12. 1 Properties of Solids
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12.1 Properties of Solids
Different kinds of matter have different characteristics.
A physical change is any change in the size, shape, or phase of matter in which the identity of a substance does not change.
Properties that can only be observed when one substance changes into a different substance are called chemical properties.
The density of a solid material depends on two things:
Paraffin wax is also mostly carbon, but its density is only 0.87 g/cm3.
The atoms or molecules in a solid are arranged in two ways.
Examples of crystalline solids include salts, minerals, and metals.
Metals don’t look like “crystals” because solid metal is made from very tiny crystals fused together in a jumble of different orientations.
The atoms or molecules in amorphous solids are randomly arranged.
“Strength” describes the ability of a solid object to maintain its shape even when force is applied.
Tensile strength is a measure of how much stress a material can withstand before breaking.
Hardness measures a solid’s resistance to scratching.
Elasticity describes a solid’s ability to be stretched and then return to its original size.
A ductile material can be bent a relatively large amount without breaking.
Malleability measures a solid’s ability to be pounded into thin sheets.
Almost all solid materials expand as the temperature increases.
A fluid is defined as any matter that flows when force is applied.
A force applied to a fluid creates pressure.
Forces in fluids are more complicated than forces in solids because fluids can change shape.
The units of pressure are force divided by area.
The S.I. unit of force is the pascal.
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.
On the microscopic level, pressure comes from collisions between atoms.
In a car engine high pressure is created by an exploding gasoline-air mixture.
Streamlines are imaginary lines drawn to show the flow of fluid.
Bernoulli’s principle says the three variables of height, pressure, and speed are related by energy conservation.
If one variable increases along a streamline, at least one of the other two must decrease.
One of the most important applications of Bernoulli’s principle is the airfoil shape of wings on a plane.
Viscosity is the property of fluids that causes friction.
As the temperature of a liquid increases, the viscosity of a liquid decreases.
Buoyancy is a measure of the upward force a fluid exerts on an object that is submerged.
The strength of the buoyant force on an object in water depends on the volume of the object that is underwater.
Weight is a force, like any other pushing or pulling force, and is caused by Earth’s gravity.
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.
In air the buoyant force on the rock is 29.4 N.
Buoyancy explains why some objects sink and others float.
If you know an object’s density you can quickly predict whether it will sink or float.
Average density helps determine whether objects sink or float.
When they are completely underwater, both balls have the same buoyant force because they displace the same volume of water.
Use your understanding of average density to explain how steel boats can be made to float.
If you have seen a loaded cargo ship, you might have noticed that it sat lower in the water than an unloaded ship nearby.
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