Chapter 17 – Properties of Matter

17.1 – Properties of Solids• Density is measurement of the compactness

of a substance.– the ratio of mass and volume. – D = m/v– Units are g/mL or g/cm3

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http://www.dmturner.org/Teacher/Library/4thText/MatPart1.html

• Density describes how tightly packed the atoms or molecules are.

• Hardness measures a solid’s resistance to scratching. Diamonds are the hardest natural substance found on Earth.

http://invsee.asu.edu/nmodules/engmod/prophardness.html

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

• Also gives objects the ability to bounce and withstand impact without breaking.

• All materials have some elasticity. The most elastic are metals and rubber.

http://www.learner.org/jnorth/images/graphics/m/Muscle_RubberBand2.jpg

• Brittleness measures a material’s tendency to shatter upon impact.

• Brittleness is considered a hazardous property in the automobile industry.

• The first “safety glass,” designed to reduce the brittleness of regular glass, and was discovered by accident.

• In 1903, a French chemist dropped a glass flask. The flask was full of cracks, but surprisingly, the pieces did not scatter across the floor. The flask remained intact.

• Malleability measures a solid’s ability to be pounded into thin sheets.

• Ex: steel and aluminum

• Tensile strength is a measure of how much pulling, or tension, a material can withstand before breaking.

• Crucial in the manufacture of cables and girders used to support structures.

http://www.lotia.com/images/steel_wireropes/steel_wirerope01.jpg

17.2 – Density of Fluids

• A fluid is defined as any matter that is able to flow. Both liquids and gases are a fluid.

• The density of solids usually decreases as temp. increases because solids expand when heated. As the temp. of the solid increases, the volume increases.

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• Most materials are denser in their solid phase than in their liquid phase.

• Water is an exception. Ice is less dense than liquid water!

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• What would happen if solid water was denser?

• Ice would sink.• Many aquatic plants could no longer grow.

Animals that burrow in the mud at the bottom of ponds could not complete their life cycles.

• The climate of cities along large bodies of water would become much cooler.

17.3 – Buoyancy of Fluids• Buoyancy is a measure of the upward pressure

a fluid exerts on an object.• In the 3rd century BC, Archimedes made an

important discovery about the buoyant force. • He realized that the force exerted on an object

in a liquid is equal to the weight of the fluid displaced by the object. This relationship is Archimedes’ principle.

http://physics.weber.edu/carroll/Archimedes/principle.htm

• Buoyancy helps explain why some objects sink and others float.

• If the buoyant force is greater than its weight, the object floats.

• If the buoyant force is less, then the object will sink.

http://physics.weber.edu/carroll/Archimedes/principle.htm

• According to Charles’ law, the volume of a gas increases with increasing temperature. The volume of a gas shrinks with decreasing temperature.

http://www.grc.nasa.gov/WWW/k-12/VirtualAero/BottleRocket/airplane/aglussac.html

• Pressure is the force acting on a unit area of surface.

• Tire pressure is usually measured in units of psi.

• The SI unit for pressure is a pascal (Pa).

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• Boyle’s law states that as the pressure of a gas increases, its volume decreases. As the pressure of a gas decreases, its volume increases.

• P1V1 = P2V2

http://www.grc.nasa.gov/WWW/K-12/airplane/Animation/gaslab/chprmt.html

17.4 – Viscosity of Fluids

• Viscosity is another important property of fluids. It is a measure of the material’s resistance to flow.

Viscosity Demo

• Viscosity is determined in large part by the shape of the molecules in a liquid. Large, bumpy molecules create more friction than small, smooth molecules

• Remember that when energy is added to a liquid, the movement of the molecules increases.

• As the temp of a liquid is raised, the viscosity of the liquid decreases.

• Gases exhibit the opposite property. As you raise the temperature of a gas, it becomes more resistant to flow. As a gas gets warmer, its viscosity increases.