13.1 Fluid Pressure
Because the theater seat
exerts a supporting force
over a larger area, it is more
comfortable than the bicycle
seat.
13.1 Fluid Pressure
Pressure
Pressure is the result of a force distributed
over an area.
• The unit of force is the newton (N).
• The unit of area is the square meter (m2).
• The SI unit of pressure is the pascal (Pa). A
pascal is one newton per square meter (N/m2)
13.1 Fluid Pressure
Pressure
If the area of a box touching the ground is 1.5
square meters, and its weight is 2700 newtons,
what pressure does the box exert on the
ground?
13.1 Fluid Pressure
Pressure
If the area of a box touching the ground is 1.5
square meters, and its weight is 2700 newtons,
what pressure does the box exert on the
ground?
13.1 Fluid Pressure
Pressure in Fluids
Water pressure increases as depth
increases. The pressure in a fluid at any
given depth is constant, and it is exerted
equally in all directions.
13.1 Fluid Pressure
Pressure in Fluids
A fluid is a substance that assumes the shape
of its container.
• Both liquids and gases are fluids.
• Water, oil, gasoline, air, and helium are examples
of fluids.
13.1 Fluid Pressure
Pressure in Fluids
A. Particles in a liquid are tightly packed
together but are able to slide past one
another.
13.1 Fluid Pressure
Pressure in Fluids
B. Particles in a gas are far apart and travel in
straight lines until they collide with another
particle or object.
13.1 Fluid Pressure
Pressure in Fluids
Water in a glass is in contact with the walls
and bottom of the glass, and it exerts pressure
on these surfaces.
For a fluid that is not moving, depth and the
type of fluid are the two factors that determine
the pressure the fluid exerts.
13.1 Fluid Pressure
Pressure in Fluids
Each vase holds a different amount of liquid.
The liquid levels are all the same because
pressure depends on depth, not amount.
13.1 Fluid Pressure
Planetary Atmospheres
The layer of gases surrounding a planet is
known as its atmosphere. All of the planets in
our solar system have some form of
atmosphere. The weight of an atmosphere
creates atmospheric pressure at the planet’s
surface.
13.1 Fluid Pressure
Exploring Boiling Points of Chlorocarbons
1. Interpreting Tables Which planet listed in the
table has the greatest atmospheric pressure?
13.1 Fluid Pressure
Exploring Boiling Points of Chlorocarbons
1. Interpreting Tables Which planet listed in the
table has the greatest atmospheric pressure?
Answer: Venus, 9120 kPa
13.1 Fluid Pressure
Exploring Boiling Points of Chlorocarbons
2. Interpreting Tables What chemical substance
exists in all but one of the atmospheres?
13.1 Fluid Pressure
Exploring Boiling Points of Chlorocarbons
2. Interpreting Tables What chemical substance
exists in all but one of the atmospheres?
Answer: Nitrogen
13.1 Fluid Pressure
Exploring Boiling Points of Chlorocarbons
3. Converting Units The bar is another unit of pressure (1
bar = 101.3 kPa). Convert each of the given pressures into
bars.
13.1 Fluid Pressure
Exploring Boiling Points of Chlorocarbons
3. Converting Units The bar is another unit of pressure (1
bar = 101.3 kPa). Convert each of the given pressures into
bars.
Answer: Mercury, 10–14 bar; Earth, 1 bar; Venus, 90.0 bar;
Mars, 0.0070 bar
13.1 Fluid Pressure
Exploring Boiling Points of Chlorocarbons
4. Using Formulas How much force is exerted on a 2.00square-meter area of Venus’s surface?
13.1 Fluid Pressure
Exploring Boiling Points of Chlorocarbons
4. Using Formulas How much force is exerted on a 2.00square-meter area of Venus’s surface?
Answer: Pressure = Force/Area;
Force = Pressure × Area;
Force = 9120 kPa × 2.00 m2 = 9.12 × 106 N/m2 × 2.00 m2 =
2.00 × 107 N
13.1 Fluid Pressure
Exploring Boiling Points of Chlorocarbons
3. Predicting On which planet would a balloon filled with a
given quantity of helium have the smallest volume?
13.1 Fluid Pressure
Exploring Boiling Points of Chlorocarbons
3. Predicting On which planet would a balloon filled with a
given quantity of helium have the smallest volume?
Answer: The helium-filled balloon would have the smallest
volume on Venus because Venus has the greatest
atmospheric pressure.
13.1 Fluid Pressure
Air Pressure and the Atmosphere
How does air pressure change with altitude?
Air pressure decreases as the altitude
increases.
