Properties of Solids and Fluids

Density

• Density is a property that describes the relationship between mass and volume.

V

mD Density (g/cm3)

Mass (g)

Volume (cm3)

• Density describes how tightly packed the atoms or molecules in a substance.

• The density of a pure substance is the same regardless of the form.

Note: Both the paper clip and bike cable are made of steel

Calculate the density

• What is the density of a piece of wood that has a mass of 25 grams and a volume of 29.4 cm3?

• D (density) = mass (mass in grams) / V (volume in cm3

• D = 25 grams/ 29.4 cm3 = .850 g/cm3

Properties of Solids

• Hardness: measure of solid’s resistance to scratching.

• Elasticity: measure of a solid’s ability to be stretched and return to its original size.

• Brittleness: measure of solid’s ability to shatter upon impact

• Malleability: measure of solid’s ability to be pounded into thin sheets

• Tensile strength: measure of how much pulling a solid can withstand without breaking.

Fluids: Liquids and Gases

ViscosityBuoyancy

Archimede’s Principle

Density of Fluids

• Since the atoms in a liquid are not as neatly stacked as the atoms in a solid are, the liquid tends to take up more space.

• As a result, liquids are typically less dense than solids.

That Crazy Water!• Water is unusual and an

exception. Ice (solid form) is less dense than the liquid form. Therefore, ICE FLOATS.

• Frozen water molecules freeze into ice crystals that are mostly empty space. The molecules are more tightly packed in water’s liquid form.

Buoyancy and Archimedes Principle

• A buoyant force is an upward force exerted on an object by a fluid in which the object is immersed. When an object is placed in a fluid, the object displaces some of the fluid. The volume of the fluid displaced is equal to the volume of the object.

• Archimede’s principle - an object in a fluid is acted on by a buoyant force equal to the weight of the fluid displaced by the object

• Demonstration

Viscosity

• Viscosity is a property of gases and liquids.• Viscosity is a measure of the material’s

resistance to flow.• High viscosity fluids take longer to pour from

their containers than low viscosity fluids.

• Demonstration

Why are some liquids more viscous than others?

• Viscosity is determined by the shape and the size of the molecules in the liquid.

• Larger molecules create more friction than small, smooth molecules.

• Liquids with large molecules will flow at a slower rate than liquids made up of small molecules.

Gases

Charles’ LawBoyle’s Law

Pascal’s PrincipleBernoulli’s Principle

Density of gases

• Gases are always less dense than solids or liquids

• Density of gases depends upon the molecular weight of the gas particles

• If a gas is lighter than air, it rises above the air and if it is heavier it sinks through the air to the ground

Behavior of Gases

• Charles’ Law says that a volume of a gas will increase with increasing temperature.

• As the air in a hot air balloon is heated, volume of the balloon increases. As a result, the density of the air inside the balloon decreases.

• A hot air balloon will rise because the density of the air inside the balloon is less dense than the air surrounding the balloon.

Boyle’s Law

• If you squeeze the same amount of gas in a smaller container, the gas particles collide with the walls of the container more often, increasing the pressure.

• Boyles law says as thepressure of a gas increasesits volume decreases proportionally.

Pressure

• Pressure is the force of the fluid acting on a surface.

• As you increase the movement of the

particles, the pressure increases.

• The unit of pressure is a pascal (Pa)

Pascal's Principle• Pressure is transmitted undiminished or

unchanged throughout an enclosed static fluid.

If the bottle is filled to the top with water, then any pressure exerted on the water is transmitted undiminished to the bottom of the bottle, which has a larger area. The multiplied force can pop the bottom out of the bottle.

Bernoulli’s Principal

• States that as the velocity of a fluid increases the pressure exerted by the fluid decreases.

• Demonstration

Airplane Wing

• The air across the top of a conventional airfoil experiences constricted flow lines and increased air speed relative to the wing.

This causes a decrease in pressure on the top according to the Bernoulli equation and provides a lift force.