11- Fluids (dynamics and motion)

Question 1

laminar flow

Answer 1

• the streamlines of the fluid (line showing velocity and direction of layers of fluid) don’t cross
• velocity is constant throughout the fluid
• there is less drag as the fluid collides less (this is why vehicles are streamlined)
• easier to achieve at low rates of flow

Question 2

turbulent flow

Answer 2

• streamlines aren’t continuous as flow is diverted
• velocity varies in different parts of the fluid
• streamlines cross
• increased drag
• common at higher rates of flow, or at the edges of the fluid as it experiences friction

Question 3

viscosity

Answer 3

• the resistance between layers of fluid (streamlines)

- observed by comparing the rates of flow through tubes or viscometers

Question 4

mass flow rate in pipes

Answer 4

• the amount of fluid passing through a pipe per second
• always constant through a pipe
• found by density of fluidcross-sectional area of pipevelocity
• smaller area = higher velocity
• slow mass flow rate = more pressure exerted on pipe walls

Question 5

stokes law and falling spheres

Answer 5

• used to find the resistive force acting on a small sphere falling through a fluid (must be laminar flow and at a constant temperature as viscosity is temperature dependent)
• F = 6picoefficient of viscosityradius of the falling spherevelocity of the falling sphere
• resultant force on sphere is W-(U+F), but F increases with velocity, so resultant force eventually ends up as 0 when (U+F) = W (sphere reaches terminal velocity)
• when sphere is at terminal velocity, stokes law can be rearranged to find the coefficient of viscosity