Fluids and Pressure
Chapter 3
Fluids
Any material that can flow and take the
shape of its container
*Fluids include gases and liquids
All Fluids Exert Pressure
Remember Boyles Law
Calculating Pressure
Pressure = Force / Area
Area = Force / Pressure
SI unit for pressure is pascal
Written 1 Pa
Remember
– Force = Newton
– Area = m2
Math Break
Turn to Page 62
1. Find the pressure exerted by 3,000N
crate with an area of 2m2
Hint:
Pressure = Force / Area
Solution
Force = 3000 N
Area = 2 m2
Pressure = ?
Pressure = 3000N / 2 m2
= 1,500 Pa
Question 2
Find the weight of a rock with an area of
10 m2 that exerts a pressure of 250 Pa
Solution
Area = 10 m2
Force = ?
Pressure = 250 Pa
Force = 250 Pa x 10 m2
= 2,500 N
Atmospheric Pressure
The small amount of pressure (weight)
caused by the Atmosphere
Approx: 101,300 N or 101,300 Pa
http://www.wfu.edu/physics/demolabs/dem
os/avimov/fluids/marshmallow_man/marsh
mallow_man.MPG
Example
Water Pressure
Increases with depth
Is denser than air so it exerts more
pressure
Fluids Flow from High Pressure to
Low Pressure
Think about drinking straws
Pascal's Principle
Pressure applied to an enclosed fluid is
transmitted undiminished to every part of
the fluid, as well as to the walls of the
container.
http://webphysics.davidson.edu/physlet_re
sources/bu_semester1/c23_pressure_pas
cal.html
http://www.wfu.edu/physics/demolabs/dem
os/2/2b/2B2042.html
Automobile Hydraulic Lift
Quick Lab
Page. 66
Turn in question 6
Page 64 Questions 1-3
Buoyant Forces
The upper force that fluids exert on an
object
Law of Archimedes:
The buoyant force is equal to the weight of
the replaced liquid or gas.
http://www.youtube.com/watch?v=vJ36urazDu4
Weight vs Buoyant Force
Use figure 10 on page 69
Draw 3 objects not listed in picture that
would
Sink, Float and Float on the surface of
water
Draw forces using arrows
The Mystery of Floating Steel
*Remember
D= m / v
How Fish Float
The swim bladder
allows fish to change
there density
This allows them to
float at different
depths
How does increasing
volume affect the
fishes floating?
Page 71
Quick Lab: Ship-Shape
Turn in Question 3
Due Before the end of Class
Homework Page 72 (1-3)
Homework
Page 72 Question (1-4)
Bernoulli’s Principal
As speed of a moving
fluid increases, it’s
pressure decreases
Swiss Mathematician
Example Shower
Curtain
Page 73
Quick Lab
Turn in a Diagram of results and Question
3
Label High and low pressure
Page 77 (1-4)
Quick Lab
b Hold one end of a
small sheet of paper
in both hands. Keep
the held edge
horizontal while the
other end sags under
its own weight. Blow
steadily over the top
of this horizontal
edge.
Terms To Know
The upward force that pushes against gravity
The fluid force the opposes motion
of the object
The forward force produced
by fling object (planes
engine)
Wings are Not a Requirement for
Flight
Curveball exhibit Bernoulli’s
Principal
Biplane
Airship
Jet
Glider
Pick any two of the following aircrafts and
compare and contrast them in terms of lift, drag,
thrust and gravity? What are the characteristics
of each that allow them to fly?
Short Review
Fluids in Pressure
– Pressure in Atmosphere
– Pressure under water
– Altitude and Pressure
Buoyant Forces
– Sinking, Floating, Buoying up
– Archimedes Principle
– Density
Bernoulli’s Principal
– Fluid speed effect pressure How?
– Airplane Terms
Study Guide Time
Test March 10th
Lets Make A’s