13.1 Fluid Pressure
Air Pressure and the Atmosphere
Earth’s atmosphere exerts pressure of about
101 kPa at sea level. Why aren't you crushed
by air pressure?
13.1 Fluid Pressure
Air Pressure and the Atmosphere
Earth’s atmosphere exerts pressure of about
101 kPa at sea level. Why aren't you crushed
by air pressure?
The pressure inside your body balances the air
pressure outside. The balanced forces cancel,
resulting in a net force of zero.
13.1 Fluid Pressure
Air Pressure and the Atmosphere
A can containing a small
amount of water is heated
until the water boils. Then
the can is capped. As the
can cools, the pressure
inside the can becomes
less than the pressure
outside the can. The
difference in pressure
crushes the can.
13.1 Fluid Pressure
Air Pressure and the Atmosphere
A can containing a small
amount of water is heated
until the water boils. Then
the can is capped. As the
can cools, the pressure
inside the can becomes
less than the pressure
outside the can. The
difference in pressure
crushes the can.
13.1 Fluid Pressure
Air Pressure and the Atmosphere
A can containing a small
amount of water is heated
until the water boils. Then
the can is capped. As the
can cools, the pressure
inside the can becomes
less than the pressure
outside the can. The
difference in pressure
crushes the can.
13.1 Fluid Pressure
Air Pressure and the Atmosphere
A can containing a small
amount of water is heated
until the water boils. Then
the can is capped. As the
can cools, the pressure
inside the can becomes
less than the pressure
outside the can. The
difference in pressure
crushes the can.
13.1 Fluid Pressure
Assessment Questions
1. A gymnast standing on one hand (area 0.02 m2)
pushes down on the ground with a force of 600 N.
How much pressure does the gymnast exert on
the ground?
a.
b.
c.
d.
3000 Pa
30,000 Pa
12 Pa
1200 Pa
13.1 Fluid Pressure
Assessment Questions
2. The SI unit for pressure, equal to 1 N/m2, is called
the
a.
b.
c.
d.
atmosphere.
foot-pound.
pascal.
watt.
13.1 Fluid Pressure
Assessment Questions
3. The pressure exerted by a stationary fluid is
determined by
a. the area of surface containing the fluid and the type of
fluid.
b. the weight and volume of the fluid.
c. the type of fluid and its depth.
d. the shape of the container and the weight of the fluid.
13.1 Fluid Pressure
Assessment Questions
4. Which of the following statements about fluid
pressure is false?
a.
b.
c.
d.
Pressure increases as depth increases.
The pressure at a given depth is constant.
The pressure in a fluid is exerted downward.
Liquids and gases exert pressure.
13.1 Fluid Pressure
Assessment Questions
5. Why do mountain climbers on very high peaks
need cylinders of oxygen as they approach the
summit?
a.
b.
c.
d.
The tops of the mountains extend out of the atmosphere.
The pressure of air decreases as altitude increases.
Air on the mountaintops is too cold to breathe.
Air pressure at high altitudes is too great for normal breathing.
13.1 Fluid Pressure
Put your name on your notes
and hand in before you leave.
Have a wonderful day
13.1 Fluid Pressure
Assessment Questions
1. A gymnast standing on one hand (area 0.02 m2)
pushes down on the ground with a force of 600 N.
How much pressure does the gymnast exert on
the ground?
a.
b.
c.
d.
3000 Pa
30,000 Pa
12 Pa
1200 Pa
ANS: B
13.1 Fluid Pressure
Assessment Questions
2. The SI unit for pressure, equal to 1 N/m2, is called
the
a.
b.
c.
d.
atmosphere.
foot-pound.
pascal.
watt.
ANS: C
13.1 Fluid Pressure
Assessment Questions
3. The pressure exerted by a stationary fluid is
determined by
a. the area of surface containing the fluid and the type of
fluid.
b. the weight and volume of the fluid.
c. the type of fluid and its depth.
d. the shape of the container and the weight of the fluid.
ANS: C
13.1 Fluid Pressure
Assessment Questions
4. Which of the following statements about fluid
pressure is false?
a.
b.
c.
d.
Pressure increases as depth increases.
The pressure at a given depth is constant.
The pressure in a fluid is exerted downward.
Liquids and gases exert pressure.
ANS: C
13.1 Fluid Pressure
Assessment Questions
5. Why do mountain climbers on very high peaks
need cylinders of oxygen as they approach the
summit?
a.
b.
c.
d.
The tops of the mountains extend out of the atmosphere.
The pressure of air decreases as altitude increases.
Air on the mountaintops is too cold to breathe.
Air pressure at high altitudes is too great for normal breathing.
ANS: B