Unit 3: Fluids and Dynamics
Pressure Differences:

high
Fluids naturally flow from an area of
concentration to an area of concentration
The movement of fluids from an area of
low

higher pressure to an area of
lower
pressure
occurs in both natural and constructed systems
Atmospheric Pressure:
 Every layer of air exerts pressure on layers below.
 Gravity is pulling the air particles down.
 Air pressure changes with altitude
 Higher altitude = air is less dense (less
compression)
 Lower altitude = air is more dense (more
compression)


http://www.youtube.com/watch?v=jmQ8FWnM0
fA&feature=related
http://www.youtube.com/watch?v=7_yfiRf8Vc&feature=related
Liquid Pressure:
 Depth: the measurement or distance downwards
 The greater the depth the more liquid is pressing
down
 Lesser depth = less pressure
 Greater depth = more pressure

http://forces-in-fluidsp4.wikispaces.com/fluid+pressure
Fluid Pressure:
 The pressure of all fluids (gas, liquid) increases
with depth
 Pressure at sea level = 101.3 kPa = 1 atm
(atmosphere)
 Every 10m in depth = 1 atm
Buoyancy:
 The tendency for objects to rise or float in a fluid
 Occurs because of differences in density of the
object and fluid
Buoyant Force: upward force exerted by a fluid
Convection: the process of heat transfer through the
flow of a heated substance such as air or water
Watch Brainpop “Buoyancy”
http://www.brainpop.com/science/motionsforcesa
ndtime/buoyancy/preview.weml
http://www.youtube.com/watch?v=2afDLkJzEY&feature=related
Rising & Sinking:

If Buoyant Force is greater than Gravity Force
object will rise/float
then

If Gravity Force
object will sink
then

In natural systems: air warms  particles expand  less
dense  rises  cools  denser  sinks = convection
is greater than Buoyant Force
Reading Check Answers p. 318
1. Your eardrum is a very thin membrane that can move in response to a
difference in air pressure. If the difference in pressure on either side of
the eardrum becomes great, you experience a “pop” inside your ear as
the pressure equalizes.
2. Air pressure pushes the drink up the straw and into your mouth.
3. The straw makes such a tight seal that as you draw the juice up the
straw and reduce the air pressure inside the juice box, the box buckles
inward. The air pressure outside the juice box pushes the walls of the
box together.
Reading Check Answers p. 318
4. 101.3 kPa, or one atmosphere (1 atm)
5. Water is pumped into the submarine to control buoyancy. When water
enters, the submarine’s weight increases, making it more likely to
sink.
6. The object sinks.
Check Your understanding p.323
1. (a) The purpose of the pumping is to build up pressure inside the bottle.
1. (b) The pressure inside the bottle becomes greater than the pressure outside.
This results in fluid being forced from the area of high pressure in the bottle to
the area of low pressure outside the bottle.
2. Fluid sprays out farther from the bottom hole because the pressure is greater
at the bottom of the barrel than at the top.
3. As Tara blows into the balloon, the pressure builds inside the balloon. The
pressure increases to the point where the force outward from the pressure in
the balloon is greater than the force Tara’s lungs are able to produce.
Check Your understanding p.323
4. The air pressure at high altitude is low; so low, people cannot get
enough oxygen particles into their lungs to survive. For this reason
airplane cabins are kept at a much higher pressure than the lowpressure atmosphere they are flying through. If a door on the airplane
were to open, air would move out of the airplane from high to low
pressure.
5. (a) The illustration should show equally sized arrows up and down,
indicative of the forces of buoyancy and gravity.
5. (b) Yes, it is possible, as long as the buoyant force is equal to the
gravitational force.
Check Your understanding p.323
6. (a) The diagram should indicate high pressure inside the mattress, and low
outside the mattress. Particles in the mattress should be shown closer
together, as they are being forced together by Sascha’s weight.
6. (b) The diagram should indicate equal pressure inside and outside the air
mattress. Particles both inside and outside the mattress should have the same
distances between particles. This is because the pressure inside and outside
the mattress is the same.
6. (c) The diagram should indicate high pressure inside the mattress, and low
outside the mattress. Particles in the mattress should be shown closer
together, as they are being forced together by Sascha’s weight. This is what is
responsible for the movement of air out of the air mattress.
Fluid Mechanics

