Transcript 10-10 Viscosity

10-10 Viscosity
•Internal friction of a fluid is called viscosity.
•Grease is more viscous than oil which is more
viscous than gasoline…different fluids posess an
intrinsic viscosity indicated by their coefficient of
viscosity (h) …or eta. See pg 295.
•F= hA(v/l) A=area…v=velocity…l = length or
linear location from 0 end.
•v/l is called the velocity gradient. (See p294)
•The SI unit for h is Pa. s…cgs unit is poise (P)
which is dyne*s/cm2 .
•Temperature is also stated, because it effects
viscosity.
10-11 Flow in Tubes:
Poiseuille’s Equation
• If a fluid had no viscosity, it would flow through a
tube without force.
• The flow through a tube requires force.
• J.L. Poiseuille (1799-1869) …unit poise…
Determined how flow occurred in round tubes and
pro’poised’ the equation ….
Q=pr4 (P1-P2)/(8hL) …where L=length …P=pressure …r
= radius… h=coeff. of vis. …Q=volume rate of
flow….which in SI units is m3/s.
• This equation is used when flow is laminar.
• Q is directly proportional to (P1-P2)…&directly prop
to r4 .
10-12 Surface Tension and Capillarity
• Surface tension is the behavior of the surface layer of a
fluid in a way that simulates a cohesive layer …sort of
like a layer of plastic around water.
• Surface tension =g …or gamma.
• g = F/L …where F is force applied on a line of any
fluid’s surface of length L.
• g = W/DA …work is done resulting in surface energy.
• See sample problem 10-14 p298.
• Surfactants can reduce surface tension.
• Adhesion…sticking to other objects…cohesion…sticking
to other molecules of the same type…. Why do
molecules stick together? …intermolecular forces
such as hydrogen bonding.
Capillarity
• See diagram 10-35 & 10-36 .
• Whether a liquid rises or falls, in a small tube,
depends on the surface tension.
• Water forms a meniscus and mercury does not
wet the sides and forms in inverted meniscus.
10-13 Pumps; the Heart and Blood
Pressure
• Vacuum pump
• Force pump
• Systolic pressure is the highest pressure in
your blood system and diastolic pressure is
the low, or resting, phase of blood pressure.
Homework
• Holt problems 1 and 3 page 337 (not sect.
rev.) Giancoli