamics: Thrust
Lesson 7
What is Fluid Dynamics?
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Fluid dynamics helps engineers and scientists make sense of :
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how fluid moves
how fluids affect moving objects
Velocity is how fast something moves
Many things behave like a fluid
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Air
Gas
Liquid
Electricity
Traffic
Fluids are hard to contain since they take many shapes based on their
environment
Forces: What Makes the Sea Perch Move???
 Forces
are everywhere:
© alandberning
Force of Gravity
Person Applied Force to Ball
Magnetic Force
Forces and Sea Perch Movement
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Two main forces
affect the
movement of the
Sea Perch.
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Thrust: force
that allows Sea
Perch to move
forward
Drag: force that
prevents Sea
Perch from
moving faster
once in motion
*Large Picture of Sea Perch
moving through hula hoop
toward object*
Thrust
Drag
Thrust vs. Drag
© krakow.bicycles
Thrust = Drag = 0
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© Mariano Kamp
© dewonn43
Pedaling is a way of
applying thrust
The breeze in your
hair is drag
The rate at which you increase your speed on the
bike is acceleration.
However, the faster you go the stronger the breeze
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This makes the bike harder to pedal
Eventually you can’t go any faster no matter how
hard you pedal

Now you have reached terminal velocity
Thrust vs. Drag: Mathematically
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When a force is applied to a mass you
accelerate:
ma  FThrust  FDrag
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m is mass: the amount of matter in an object
a is acceleration: the rate at which you increase your vel
F thrust: the force of thrust
F drag: the force of drag
What happens when you reach terminal velocity?

F thrust = F drag and a = 0
How is a Bike Similar to the Sea Perch?
Vehicle
Thrust
Drag
Caused by peddling
Caused by air
Caused by propellers
Caused by water
© RoRRo
Propellers Cause Thrust
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What happens when a propeller rotates:
1. It pushes fluid away from the vehicle
2. It pulls fluid towards the vehicle
How Does Fluid Density Affect Propellers?
*Picture of Fan*
Propeller pushes water
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Fan pushes air
Water has about 1000 times the density of air
A gallon of water is 1000 times heavier than a gallon of air
Pushing fluid with greater density requires more thrust
Thrust force in water is then 1000 times greater than the
thrust force in air