Fluid System: a system that makes use of a gas or liquid to perform
tasks

Pascal’s Principle: Force that is applied at one point is transmitted to
another point using an incompressible fluid
http://www.youtube.com/watch?v=iD55ynlUH8g


Static Pressure: the force exerted by an enclosed, non-moving fluid
when pressure is applied to the fluid

Dynamic /Velocity Pressure: the force exerted by a fluid in motion
Hydraulics
Hydraulics: the study of how liquids act when they are under pressure

Hydraulic Systems: a device that uses liquid under pressure to apply force in
order to move something
How it works



Applied Force to enclosed liquid  creates Pressure  moves liquid (along pipes,
tubes, hose)  causes Motion at other end
http://science.howstuffworks.com/transport/engines-equipment/hydraulic1.htm
http://www.bing.com/videos/search?q=pascal%27s+principle&view=detail&mid=9
7AC2EA621B670EA182397AC2EA621B670EA1823&first=0&adlt=strict
Hydraulic Fluid Transportation





Valve: a device for controlling the passage of fluid through a
pipe
Pumps: are used to give the force that pushes the liquid. Pumps
put the liquid under pressure
Liquid must be under pressure to move against the force of
gravity
A liquid under pressure can travel long distances
There are many types of pumps an dthey all work to create
areas of low and high pressure to move a liquid along a pipe.
Hydraulic Manipulation


An incompressible fluid
and transmits
a force from one point to another
http://science.howstuffworks.com/transport/engi
nes-equipment/hydraulic1.htm
Reading Check p. 328
1. Liquid.
2. When pressure is applied to a liquid that is continuous and enclosed in
a pipe or tube, the force is transmitted along the liquid.
3. A pump can be used to raise or move fluids. A pump creates areas of
low and high pressure to move fluid.
4. Fluids can be controlled and directed by opening and closing valves.
Pneumatics

Pneumatics: the use of gas in an enclosed system under pressure

Pneumatic Systems: a system in which an enclosed gas transmits a force
causing motion

A pneumatic system uses a compressor (since gas can be compressed)

Compressor: a device that that compresses air to build pressure

When pressure is released (air particles spread apart quickly) it exerts a
strong, steady force that can perform powerful tasks
http://www.youtube.com/watch?v=2B6TKCYxQVw

Problems with the systems
 Hydraulic /Pneumatic systems require pressure
to work
 Therefore a crack/hole will let fluid leak =
reduced pressure = reduced work
 Also a blockage will let fluid leak = reduced
pressure = reduced work
Reading Check p. 331
1. Hydraulic multiplication can be used to multiply the force exerted by a liquid.
2. Challenges include reaching remote locations with pipes, avoiding leaks,
minimizing resistance in pipes by avoiding twists and turns, and avoiding
blockages.
3. A hydraulic system uses liquid; a pneumatic system uses gas.
4. A vacuum cleaner has a motor that spins a fan at high speed. The fan creates
an area of low pressure inside the vacuum cleaner, and the higher-pressure air
from the room rushes into the vacuum.


http://www.youtube.com/watch?v=YlmRa9zDF8&feature=related
http://www.youtube.com/watch?v=UuK3ESGgbq
k&feature=relmfu
Check Your Understanding Answers p.333 #1 - 6, 8
Check Your Understanding Answers:
1. Sharp turns create resistance to flow; this reduces the efficiency of the
movement of fluid in the pipeline.
2. Buildup of material inside the pipeline can reduce fluid flow. Also, leaks must
be found and repaired to prevent loss of fluid.
3. (a) The sprayer is dynamic in the sense that the fluid spraying out is moving. It
is static in the sense that the enclosed fluid on the inside of the sprayer is
being squeezed, and is capable of applying a force even though it is not
moving.
3. (b) The higher pressure on the inside of the tank pushes the liquid out toward
the area of lower pressure outside the sprayer.
Check Your Understanding Answers:
4. This is accomplished with a pump; pumps can move fluids up against gravity.
5. The diagram should show two pistons of different size connected to each other by a
contained liquid. Applying force to the smaller piston will result in the force being
multiplied at the larger piston.
6. The vacuum creates an area of low pressure inside it with a rapidly moving fan. The
higher-pressure air in the room moves toward the area of low pressure, through the
vacuum cleaner hose. The cardboard is held on to the hose due to the high pressure of
the room forcing it against the hose. If you want to remove it, you must apply enough
force to overcome the force caused by the air pressure in the room.
8. The spray will be equal from both holes because pressure is distributed equally
throughout a contained fluid.


