PROPERTIES OF MATTER

Chapter Twelve: Properties of Matter

12.1 Properties of Solids

12.2 Properties of Fluids

12.3 Buoyancy

Chapter 12.1 Learning Goals

Distinguish chemical properties from physical properties of matter.

Identify differences between crystalline and amorphous solids.

Explain how the arrangement of atoms and molecules in solids determines their properties.

Investigation 12A

Key Question:How do solids and liquids differ?

Mystery Material

12.1 Properties of Solids Different kinds of matter

have different characteristics.

Characteristics that can you observe directly are called physical properties.

Physical properties include color, texture, density, brittleness, and state (solid, liquid, or gas).

Ex. Iron is solid at room temp.

12.1 Properties of Solids A physical change is any

change in the size, shape, or phase of matter in which the identity of a substance does not change.

For example, when water is frozen, it changes from a liquid to a solid.

12.1 Properties of Solids Properties that can only be

observed when one substance changes into a different substance are called chemical properties.

Any change that transforms one substance into a different substance is called a chemical change.

Ex. If you leave a nail outside, it rusts.

Iron reacts with oxygen to form iron oxide.

12.1 Properties of SolidsThe density of a solid

material depends on two things:

1. the individual mass of each atom or molecule,

2. how closely the atoms or molecules are packed together.

Carbon atoms in diamond are packed very tightly.

12.1 Properties of Solids Paraffin wax is also

mostly carbon, but its density is only 0.87 g/cm3.

Paraffin’s carbon atoms are mixed with hydrogen atoms in long molecules that take up more space.The density of paraffin

is low compared to diamond.

12.1 Properties of SolidsThe atoms or molecules in a solid

are arranged in two ways.

1. If the particles are arranged in an orderly, repeating pattern, the solid is crystalline.

2. If the particles are arranged in a random way, the solid is amorphous.

12.1 Properties of Solids Examples of

crystalline solids include salts, minerals, and metals.

12.1 Properties of Solids Metals don’t

look like “crystals” because solid metal is made from very tiny crystals fused together in a jumble of different orientations.

12.1 Properties of Solids The atoms or

molecules in amorphous solids are randomly arranged.

Examples of amorphous solids include rubber, wax, and glass.

12.1 Mechanical properties

“Strength” describes the ability of a solid object to maintain its shape even when force is applied.

12.1 Mechanical properties

Tensile strength is a measure of how much stress a material can withstand before breaking.

12.1 Mechanical properties

Hardness measures a solid’s resistance to scratching.

How might you compare the hardness of these two metals?

12.1 Mechanical properties

Elasticity describes a solid’s ability to be stretched and then return to its original size.

Brittleness is defined as the tendency of a solid to crack or break before stretching very much.

12.1 Mechanical properties

A ductile material can be bent a relatively large amount without breaking.

The ductility of many metals, like copper, allow then to be drawn into wire.

12.1 Mechanical properties

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

Aluminum is a highly malleable metal.

12.1 Mechanical propertiesAlmost all solid materials expand as the temperature increases.

The increased vibration makes each particle take up a little more space, causing thermal expansion.

Sidewalks and bridges have

grooves that allow for thermal expansion.

Chapter Twelve: Properties of Matter

12.1 Properties of Solids

12.2 Properties of Fluids

12.3 Buoyancy

Chapter 12.2 Learning Goals

Explain how pressure is created in fluids.

Discuss differences between the density of solids and fluids.

Apply Bernoulli’s principle to explain how energy is conserved in fluids.

12.2 Properties of Fluids A fluid is defined

as any matter that flows when force is applied.

Liquids like water or silver are kinds of fluid.

12.2 PressureA force applied to a fluid creates pressure.

Pressure acts in all directions, not just the direction of the applied force.

12.2 Forces in fluidsForces in fluids are more complicated than forces in solids because fluids can change shape.

12.2 Units of pressure

The units of pressure are force divided by area.

One psi is one pound per square inch.

12.2 Units of pressureThe S.I. unit of force is the pascal.

One pascal (unit of force) is one newton of force per square meter of area (N/m2).

12.2 PressureIf your car tires are

inflated to 35 pounds per square inch (35 psi), then a force of 35 pounds acts on every square inch of area inside the tire.

What might happen if you over-inflate a tire?

12.2 PressureOn the microscopic

level, pressure comes from collisions between atoms.

Every surface can experience a force from the constant impact of trillions of atoms.

This force is what we measure as pressure.

12.2 PressureIn a car engine high pressure is created

by an exploding gasoline-air mixture.

12.2 Energy conservation and

Bernoulli’s PrincipleStreamlines are imaginary lines drawn to show the flow of fluid.

Bernoulli’s principle tells us that the energy of any sample of fluid moving along a streamline is constant.

12.2 Bernoulli’s Principle

Bernoulli’s principle says the three variables of height, pressure, and speed are related by energy conservation.

12.2 Three Variables and Bernoulli’s Principle

If one variable increases along a streamline, at least one of the other two must decrease.

For example, if speed goes up, pressure goes down.

