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

Make your own viscoelastic liquid Activity Make your own viscoelastic liquid 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.