Many natural systems are based on fluids and pressures
They can be found in the atmosphere (hurricanes), inside
the earth (volcanoes), in the oceans (whirlpools), and
inside the human body.
Fluid Systems in Humans
 Humans rely on fluids and fluid systems
 Water, and water balance, is vital for life
 Humans are affected by air pressures (breathing and
fluid pressures (the circulatory and respiratory systems)
The Circulatory System (Hydraulic System)

The circulatory system transports blood through the body
Heart is the pump
Blood Vessels are the pipes
Blood is the fluid under pressure

Heart beats increase & decrease pressure

Blood leaves heart under
pressure
Blood pressure refers to how hard blood pushes against the
walls of your body's blood vessels




High
Disorders of Blood Circulation

Like in all hydraulic systems, deposits (clogs) or cracks inside of
pipes decreases the hydraulic system's effectiveness.

Fatty deposits build up in arteries to slow blood flow
Smoking and obesity also increase blood pressure



High BP = too much force on pipes (burst)
Low BP = not enough blood flow (blocked)
Reading Check Answers, p. 337
1. Like pipelines, blood vessels transport fluid from place to place under pressure.
2. If you fill a balloon with water and then push on it, the pressure moves through the
water in all directions. When the heart contracts, it places pressure on the blood in
much the same manner.
3. The first number is a measure of the pressure caused when blood is pushed out of the
heart. The second number is a measure of the pressure that occurs as the heart relaxes
and refills with blood.
4. Clogged arteries, smoking
5. Weak heart, low water levels in blood
The Respiratory System (Pneumatic system)


Inhaling expands the rib cage, increasing volume (by making a bigger space)
and decreasing pressure (in the lung)
Air from outside, which has oxygen in it, is at a higher pressure so it enters
the low pressure in the lungs

Exhaling is the diaphragm and rib muscles pushing inwards, decreasing
volume (by making smaller space) and increasing pressure (in the lung)

Air is pushed out of lungs/body
Disorders of Breathing

Breathing is affected by narrowed passageways, especially swelling from
infections and allergies

Smoke, polluted air, coal dust and asbestos are also harmful

Asthma is a respiratory disease that narrows the passageways for air entering
and leaving the lungs. Asthma can be triggered by smoke and pollutants,
exercise, stress and dust

