Science Tests and You
Volume 3 Issue 2
Fluids
7.1 The Many Uses of Fluids
- A fluid is any substance that flows.
- Fluids have many uses, including holding and transporting other materials.
- Substances in their fluid form can be shaped and then cooled to become solids.
One of the reasons why fluids are important is that they make it easier to transport, process, and use
different kinds of materials, even if these materials are solids.
A mixture of solids and water is called a slurry.
Slurry technology - the transport of solids in water - is important in many applications. Hyrdoseeding
is the process of spraying a slurry of seeds, fertilizer, and sawdust to plant difficult-to-reach areas.
- Fluids can hold other materials - The watery cytoplasm in your cells holds the organelles that allow a
cell to expand, grow, and replicate.
- Fluids become solids. Remember the concrete bottle that we made in class.
- Fluids have other uses - Oil in a car is used to reduce friction, and to reduce noise, heat and wear.
Some fluids, such as gases, can be forced into a smaller volume, such as a scuba tank.
10.2 Fluids and the Particle Theory of Matter.
- Matter is anything that has mass and volume.
- The particle theory of matter is a way of explaining the behaviour of matter..
- Solids hold a definite shape because their particles are packed closely together and vibrate in one
place.
- Liquids can flow and take the shape of their container because their particles have partly overcome
their attraction for each other.
- Gases can flow and spread out because their particles are far apart and have overcome their
attraction for each other.
Matter is anything that has mass and volume.
Mass is a measure of how much matter there is in a substance.
Volume is a measure of how much space a substance takes up.
6 Point of the particle theory
1. All matter is made up of tiny particles.
2. All particles are in motion.
3. All particles of one substance are identical.
4. Temperature affects the speed at which particles move.
5. In liquids, and solids, the particles are close together and have strong forces of attraction between
them.
6. In a gas, there are spaces between the particles.
- Liquids and and gases can flow
- When a substance increases in temperature, the particles heat up and move farther apart. This results
in the substance expanding. Thermal expansion is an increase in the volume of a substance in a
response to an increase in temperature.
8.1 Viscosity and the Effects of Temperature
- Viscosity is the resistance of a fluid to flow. Different fluids have different viscosity.
- As the temperature of a liquid decreases, the viscosity increases. As the temperature of a gas
decreases, the viscosity decreases.
- Flow rate is a measure of the speed at which a fluid flows from one point to another. The higher the
flow rate, the lower the viscosity.
The amount of mass contained in a given volume is called density. Density describes how closely
packed together the particles are in a substance.
8.2 Density and Buoyancy
- Density is the ration between mass and volume.
- The solid state of a substance is usually denser than the liquid state. The liquid state is denser than
the gas state.
- The upward force exerted by a fluid is called the buoyant force.
- Archimedes’ principle states that the buoyant force on an object is equal to the weight of the fluid
displaced by the object.
- If the density of a substance is greater than the density of the fluid, the substance will sink.
- If the density of a substance is less than the density of the fluid, the substance will float.
- if the density of a substance is the very same as the density of the fluid, the substance will “hover” in
place.
To calculate density we use the expression D = M/D (Density equals Mass divided by Volume)
Forces in fluids - A force is a push, or pull that acts on an object. The measure of a unit of force is the
Newton (N). One newton is equal to the force you would exert to hold a baseball.
Buoyancy is the tendency of an object in a fluid to rise or sink due to density differences with its
surroundings.
- The upward force exerted by a fluid is called the buoyant force.
- The Archimedes Principle states that the buoyant force on an object is equal to the weight of the fluid
displaced by the object.
- Transportation technologies such as hot air balloons, airships, and research platforms use the concept
of buoyancy in their design.
- A plimsoll line shows how heavily a ship can be safely loaded in different water conditions. (Salt
water has a greater density than fresh water. Thus, a boat will “sit” in the water lower in fresh water than
in salt water)
8.3 Pressure in Fluids
- Pressure is the amount of force applied to a given area.
