Download Fluids and Viscosity Chapter 7 Particle Theory of Matter (PTM)

Chapter 7
Particle Theory of Matter (PTM)
Matter: has mass and takes up space
The Particle Theory of Matter helps explain how particles exist and act in solids,
liquids and gases.
The PTM states that:
1. All matter is made up of very tiny particles
2. There is space between particles
3. The particles are always moving. The more energy they have, the faster they
move.
4. There are attractive forces between particles.
5. All particles in a pure substance are the same but are different from other
substances.
The 3 states of matter are solid, liquid and gas. They can be described in terms of
their shape, volume, particle arrangement and particle movement. Please see and
study the table on the next page.
State of
Matter
Solid
Shape
Volume
Definite –
cannot change
shape to fit
containers
Definite – we
cannot change
the volume of a
solid without
cutting it, which
is physically
changing it. A
solid will not
grow or shrink
on its own!
Particle
Arrangement
Close – particles are
very close together
Particle
Movement
Vibrate – hit
into and rub up
against one
another but
cannot float
away or slide
past each other.
Particles are
very attracted to
each other
Liquid
Indefinite –
liquids will
change their
shape to fill up
any container
they are put in
Definite – you
Close, but not as
cannot change
close as a solid. Not
the volume of a packed so tightly
liquid. If you
glass of water
you have a glass
of water! The
water does not
grow or shrink!
Free Flowing –
they are able to
move around
more freely and
can slide past
each other. They
have enough
energy to pull
away from one
particle but are
then attracted to
another particle.
They are always
changing
partners!
Gas
Indefinite – a
gas has an
indefinite shape
because it will
change its shape
to fill any
container in
which it is
contained
Indefinite – a
gas has an
indefinite shape
because it will
expand (get
bigger) and
contract (get
smaller) to fill
the shape of a
container
Random – the
particles float
around
randomly. Free
to move in any
and every
direction. Gas
particles have so
much energy
that they
continually
collide and
bounce off each
other and stay
suspended in
mid-air.
Far apart – there is a
lot of space between
the particles
- A Fluid is any form of matter that FLOWS.
- Since liquids and gases do NOT have definite shapes, they are able to flow –
making them both FLUIDS
- We use fluids in our lives every day…
- Food Fluids: water, oil, syrup, honey
- Cleaning Fluids: shampoo, detergents, gels, VIM, Mr. Clean
- Bodily Fluids: blood, mucus, saliva
- Industrial Fluids: lube, oil, gas, compressed air in tires
- Viscosity is a measure of a liquids resistance to flow.
- We say that fluids are thick (syrup) or thin (water)
- A fluid that is VISCOUS is one that is NOT runny and flows very slowly, like
molasses!
- Friction is a force that resists movement.
- The greater the FRICTION (or rubbing of particles) the greater the VISCOSITY.
- When an object his highly viscous we know that the particles are holding on tight
to one another! They are very attractive to one another.
We need to use fluids for specific purposes. We depend on fluids having particular
viscosities in order to be able to use them! For example:
- Paint – we need paint to not be too runny (too viscous) or it would not spread on
or stay on our walls!
- Foods such as ketchup and mustard must be kept in the fridge so that the cool
temperatures keep them more viscous. If they were too runny we would have
difficulty getting them to stay on our food. Also, if peanut butter were kept in the
fridge, the cold temperature would keep it too hard to spread. That is why we keep
peanut butter on the shelf when the warmer temperature makes it easier to use!
- Motor oils are needed to keep cars lubricated. We need to use high viscosity
(thick) motor oil in summers because the warm temperatures will make them runny
(less viscous) enough to properly lubricate your vehicle. In the winter we would
need lower viscosity oil because the colder temperatures will make it more viscous
and we wouldn’t want it to be too thick that it does not do its job.
- Flow rate is the speed at which a fluid flows from one point to another. Fluids
can move slowly, quickly or at a medium speed.
