Matter

2. Matter

3. Chapter Twelve: The Physical Properties of Matter • 12.1 Density • 12.2 Buoyancy • 12.3 Properties of Materials

4. 12.3 Pressure • A fluidis a form of matter that flows when any force is applied, no matter how small. • Liquids are one kind of fluid, gases are another.

5. 12.3 Pressure • A force applied to a fluid creates pressure. • Pressure acts in all directions, not just the direction of the applied force.

6. 12.3 Pressure • Forces in fluids are more complicated than forces in solids because fluids can change shape.

7. 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).

8. 12.3 Pressure • The pressure inside your tire is what holds your car up. Which units are normally seen on car tires?

9. 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.

10. 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.

11. 12.3 Energy conservation and Bernoulli’s Principle • Streamlinesare 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. 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.

13. 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.

14. 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.

15. 12.3 Mechanical properties • When you apply a force to an object, the object may change its size, shape, or both.

16. 12.3 Mechanical properties • “Strength” describes the ability of a solid object to maintain its shape even when force is applied.

17. 12.3 Mechanical properties • Elasticitydescribes a solid’s ability to be stretched and then return to its original size. • Brittlenessis defined as the tendency of a solid to crack or break before stretching very much.

18. 12.3 Mechanical properties • A ductile material can be bent a relatively large amount without breaking. • Steel’s high ductilitymeans steel can be formed into useful shapes by pounding, rolling, and bending.

19. 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.

20. 12.3 Amorphous solids • Rubber, wax and glass are examples of amorphoussolids. • 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.

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

22. 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.