6.17. (9/30) Bedload; suspended load; dissolved loads; shear stresses; frictional forces

Question 1

What is the reynold’s number?

Answer 1

relates density (mass per unit volume), velocity of water flow (m/s), and size of particle/roughness/diameter (m) divided by viscosity ()
- no units

Question 2

what happens if Re>10?

Answer 2

Turbulent (shaky, movement, with air)

Question 3

what happens if 1>Re?

Answer 3

Laminar (steady, slow stream)

Question 4

what is form drag?

Answer 4

• holds particle back
• friction
• unstable vacuum

Question 5

What is surface drag?

Answer 5

how smooth a particle is

Question 6

which is more powerful? surface or form drag?

Question 7

What does a high surface drag mean? low?

Question 8

What does a low surface drag mean? low?

Question 9

What is the equation for drag force?

Answer 9

Fd = 1/2ρwAU^2Cd

Question 10

How do we make the coefficient of drag dimensionless?

Answer 10

Cd = Fd/ρwU^2D3

Question 11

What does Stoke’s Law do?

Answer 11

settling velocity of particles

Question 12

Under what circumstances does Stoke’s Law work?

Answer 12

• laminar
• d50 = silt

Answer 13

bed shear stress/ DuBoy’s equation

Question 14

what is a newton?

Answer 14

a force

Question 15

what units does shields criterion have?

Answer 15

it is dimensionless

Question 16

What is critical shear stress?

Answer 16

τc = θ(ρ