- Pressure increases with depth.
- Fluids will naturally move from an area of higher pressure to an area of lower pressure.
- Gases can be compressed easily. Liquids are very difficult to compress.
The air in the middle ear (The Eustachian tube) is sometimes at a different pressure than the air in the
outer ear (ear canal). A sudden change in air pressure results in your ears “popping”.
Pressure in a fluid also changes with its depth. The weight of the water in the upper part of a swimming
pool, presses down on the water in the lower part of the pool.
Remember looking at the water coming out the three holes of the tropicana jug. The water came out
further in the bottom hole due to the increased pressure from the water above.
If a fluid is allowed to move, it will always go from an area of higher pressure to an area of lower
pressure.
The pressure exerted by a fluid is the sum of all the forces exerted by the individual particles in the fluid.
When the temperature increases, the particles bump into each other, if the temperature continues to
increase, and the volume of its container cannot, then an explosion may result.
Compression is a decrease in volume caused by a force
Compressibility is the property of being able to be compressed.
Incompressible means that something cannot be compressed easily - Liquids are said to be
incompressible.
9.1 Fluid Systems.
- Pascal’s law states that when force is applied to an enclosed fluid, the increase in pressure is
transmitted equally to all parts of the fluid.
- There are both natural fluid systems and manufactured fluid systems.
- Hydraulic systems are fluid systems that use liquid, such as water or oil, as the enclosed fluid.
- Pneumatic systems are fluid systems that use gas (usually air) as the enclosed fluid.
- Fluids can be transported within a fluid system by pumps and valves.
- A fluid system is a group of parts, including at least one fluid, that interact with each other and
function together as a whole.
- A hoist uses two pistons of different sizes to create pressure to lift a vehicle.
- A piston is a disk that moves inside a cylinder.
A pneumatic system uses a gas under pressure to transmit a force - Two advantages are safety and
cost. Compressed air is safe to use, as the devices to not create sparks within the system They are also
more reliable over a larger temperature range than a hydraulic system.
- A hyperbaric chamber uses gases under pressure to help divers suffering from decompression
sickness.
- A pump is a device that moves a fluid through or into something.
- The Archimedes Screw pump continuously raises water upwards as it rotates.
A valve is a device that controls the flow of fluids. A valve is used to assist in inflating soccer balls. (that
little metal thing that goes into the ball)
9.2 The Impact of Fluid Spills
- Fluid spills on water are generally more environmentally damaging than fluid spills on land.
- The majority of fluid spills occur on land and these spills are carried to rivers and oceans by run-off.
- Methods of cleaning up oil spills include booms, skimmers, sorbents, dispersants, burning, and
bioremediation.
- Everyone can help prevent fluid spills.
The Exxon Valdez dumped more than 30 million litres of oil off of the coast of Alaska. After spending
$2.5 billion and 20 years later, there is still more than 100 000L of oil embedded in the sandy shoreline.
When oil is added to water it floats on top. Oil has a density of .88g/ml (fresh water has a density of
1g/ml, salt water = 1.02g/ml) This makes clean up easier than if it had a greater density.
The extent of the damage caused by an oil spill depends on many factors such as the type of oil, the
location of the spill, and the size of the spill.
READ Table 9.1 on page 253 which talk about the results of oil spills.
There are many clean-up methods that can be used to clean up an oil spill.
READ Table 9.2 on page 254 which discusses the many different methods of cleaning up oil spills.
The environmental impact of a spill on land is much more localized than that of a spill on water. This is
due to the fact that the spill does not spread as quickly as it would do on water. The methods for
cleanup are similar than the methods used to cleanup spills on water.
There are other types of fluid spills that can cause environmental problems. In one example listed in
your text, 11 000L of dry-cleaning fluid spilled into the St. Clair river in Sarnia, Ontario in 1985.
The cost of cleanup of a fluid spill ranges from $20-$200 for every litre spills. Remember the Valdez
spilled 30 million litres - Yikes!