Fluid Dynamics: Thrust

donutsclubMechanics

Oct 24, 2013 (3 years and 7 months ago)

74 views

Fluid Dynamics: Thrust

Lesson 7

What is Fluid Dynamics?


Fluid dynamics helps engineers and scientists make sense of :


how fluid
moves


how fluids affect moving objects


Velocity is how fast something moves


Many things behave like a fluid


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:

Force of Gravity

Person Applied Force to Ball

Magnetic Force

© alandberning

Forces and Sea Perch Movement

*Large Picture of Sea Perch
moving through hula hoop
toward object*


Two main forces
affect the
movement of the
Sea Perch.


Thrust: force
that allows Sea
Perch to move
forward


Drag: force that
prevents Sea
Perch from
moving faster
once in motion

Thrust

Drag

Thrust vs. Drag

Thrust = Drag = 0

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


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

© krakow.bicycles

© dewonn43

© Mariano Kamp

Thrust vs. Drag: Mathematically



When a force is applied to a mass you
accelerate:




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


Vehicle

Thrust

Drag

Caused by peddling

Caused by air

Caused by propellers

Caused by water

How is a Bike Similar to the Sea Perch?

© RoRRo

Propellers Cause Thrust



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*



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

Propeller pushes water

Fan pushes air