Glencoe Physics
Chapter 13
States of Matter
Objectives:13.1
• Describe how fluids create pressure and
relate how Pascal’s Principle to some
everyday occurences.
• Apply Archimedes’ and Bernoulli’s
Principles
• Explain how forces within liquids cause
surface tension and capillary action, and
relate the kinetic model to evaporation and
condensation
Objectives:13.2
• Compare solids, liquids, gases, and
plasmas at a microscopic level, and relate
their properties to their structures.
• Explain why solids contract and expand
when the temperature changes
• Calculate the expansion of solids and
discuss the problems caused by
expansion
Fluids
• A fluid is anything that flows (easily moves,
changes shape).
– Liquids (system is a hydraulic system)
– Gases (system is a pneumatic system)
• To move fluids, a pressure difference is
needed
Pressure
• Motion of fluids can be
understood by
understanding the concept
of pressure.
• Pressure is created by
fluids when particles of
fluid (atoms or molecules)
impact a surface.
• Pressure is defined as the
ratio of a force and the
area over which that force
is applied
F
P
A
Where P = Pressure
F = force applied
A = area over which force
is applied
**Pressure is directly
related to the number and
strength of the collisions of
the particles with container.
Evangelista
Torricelli
Pressure
1000 Pa = 1 kPa = 1000 N/m2
• Units of pressure….
– pounds/inch2 (PSI)
– newtons/meter2
(Pascal) (SI unit)
– kilopascals
– mmHg
– InHg
– Torr
– atmospheres
– bar
– millibar
• Standard Sea Level
barometric Pressure
• 14.69 psi
• 101,325 Pa
• 101.325 kPa
• 760 mmHg
• 29.92 inHg
• 760 torr
• 1 atm
• 1.013 barr
• 1013 mb
First man
To create a
sustained
vacuum,
and
discovered
principle of
the
barometer
Measurement of pressure
• Barometers
– Aneroid
Why is “Fair Weather” or “Dry Weather”
associated with higher atmospheric
pressure?
Measurement of Pressure
• Barometers
– Mercury
Measurement of Pressure
•
•
•
•
Pressure gauge
Tire gauge
Altimeter
Digital instrument
Magdeburg Hemispheres
• The Magdeburg hemispheres
were a pair of large copper
hemispheres precisely cast so
that their rims fit tightly together.
• The Magdeburg hemispheres
were designed by German
scientist Otto von Guericke in
1650 to disprove Aristotle's
famous supposition that 'Nature
abhors a vacuum'. To get the air
out of the sphere, von Guericke
also designed the world's first
vacuum pump, which consisted
of a piston and cylinder with
one-way flap valves.
Problem…..
The atmospheric pressure at sea level
is 101,325 Pa. What is the force, at
sea level, that air exerts on the top of
a typical desk, 152 cm long X 76 cm
wide? Report in SI unit.
P=F/A
PA = F
F = PA
F = 101, 325 n/m2 X (1.52 m X .76m)
F = 1.2 X 105 N
Problem…
A car has a mass of 900.
kg. If each tire on the car
has a contact area of 80.
cm2, what internal air
pressure (in Pa) will each
Area of Contact
tire have? In atm? In PSI?
P = F/A
P = (mg/4)/A
P= ((900.kg X 9.8m/s)/4) / .0080 m2
P = 275625 Pa
41 psi
P = 2.8 X 105 Pa 2.8 ATM
Fluid Pressure
• Fluid pressure can be “created” in at least
two ways
– For an enclosed fluid, the container may provide
the force (physical confinement) or there may
be an external force applied
– For an open fluid, the “weight” of the fluid
creates the pressure
Pascal’s Principle
• Blaise Pascal (1623-1662), a French
physician, noted that the shape of the
container did not affect the pressure of the
fluid that it contained, at any particular
depth.
Pascal’s Vases
Pressure in Closed System
Pascal’s Principle
• “Any change to the pressure
of a confined fluid is
transmitted undiminished
throughout the fluid”
F1 F2
P 

A1 A2
Fluid is at same pressure, everywhere……
F1/A1 = F2/A2
F1A2/A1 = F2
Basic hydraulic cylinder
Problem…
• Dentist’s chairs are examples of hydraulic
lift systems. If a chair weighs 1600 N and
rests on a piston with a cross-sectional
area of 1440 cm2, what force must be
applied to the smaller piston with a crosssectional area of 72 cm2 to lift the chair?