An inhaler is used to deliver tiny droplets of medicine to passage ways
Reading Check Answers, p. 339
1. When you inhale: expansion of the chest cavity creates an area of low pressure in the
lungs.
2. When you exhale: contraction of the chest cavity creates an area of high pressure in the
lungs.
3. The diaphragm moves up and down to help contract and expand the chest cavity.
4. Bacterial or viral infections, asthma
5. Asthma attacks cause the pathway to the lungs to narrow, making it difficult to breathe.
Check Your Understanding: p.343 #1 – 3, 5 - 7
Check Your Understanding Answers
1. A hydraulic system moves fluid under pressure. This is what the
human circulatory system does.
2. Pneumatics is the use of gas (usually air) in an enclosed system
under pressure. This is what the human respiratory system does.
3. The diaphragm moves down when you inhale, enlarging the
chest cavity and creating an area of low pressure in the lungs.
This causes the higher pressure air from the surroundings to
rush into the lungs.
Check Your Understanding Answers
5. The CPR compression of the chest is a way to mimic the action of the
heart. When the chest is compressed, the heart is compressed, forcing
blood out of it to the rest of the body. This is not as good as the natural
action of the heart, but may help to keep a person alive until medical
personnel can restart the heart.
6. The heart pumps blood under pressure to all areas of the body. When
you stand up too quickly, the blood pressure momentarily drops in the
head area, interrupting the supply of blood to the brain. It takes a few
moments for the body to adjust and normalize blood pressure. In the
meantime, you will feel a bit dizzy.
Check Your Understanding Answers
7. (a) The diaphragm jerking upward causes the chest
cavity to get smaller very fast, which compresses the
air in the lungs, raising the air pressure.
7. (b) When a hiccup occurs, the rapid compression of
the chest cavity causes air to be rapidly forced out of
the lungs (this causes the hiccup sound).
Chapter Review: p. 344 #1 – 4, 7 - 10, 13
CHAPTER REVIEW ANSWERS
1. The diagrams should indicate that the air in the container
can be compressed, while the water cannot.
2. When a balloon is filled, air is forced into it under
pressure. The walls of the balloon contain the area of
high pressure in the balloon. When the wall of the
balloon is popped, the high-pressure air inside the
balloon moves rapidly outward.
CHAPTER REVIEW ANSWERS
3. The diagram should show that pressure increases with depth.
4. (a) Hydraulics uses liquid, while pneumatics uses gases (usually
air) under pressure. Pneumatics requires the use of a
compressor. Hydraulics usually uses pipes, pumps, and valves.
4. (b) Both terms describe systems that operate while under
pressure to move fluids from one place to another.
CHAPTER REVIEW ANSWERS
7. Water must often be moved great distances to areas
that are at higher elevations. Moving the water
against the force of gravity requires a pump.
8. All of the following reduce fluid flow: twists and
turns in the pipe, build-up of material inside the pipe
such as sludge or rust, pipes that are too narrow, and
leaks.
CHAPTER REVIEW ANSWERS
9. Initially the heating of the tank caused the particles inside the
tank to move farther apart, which caused some of the particles
to leave the tank. When the tank was sealed and cooled, the
remaining particles moved closer together, causing an area of
low pressure. The high pressure of the surroundings pushed
against the tank toward the low-pressure area, crushing the
tank.
10. Air flows from areas of high pressure to areas of low pressure,
causing winds.
CHAPTER REVIEW ANSWERS
13. (a) When the pump handle is forced downward,
it pushes the air particles trapped in the pump
together, compressing the air.
13. (b) The inflation needle is a very tiny tube, which
offers much more resistance to the flow of air.
Summary: Fluids Under Pressure

.
Summary: Fluids Under Pressure


Particles will move from an area of high pressure
to an area of low pressure.
Pressure in a liquid will increase with depth.
Summary: Buoyancy


Buoyancy is the tendency of objects in fluids to rise
or sink due to density differences with the
surroundings.
Buoyant force is the upward force exerted by a fluid;
if it is less than the force of gravity, the object will
sink. If buoyant force is greater than gravity, the
object will rise.
Summary: Hydraulics








Fluids in motion have dynamic pressure that can exert force to complete
tasks.
Hydraulics is the study of pressure in liquids.
Hydraulic systems create pressure that moves through a contained liquid.
Pumps force liquid to create pressure in a hydraulic system.
Valves control flow in hydraulic systems.
Hydraulic multiplication takes advantage of an incompressible fluid to
transmit and increase force from one point to another.
Pneumatics is the use of compressed air in an enclosed system.
Blockages will interfere with the flow of fluid in a hydraulic or pneumatic
system.
Summary: Fluids in Natural Systems



Humans rely on fluid systems for proper body
function. Proper water levels in the body must be
maintained.
Blood pressure is the force of blood on the walls of
blood vessels.
The human respiratory system uses changes in air
pressure for breathing. Air pressure changes are
caused by changes in chest volume.
Summary: Disorders of Natural Fluid Systems




High or low blood pressure can result in health problems.
Clogged blood vessels can reduce blood flow, increase
blood pressure, and have a negative effect on human
health.
Clogged or swollen air passageways can interfere with
breathing.
Asthma is a disease of the respiratory system that
interferes with the normal flow of air into the lungs.