Matter

Chapter Twelve: The Physical Properties of Matter

• 12.1 Density

• 12.2 Buoyancy

• 12.3 Properties of Materials

12.3 Pressure

• A fluid is a form of matter that flows when any force is applied, no matter how small.

• Liquids are one kind of fluid, gases are another.

12.3 Pressure

• A force applied to a fluid creates pressure.

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

12.3 Pressure

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

12.3 Pressure

• The units of pressure are force divided by area.

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

12.3 Pressure

• The pressure inside your tire is what holds your car up.

Which units are normally seen on car tires?

12.3 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.

12.3 Pressure• In a car engine high pressure is created by an

exploding gasoline-air mixture. • This pressure pushes the cylinders of the engine

down, doing work that moves the car.

12.3 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.

12.3 Energy conservation and Bernoulli’s Principle

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

12.3 Energy conservation 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.

12.3 Energy conservation and Bernoulli’s Principle

• 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.

12.3 Mechanical properties

• When you apply a force to an object, the object may change its size, shape, or both.

12.3 Mechanical properties

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

12.3 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.

12.3 Mechanical properties

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

• Steel’s high ductility means steel can be formed into useful shapes by pounding, rolling, and bending.

12.3 The arrangement of atoms and molecules in solids

• If the atoms are in an orderly, repeating pattern, the solid is crystalline.

• Examples of crystalline solids include salts, minerals, and metals.

12.3 Amorphous solids

• Rubber, wax and glass are examples of amorphous solids.

• The word amorphous comes from the Greek for “without shape.”

• Unlike crystalline solids, amorphous solids do not have a repeating pattern of molecules or atoms.

• Plastics are useful and important amorphous solids.

Chemistry Connection

• He named the compound “Silly Putty” after the main ingredient, silicone.

• Scientists who study how matter have another term for Silly Putty: it’s a viscoelastic liquid.

Silly Putty

In 1943, James Wright, a researcher for General Electric, dropped some boric acid into silicone oil, creating a gooey compound.

Activity

• The exact recipe for Silly Putty is kept secret, but you can make your own viscoelastic liquid with ingredients you may have around the house.

Make your own viscoelastic liquid