Slow Flow Rate
Corn Syrup
Molasses
Medium Flow Rate
Dishwashing liquid
Some shampoos
Viscosity
High
Low
Flow Rate
Slow
Fast
Fast Flow Rate
Water
Sodas
Description
Thick and more viscous
Runny and less viscous
1. Temperature
Liquids: Increase Temperature = Decrease Viscosity (becomes more runny)
Decrease Temperature = Increase Viscosity (gets thicker)
* According to the Particle Theory of Matter, when you add heat to a liquid
the particles depend on the increase in energy to move them further apart so
that they flow past each other easier (less viscous)
Gases: Increase Temperature = Increase Viscosity (expands, get bigger)
Decrease Temperature = Decrease Viscosity (contracts, gets smaller)
* According to the PTM, temperature affects gases and liquids differently
because gas particles do not need an increase in energy (from temperature)
to move farther apart because they are already far apart!
2. Concentration – the amount of a substance dissolved in a specific volume
Increase Concentration = Increased Viscosity
Decrease Concentration = Decreased Viscosity
- Pancake batter- we can alter how viscous pancake batter is by changing the
concentration (amount) of batter or water in the mixture!
- According to the PTM, when we add more batter, we are adding more
particles to the same volume of water. More particles mean more attractive
forces and less room to move about, causing a higher viscosity.
3. Attractive Forces
Strong Attraction = More Viscous
Weak Attraction = Less Viscous
- The PTM states that the stronger the attractive forces between particles, the
less likely they are to pull away from each other or slide past each other
resulting in a more viscous fluid.
4. Particle Size
Small Particle Size = Less Viscosity (more runny)
Large Particle Size = More Viscosity (thicker)
- According to the PTM, small particles can move past each other more
easily then large particles can because they take up less space and have more
room to move.
- So, if we compare water and oil we know that the oil particles must be
larger than the water particles because oil is more viscous and has a slower
flow rate
Chapter 8
- Density is the measure of the mass contained in a given volume.
- Density also describes how tightly packed together particles are in a material.
More dense materials have more particles packed closer together.
- Mass – the amount of matter in a substance
- Volume – the amount of space occupied by a substance
- Substances with lower densities will float on substances that have higher
densities (just like we learned when we layered salty colored waters and the nonsalty waters in unit 1)
Particles
Solids
Liquids
Particles very close Particles close but
together
can slide past
Density
High density
Medium density
Gases
Particles very far
apart from each
other
Low density
- If we were to layer a solid, liquid and a gas, we would have the solid at the
bottom, the liquid in the middle and the gas at the top!
- Water vapor (gas state) would be less dense than water (liquid state).
- The density of a pure substance is unique to that substance. The mass to volume
ratio of a material is constant. This means that whether you have a cup of salt
water or a bathtub full of salt water the density of salt water is the same if the mass
to volume ratio is the same! If the mass of a substance increases, the volume will
also increase.
Displacement – the space an object takes up when it is placed in a fluid. For
example, if you had a full glass of water and you wanted to put a piece of wood in
it, some of the water would pour out of the glass. The wood has “displaced” some
of the water and we can use the displaced water to figure out how much space the
wood took up!
Density = mass / volume
The density of a solid is given in g/cm3
The density of a liquid in g/mL
Students should be able to manipulate the Density formula to solve for mass and
volume!
Sample Problems
1. Find the density of a 10 g mass of a substance that has a volume of 2.0 cm3.
D = m/V
D = 10 g / 2.0 cm3
D = 5.0 g/cm3
2. What is the density of 25 g of a substance placed in 10 L of a liquid?
D = m/V
D = 25 g / 10 L
D = 2.5 g/L
3. The density of a substance is 9 g/cm3. If the object has a mass of 27g, what is
the volume?
V = m/D
V = 27g / 9 cm3
V = 3 cm3
4. What is the mass of a substance that has a density of 50 g/mL and a volume of 2
mL?
m=DxV
m = 50 g/mL x 2 mL
m = 100 g
Assignment: Practice Problems
Page 312 # 1, 2,3
Page 313 # 1,2,3
Page 314 # 1,2,3
Increase Temperature = Decreased Density
Decrease Temperature = Increased Density
- According to the PTM, increasing temperature will cause the particles in a
substance to gain energy and spread out, thus taking up more space. This results in
it being less dense.
