Transcript VII. Forces in Fluids

Ch. 3 & 4
Motion & Forces
VII. Forces in Fluids (Ch. 8.5)
Archimedes’ Principle
 Pascal’s Principle
 Bernoulli’s Principle

A. Archimedes’ Principle

Fluid
 matter that flows
 liquids and gases

Buoyancy
 the ability of a fluid to exert an
upward force on an object
immersed in it
A. Archimedes’ Principle

Bouyant Force
 upward force exerted by a fluid on an
immersed object
 bouyant force > weight
balloon rises
 bouyant force < weight
balloon sinks
 bouyant force = weight
balloon floats
A. Archimedes’ Principle

Archimedes’ Principle
 the bouyant force on an object in a
fluid is equal to the weight of fluid
displaced by the object
Not
More
water
needs
water
is
to displaced
betodisplaced
in order
in order
cancel
to to
Veryenough
little
water
needs
be displaced
intoorder
cancel weight
weight
 ball sinks.
 ball floats lower
in the water.
on surface.
View Buoyancy JAVA Applet.
View animations produced by students at Poly Prep Country Day School in Brooklyn, New York.
B. Pascal’s Principle

Pascal’s Principle
 pressure applied to a fluid is
transmitted unchanged throughout
the fluid
View hydraulics explanation.
F1
P 
A1
F2
A2
B. Pascal’s Principle

A car weighing 1000 N sits on a 250 m2 platform.
What force is needed on the 10 m2 plunger to
keep the car from sinking?
GIVEN:
WORK:
Platform:
F = 1000 N
A = 250 m2
Plunger:
F=?
A = 10 m2
1000 N =
250 m2
F2
F1 F2

A1 A2
10 m2
(1000N)(10m2)=(250 m2)F2
F2 = 40 N
C. Bernoulli’s Principle

Bernoulli’s Principle
 as the velocity of a fluid increases,
the pressure exerted by the fluid
decreases
 EX:airplane lift, curve balls
C. Bernoulli’s Principle
Airplane lift
View airplane wings explanation.
Curve Ball
C. Bernoulli’s Principle
Funnel Demos
View funnel explanation.
View inverted funnel explanation.
C. Bernoulli’s Principle

Venturi Effect
 fluids flow faster through narrow
spaces causing reduced pressure
 EX: garden sprayer, atomizer,
carburetor
C. Bernoulli’s Principle
Venturi Effect - Atomizers
View atomizer explanation.