12.2 The air foil

One of the most important applications of Bernoulli’s principle is the airfoil shape of wings on a plane.

When a plane is moving, the pressure on the top surface of the wings is lower than the pressure beneath the wings.

The difference in pressure is what creates the lift force that supports the plane in the air.

12.2 Hydraulics and Pascal’s Principle

Hydraulic lifts and other hydraulic devices use pressure to multiply forces and do work.

The word hydraulic refers to anything that is operated by a fluid under pressure.

Hydraulic devices operate on the basis of Pascal’s principle, named after Blaise Pascal.

12.2 Hydraulics and Pascal’s Principle

Pascal’s principle states that the pressure applied to an incompressible fluid in a closed container is transmitted equally in all parts of the fluid.

An incompressible fluid does not decrease in volume when pressure is increased.

12.2 Hydraulics and Pascal’s Principle

A small force exerted over a large distance is traded for a large force over a small distance.

12.2 Pressure

Pressure is force divided by area.

12.2 ForceYou can calculate the force exerted if you know the pressure and area.

Solving Problems

On a hydraulic lift, 5 N of force is applied over an area of 0.125 m2.

What is the output force if the area of the larger cylinder is 5.0 m2?

1. Looking for: …output force

2. Given …input force = 5 N; input area = .125

m2 ; output area = 5 m2

3. Relationships: Pressure = ForceForce = P x A

Area

Solving Problems

4. Solution Solve for pressure using input

force. Pressure = 5 N = 40 N/m2

.125m2

Use Pascal’s law principle and use equivalent pressure to solve for output force.

Force = 40 N x 5 m2 = m2

Solving Problems

200 N

12.2 Viscosity

Viscosity is the property of fluids that causes friction.

Viscosity is determined in large part by the shape and size of the particles in a liquid.

12.2 Viscosity and temperature

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

Increasing the kinetic energy of the substance allows the particles to slide past one another more easily.

Investigation 12C

Key Question:What is the maximum load a boat can hold

before sinking?How is the maximum load affected by the

density of the water in which the boat floats?

Density of Fluids

Chapter Twelve: Properties of Matter

12.1 Properties of Solids

12.2 Properties of Fluids

12.3 Buoyancy

Chapter 12.3 Learning Goals

Define buoyancy.

Explain the relationship between density and buoyancy.

Discuss applications of Archimedes’ principle.

Investigation 12B

Key Question:Can you make a clay boat?

Buoyancy of Fluids

12.3 Buoyancy is a forceBuoyancy is a measure of the upward force a fluid exerts on an object that is submerged.

The water in the pool exerts an upward force that acts in a direction opposite to the boy’s weight.

12.3 Volume and buoyancyThe strength of the buoyant force on an

object in water depends on the volume of the object that is underwater.

As you keep pushing downward on the ball, the buoyant force gets stronger and stronger. Which ball has more volume underwater?

12.3 Weight and buoyancyWeight is a force, like any

other pushing or pulling force, and is caused by Earth’s gravity.

It is easy to confuse mass and weight, but they are not the same.

Weight is the downward force of gravity acting on mass.

What is the rock’s weight?

What is the rock’s mass?

12.3 Weight and buoyancyIn the third century BC, a

Greek mathematician named Archimedes realized that buoyant force is equal to the weight of fluid displaced by an object.

A simple experiment can be done to measure the buoyant force on a rock with a spring scale when it is immersed in water.

12.3 Weight and buoyancyIn air the buoyant

force on the rock is 29.4 N.

When the rock was submerged, the scale read 19.6 N.

The difference is a force of 9.8 N, exactly the amount of force the displaced water exerts.

12.3 Weight and buoyancy

These blocks are the same total volume. Which block has more buoyant force acting on it?Which block weighs more in air?

12.3 Weight and buoyancyBuoyancy explains why some objects sink and others float.

Whether an object sinks or floats depends on how the buoyant force compares with the weight.

12.3 Density and buoyancyIf you know an object’s density you can quickly predict whether it will sink or float.

Which ball will sink in water?Which ball will float in water?

12.3 Density and buoyancyAverage density helps determine whether objects sink or float.

An object with an average density GREATER than the density of water will sink.

An object with an average density LESS than the density of water will float.

12.3 Density and buoyancy

What can you say about the average density of these blocks?

12.3 Density and buoyancyWhen they are completely underwater, both balls have the same buoyant force because they displace the same volume of water.

However, the steel ball has more weight since it has a higher density.

12.3 Boats and average densityUse your understanding of

average density to explain how steel boats can be made to float.

12.3 Boats and average densityIf you have seen a loaded cargo ship,

you might have noticed that it sat lower in the water than an unloaded ship nearby.

A full ship has more mass than an empty ship.

This means a full ship must displace more water (sink deeper) to make the buoyant force large enough to balance the ship’s weight.

Investigation 12C

Key Question:What is the maximum load a boat can hold

before sinking?How is the maximum load affected by the

density of the water in which the boat floats?

Density of Fluids

The HullThere are many

different types of boats, but all have one thing in common—the hull.

The hull is the main body of the boat. It displaces the water that provides the upward buoyant force. It also provides stability.