2. Chapter Twelve: Properties of Matter
12.1 Properties of Solids
12.2 Properties of Fluids
12.3 Buoyancy

3. 10.1 The Nature of Matter
Matter is a term used to describe anything that has mass and takes up space.
Greek philosophers Democritus and Leucippus proposed that matter is made of tiny particles called atoms.
Atoms were an idea that few believed.
The first evidence was called Brownian motion for Robert Brown, who first noticed the jerky motion of tiny particles.

4. 10.1 Elements
An element is a pure substance that cannot be broken down into other substance by chemical or physical means.
All of the matter you are ever likely to experience is made from one or more elements in nature.

5. 10.1 Elements
For example, water can be broken down into its elements, hydrogen and oxygen, when energy is added.

6. 10.1 Atoms
A single atom is the smallest particle that retains the chemical identity of the element.

7. 10.1 Compounds and elements
Compounds are two or more different elements chemically bonded together.

8. 10.1 Examples of compounds
Compounds contain more than one type of atom joined together.

9. 10.1 Molecules
A molecule is a group of two or more atoms joined together chemically.

10. 10.1 Mixtures
Many substances you encounter are a mixture of different elements and compounds.
How many atoms are in this mixture?
How many molecules are in this mixture?

11. 10.1 Elements, compounds, and mixtures
Can you distinguish between atoms and molecules in these images?

12. 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.

13. 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.

14. 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.

15. 12.1 Properties of Solids
The density of a solid material depends on two things:
the individual mass of each atom or molecule,
how closely the atoms or molecules are packed together.
Carbon atoms in diamond are packed very tightly.

16. 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.

17. 12.1 Properties of Solids
The atoms or molecules in a solid are arranged in two ways.
If the particles are arranged in an orderly, repeating pattern, the solid is crystalline.
If the particles are arranged in a random way, the solid is amorphous.

18. 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.

19. 12.1 Mechanical properties
“Strength” describes the ability of a solid object to maintain its shape even when force is applied.

20. 12.1 Mechanical properties
Tensile strength is a measure of how much stress a material can withstand before breaking.

21. 12.1 Mechanical properties
Hardness measures a solid’s resistance to scratching.
How might you compare the hardness of these two metals?

22. 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.

23. 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.

24. 12.1 Mechanical properties
Malleability measures a solid’s ability to be pounded into thin sheets.
Aluminum is a highly malleable metal.

25. 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.

26. 12.2 Pressure A force applied to a fluid creates pressure.
Pressure acts in all directions, not just the direction of the applied force.

27. 12.2 Forces in fluids
Forces in fluids are more complicated than forces in solids because fluids can change shape.

28. 12.2 Units of pressure
The units of pressure are force divided by area.
One psi is one pound per square inch.

29. 12.2 Units of pressure The 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).

30. 12.2 Pressure
If 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?

31. 12.2 Pressure
On 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.

32. 12.2 Pressure
In a car engine high pressure is created by an exploding gasoline-air mixture.

33. 12.2 Energy conservation and Bernoulli’s Principle
Streamlines 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.

34. 12.2 Bernoulli’s Principle
Bernoulli’s principle says the three variables of height, pressure, and speed are related by energy conservation.

35. 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.

36. 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.

37. 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.

38. 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.

39. 12.3 Buoyancy is a force
Buoyancy 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.

40. 12.3 Volume and buoyancy
The 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?

41. 12.3 Weight and buoyancy
Weight 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?

42. 12.3 Weight and buoyancy
In 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.

44. 12.3 Weight and buoyancy
In air the buoyant force on the rock is 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.

45. 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?

46. 12.3 Weight and buoyancy
Buoyancy explains why some objects sink and others float.
Whether an object sinks or floats depends on how the buoyant force compares with the weight.

47. 12.3 Density and buoyancy
If 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?

48. 12.3 Density and buoyancy
Average 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.

49. 12.3 Density and buoyancy
What can you say about the average density of these blocks?

50. 12.3 Density and buoyancy
When they are completely underwater, both balls have the same buoyant force because they displace the same volume of water.

52. 12.3 Boats and average density
Use your understanding of average density to explain how steel boats can be made to float.

53. 12.3 Boats and average density
If you have seen a loaded cargo ship, you might have noticed that it sat lower in the water than an unloaded ship nearby.
This means a full ship must displace more water (sink deeper) to make the buoyant force large enough to balance the ship’s weight.