Hot Air Balloons – the inside of the balloon is heated. As the particles gain energy
from the heat, the air particles inside the balloon begin to move around and spread
further apart from one another. As the density of the air in the balloon decreases, it
becomes less dense than the air around the balloon and will rise. The pilot can
control the balloon by controlling the heat that enters the balloon.
Tire pressure – as temperatures decrease in winter months the particles inside the
air in the tires lose energy and take up less space. The density of the air has
decreased and the tired deflates a little. In summer, the heat causes the particles to
gain energy and expand, inflating the tire.
Drying wood – freshly cut wood is much heavier than wood that has been dried out
because of the amount of water in the tree. Once the tree is left to dry, the water
particles in the wood evaporate and are replaced with air. The air is less dense than
water, making the dry wood less dense than fresh wood.
Swimming – Easier to float in salt water than fresh water because the density of
salt water is gr eater than that of fresh water and can support more of your body
weight!
Submarines – submarines are able to sink and come back to the surface by taking
on or getting rid of water. Again, as the submarine gets rid of water, the space is
replaced with air which is less dense, allowing the submarine to rise to the surface.
Chapter 9
Force – anything that causes a change in the motion of an object, such as a push or
a pull
Balanced Forces – balanced forces are equal in strength but opposite in direction
and there is no movement.
Examples of balanced forces:
Unbalanced Forces – unbalanced forces are unequal in strength and cause a change
in speed or direction. An object will continue in the direction toward which the
greatest force is pushing.
Newton – we measure force in Newton (N)
Weight – A measure of the force (pull) of gravity on an object
Mass – the amount of matter in a substance
Weight looks at the gravity on an object and will change if the gravitational forces
change – for example, your mass on earth would be different if you landed on the
moon, on Jupiter or anywhere else in the universe. Mass, however, does not
change no matter where you are in the universe.
- The higher the weight in Newton, the higher the force of gravity. Which of the
following planets would have the least amount of gravity? It would be Mercury
because it has the lowest weight in Newton.
Planet
Earth
Mercury
Venus
Weight (Newton)
680
240
572
- Buoyancy is the upward force of an object submerged or floating on fluids.
- A buoyant force pushes away from the center of the earth; gravity will pull you
toward the center of the earth. The forces work against each other.
- An object that floats has NEUTRAL BUOYANCY. This happens when the force
pulling down (gravity) equals the force pushing up (buoyancy).
- Floating does not necessarily mean directly on top of the water… an object may
float in the water or under the surface and still have neutral buoyancy.
- An object will sink into the fluid until it has displaced a volume of fluid that has
the same weight as the object. Then, it will float.
- If it cannot displace enough water to match its weight, the object will continue to
sink because its gravity force is larger than its buoyant force. These are unbalanced
forces.
- If the density of an object is greater than the density of the fluid you put it in, then
the object is going to sink!
- Average Density – the total mass of all substances that make up an object divided
by the total volume.
- Because of average density, objects that would normally sink are able to float.
Example: Boats are made of steel which has a density of 9.0 g/cm3. As long as
they have large, hollow hulls that can fill with air (which has a density of 0.0012
g/cm3) it will be able to float. We can look at the average density of the boat filled
with air which will be less dense than the water in which the ship will be placed in!
Wooden boat versus water logged stick
- Wooden boat will have an average density of wood + air and will have a lower
average density than the water it is placed in so it will float. A water logged stick
has the average density of wood + water which will have a higher average density
than the water it is placed in and will sink.
Metal block versus Metal boats
- A metal block is a solid block that has a higher density than water so it will sink.
We are not combining the density of it with anything else, so it is not able to use
the average density idea in order to sink. When we build the metal boat, we are
now combining the density of the metal with air that will fill the boat and the
average density is smaller and will be able to float.
Sealed empty plastic bottle versus plastic bottle full of water
- a sealed, empty bottle is not really empty. It has air trapped inside of it. The
average density of the bottle + air will be small so it will float. The bottle full of
water has an average density of bottle + water will be higher than the density of the
water it will be placed in so it will sink.
