Fluid Dynamics: ThrustFluid Dynamics: ThrustLesson 7Lesson 7

What is Fluid Dynamics? What is Fluid Dynamics?

Fluid dynamics helps engineers and scientists make sense of : Fluid dynamics helps engineers and scientists make sense of : how fluid how fluid movesmoves how fluids affect moving objectshow fluids affect moving objects

Velocity is how fast something moves Velocity is how fast something moves

Many things behave like a fluidMany things behave like a fluid Air Air GasGas LiquidLiquid ElectricityElectricity TrafficTraffic

Fluids are hard to contain since they take many shapes based on their Fluids are hard to contain since they take many shapes based on their environmentenvironment

Forces: Forces: What Makes the Sea What Makes the Sea Perch Move???Perch Move???

Forces are everywhere:Forces are everywhere:

Force of GravityForce of Gravity Person Applied Force Person Applied Force to Ballto Ball

Magnetic ForceMagnetic Force© alandberning

Forces and Sea Perch MovementForces and Sea Perch Movement*Large Picture of Sea *Large Picture of Sea Perch moving through Perch moving through

hula hoop toward hula hoop toward object*object*

Two main forces Two main forces affect the affect the movement of the movement of the Sea Perch.Sea Perch. Thrust: force Thrust: force

that allows Sea that allows Sea Perch to move Perch to move forwardforward

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

ThrustThrust

DragDrag

Thrust vs. DragThrust vs. Drag

Thrust = Drag = 0Thrust = Drag = 0 Pedaling is a way of Pedaling is a way of applying thrustapplying thrust

The breeze in your The breeze in your hair is draghair is drag

The rate at which you increase your speed on the The rate at which you increase your speed on the bike is acceleration.bike is acceleration.

However, the faster you go the stronger the However, the faster you go the stronger the breezebreeze

This makes the bike harder to pedal This makes the bike harder to pedal Eventually you can’t go any faster no matter how Eventually you can’t go any faster no matter how

hard you pedalhard you pedal Now you have reached terminal velocityNow you have reached terminal velocity

© krakow.bicycles

© dewonn43© Mariano Kamp

Thrust vs. Drag: MathematicallyThrust vs. Drag: Mathematically

DragThrust FFma

When a force is applied to a mass you When a force is applied to a mass you accelerate:accelerate:

m is mass: the amount of matter in an objectm is mass: the amount of matter in an object a is acceleration: the rate at which you increase your vela is acceleration: the rate at which you increase your vel F thrust: the force of thrustF thrust: the force of thrust F drag: the force of dragF drag: the force of drag

What happens when you reach terminal velocity?What happens when you reach terminal velocity? F thrust = F drag and a = 0F thrust = F drag and a = 0

VehicleVehicle ThrustThrust DragDrag

Caused by peddlingCaused by peddling Caused by airCaused by air

Caused by propellersCaused by propellers Caused by waterCaused by water

How is a Bike Similar to the Sea How is a Bike Similar to the Sea Perch?Perch?

© RoRRo

Propellers Cause ThrustPropellers Cause Thrust

What happens when a propeller rotates:What happens when a propeller rotates:

1. It pushes fluid away from the vehicle1. It pushes fluid away from the vehicle

2. It pulls fluid towards the vehicle2. It pulls fluid towards the vehicle

How Does Fluid Density Affect How Does Fluid Density Affect Propellers?Propellers?

*Picture of Fan**Picture of Fan*

Water has about 1000 times the density of airWater has about 1000 times the density of air A gallon of water is 1000 times heavier than a gallon of airA gallon of water is 1000 times heavier than a gallon of air Pushing fluid with greater density requires more thrustPushing fluid with greater density requires more thrust Thrust force in water is then 1000 times greater than the Thrust force in water is then 1000 times greater than the

thrust force in airthrust force in air

Propeller pushes waterPropeller pushes water Fan pushes airFan pushes air