Grade 8. A fluid is anything substance that flows Honey, water, and lava are all fluids – but so are gasses such as oxygen and carbon dioxide We use fluids.

FluidsGrade 8

A fluid is anything substance that flows Honey, water, and lava are all fluids – but so

are gasses such as oxygen and carbon dioxide

We use fluids to help us improve our lives

The Many Uses of Fluids

Fluids can transport solids A mixture of water and solids is called a

slurry The paper that you write on was once a

slurry of wood pulp and water Hydroseeding is the process of spraying a

slurry of seeds, fertilizer and sawdust to plant difficult to reach areas

The Many Uses of Fluids

Fluids can hold other materials

For example, the cytoplasm in your cells hole the organelles that allow a cell to grow and replicate

Toothpaste is a fluid that holds materials designed to clean, polish and protect your teeth.

The Many Uses of Fluids

A slurry of water and cement is easy to transport. As it hardens it can be shaped to become a smooth, level concrete sidewalk

The Many Uses of Fluids

Each of these photographs show fluids in use1. How are our lives improved by each of the uses

shown2. What environmental issues are raised by each use?

The Many Uses of Fluids

Matter is anything that has mass and volume

The Particle Theory of Matter is a theory that describes matter. It explains the behaviour of solids, liquids and gasses.

Copy the 6 postulates of the theory into your booklet from page 198 in your textbook.

Fluids and The Particle Theory

The particle theory states that particles are attracted to each other. However, particles in some substances may be more attracted to particles in other substances than they are to each other

Particles in a liquid can overcome some of their attraction to each other and slide past each other. This is why liquids flow and take the shape of their containers

Fluids and The Particle Theory

Gas particles can move so quickly and are so far apart that they overcome almost all their attraction to each other. This is why gasses flow and spread out to all parts of their container.

Fluids and The Particle Theory

When the temperature of a solid, liquid or gas increase, its particles move faster and farther apart – as a result the substance expands

Thermal expansion is an increase in the volume of a substance in response to an increase in its temperature

Thermal Expansion and Contraction

Ketchup, like all liquids will flow. However, it is designed to flow slowly so it will stay on food.

Thickness or thinness of a fluid is called viscosity.

Viscosity is the resistance of a fluid to flow.

Fluids with a high viscosity do not flow as easily as fluids with a low viscosity

Viscosity and Temperature

Temperature can have a big effect on viscosity

When heat is added to a liquid, the particles move faster and move farther apart. This allows the particles to move past each other more freely

As the temperature of a liquid increases, its viscosity decreases.

The cooler the liquid, the slower it flows.

Viscosity and Temperature

Temperature affects the viscosity of gasses differently from how it affects liquids

Friction is a force that works to slow down motion as a result of surfaces rubbing against each other

The greater the rubbing, or friction between particles in any fluid, the higher the viscosity

Viscosity and Temperature

BUT in gases, the higher the temperature, the higher the friction and the higher the viscosity. The warmer the gas, the slower it flows.

As the temperature of the gas decreases, the particles slow down and collide less often, so there is less friction. The viscosity decreases.

The cooler the gas, the faster it flows.

Viscosity and Temperature

The flow rate of a fluid is a measure of speed at which a fluid flows from one point to another

The greater the viscosity, the lower the flow rate.

Viscosity and Flow Rate

The amount of mass contained in a given volume is called density

Density describes how closely packed together the particles are in a substance

A substance is most dense when it is a solid, and least dense when it is a gas

Density

Read page 216 in the textbook. Copy the three points in your booklet.

If metal has a greater density than water – how is it possible for metal boats to float on water?

Density and Buoyancy

If you consider the density of the air inside the boat and the density of all the objects in the boat, you would find that the combined density of all parts of the boat is less than the density of the water.

Density and Buoyancy

Density is the ratio of mass to volume. The unit for measuring the density of liquids is usually grams per millilitre (g/ml)

You can calculate the density if a substance by dividing its mass by its volume

Density (D) = mass (m)Volume (v)

Calculating Density

A force is a push or pull on an object – but you already knew that

We measure force in newtons (N)

One newton is approximately equal to the force that you would exert to hold up a baseball.

Forces of Fluids

Buoyancy is the tendency of an object in a fluid to rise or sink due to density differences with its surroundings,

Gravity attracts matter downwards

towards the earths centre. A fluid however exerts an opposite force that pushes matter upward. This is called the buoyant force.

Read page 220 to fill out the chart in your booklet.

Forces of Fluids

Pressure is the amount of force applied to a given area.

You may have felt the pressure of water when you swim deep in water.

Air is a fluid and it exerts pressure around you all the time. Air pressure is why your ears may “pop” when you are on a plane.

Pressure in Fluids

Air pressure changes with altitude

There is less air pressure if we travel to a higher altitude, like a mountain, because there are fewer layers of air above us and the air there is less dense.

Changes in Pressure

Pressure in fluid also changes with its depth

For example, the weight of the water in the upper part of a swimming pool presses down on the water on the lower part of the pool

The greater the dept of water, the greater the pressure at that point.

Pressure and Depth

If a fluid is allowed to move, it will always go from an area of higher pressure to an area of lower pressure

You make use of this property when you drink from a straw. Your mouth creates an area of lower pressure. The juice box is at a higher pressure, so it travels up the straw and into your mouth. Mmm.

Pressure and Fluid Flow

An increase in temperature results in an increase in pressure.

When the temperature increases, the particles move faster and hit the walls of the container with more energy

If the volume of the container cannot

increase, its pressure increases, possibly resulting in an explosion

Pressure and Temperature

Compression is a decrease in volume caused by a force

Compressibility is the property of being able to be compressed

Materials in a liquid state are said to be incompressible, which means they can not be compressed easily

Your foot compresses the air inside the soccer ball as you kick it.

Compression

A fluid system is a group of parts, including at least one fluid, that interact with each other and function as a whole.

Two examples found in nature are

Our body’s circulatory system The movement of sap in trees

Fluid Systems

Blaise Pascal made an important discovery in the mid 1600s.

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.

For example, when you squeeze a balloon in the middle and it bulges evenly at either end

Pascal’s Law

Hydraulic systems are systems that use a liquid under pressure to transmit a force and do work.

Rescue workers use hydraulic systems in the Jaws of Life to free people trapped in vehicles

Hydraulic Systems

Liquids can not be compressed. This means that when pressure is applied to a liquid in a pipe or a tube, the force can be transmitted over a distance

Hydraulic systems can multiply the force exerted by a liquid.

Read pages 242-243 to explain how a hoist works,

Hydraulic systems

A pneumatic system is a system that uses a gas, usually air, under pressure to transmit a force.

In order for a gas to be put to work in a fluid system, it must first be compressed.

Two advantages of pneumatic systems are safety and cost.

Pneumatic Systems

A pump is a device that moves a fluid through or into something.

For example, your heat pumps blood to your lungs.

Pumps

Valves are devices that control the flow of fluids

For example, turning a tap one way allows water to flow out. Turning it the other way closes off the flow of water.

Page 247 of your textbook describes 4 different types of valves.

Valves