- Personal floatation devices – when worn, they allow your body to have a lower
average density and you are then able to float in the water and not drown
- Submarines – allow water to flow in and out. When the weight of the submarine
+ water is greater than the buoyant force, it will sink. When the water is let out of
the submarine, it weighs less, is less dense and will come to the surface.
- Hot air balloons – the air inside the balloon heats up and spreads out, forcing
some of the particles out of the balloon. The air inside of the balloon then becomes
less dense than the air surrounding the outside of the balloon allowing the balloon
to rise.
- Pressure is the force acting on a certain area of a surface. When you press your
hands against a wall you are applying pressure on that area of the wall!
- The unit for measuring pressure is called the Pascal (Pa).
- Atmospheric pressure – the amount of force that is exerted by the weight of the
atmosphere.
- The larger the force, the greater the pressure.
- The smaller the area, the greater the pressure.
Pressure = Force / Area
- Students should be able to manipulate the formula to solve for F and A as well.
- Students should recognize that N/m2 = Pa
- Area – the amount of space something takes up, calculated in m2
Sample Problems
1. An aquarium is filled with water that weights 10 000 N. If the base of the
aquarium has an area of 1.6 m2, what pressure does the water exert on its base?
P=F/A
P = 10 000 N / 1.6 m2
P = 6250 Pa
2. If the pressure is 101 200 Pa and you are holding your hand out, the atmosphere
is exerting a force on your hand. If the area of your palm is 0.006 m2, calculate the
force on your hand.
F=PxA
F = 101 200 Pa x 0.006 m2
F = 607 N
3. The weight of water in a glass is 4.9 N. If the water is exerting a pressure of
1700 Pa on the bottom of the glass, what is the area of the bottom of the glass?
A=F/P
A = 4.9 N / 1700 Pa
A = 0.0029 m2
Assignment
Practice problems on page 351 – 353
Hydraulic system – hydraulics is the study of pressure in liquids. Hydraulic
systems are systems that apply force on liquids to move other objects.
Since water has a definite volume, it is incompressible. This means it cannot be
squeezed into smaller containers. For example, ALL OF the water in a large glass
cannot be forced into or compressed into a smaller glass.
The liquid in a hydraulic system must be in tubes, hoses or pipes which cause
pressure to be exerted equally in all directions and eventually will push through the
end of the system forcing something to move.
Examples of hydraulic systems are dentist or hair dresser chairs and dump trucks,
Pneumatic system – pneumatics is the study of pressure on gases. Pneumatic
systems are systems that apply force on gases to move other objects.
Gases have an indefinite volume and can therefore be compressed or forced into
smaller containers. This creates a build-up of air pressure that when released
pushes air particles apart quickly creating a strong, steady force that can perform
powerful tasks.
Examples of pneumatic systems are jackhammers, dentist drills and air brakes in
trucks and buses.
Hydraulics versus Pneumatics Chart
Property
State
Volume
Pressure
Hydraulic System
Liquid
Definite
Not compressible
Pneumatic System
Gas
Indefinite
Compressible
Pascal was a 17th century scientist that studied pressure.
Pascal’s Law states that pressure applied to an enclosed fluid is transmitted with
equal force throughout the entire container. This is the basics of both the hydraulic
and pneumatic systems
Examples of Pascal’s Law can be found when we use:
1. Car lift or hoist
2. Hydraulic jacks
3. Automobile breaking systems
4. Air compressors
5. Squeezing a tube of toothpaste
- If we increase the pressure on a gas, we decrease the volume of the gas.
However, the temperature must be constant.
* We see this in aerosol cans, paint ball guns, spray paint, whipped cream,
propane tanks… These are highly pressurized, which allows us to fit a
large volume into a small can!
-If we increase the temperature on a gas, we increase the volume. However, the
pressure is constant.
* We see this in hot air balloons or gas cans on a hot day. When its warmer,
the gas particles move further apart causing the air/gas to increase in
volume.
- If we increase the temperature of a gas, we increase the pressure. However, the
volume is constant.
* If we heat sealed containers eventually the containers will explode because
we have increased the pressure of the fluid.