1. Fluid Mechanics ICP Chapter 8

2. Liquids & Gases Have the ability to flow. Flow = the pieces can move around each other. Because they can flow, they are called fluids.

3. Density – a measure of compactness, or – how much mass occupies a given space, or – amount of matter per unit volume

4. Density (cont.) Units = g/cm 3 or kg/mL water = 1 g/cm 3 Mercury = 13.6 g/cm 3 Iridium = 22.6 g/cm 3 (densest substance on Earth)

5. Density Problem A block has a mass of 22 kg. Its volume is 2.6 cm 3. Calculate its density.

6. Concept Checks Which has greater density, 1 kg of water or 10 kg or water? Which has greater density, an entire candy bar or half a candy bar?

7. Densities: water = 1.0 g/cm 3 aluminum = 2.7 g/cm 3 ethanol = 0.81 g/cm 3 Looking at the densities above, what do you think will happen when aluminum is placed in water? – It sinks because it has a higher density What will happen when ethanol is placed in water? – It floats because it has a lower density What can you predict about the density of ice? – It must be less than water, and it is – 0.92g/cm 3

8. 8.2 Pressure in Fluids Pressureforcearea Pressure depends on force and area. more area less pressure If you spread the force over more area, there is less pressure.

9. 8.2 Pressure in Fluids Pressureforcearea Pressure depends on force and area. more area less pressure If you spread the force over more area, there is less pressure. The formula to calculate pressure is: Pressure = force area pascal The S.I. unit that we use for pressure is the pascal (Pa)

10. 20 N Push Which creates more pressure? 20 N Push 10 cm 5 cm

11. If this woman were to step on you, which part of the shoe creates more pressure? Force (weight) Area Same force over smaller area creates more pressure under the heel. Force (weight)

12. What causes fluid pressure? particles pushing against a surface Pressure in fluids is caused by the particles pushing against a surface. Each particle gives a teeny tiny push, but they all add up. more crowded harder they push The more crowded the particles are, the harder they push. fasterharder they push The faster they are moving, the harder they push.

13. Pressure in Liquids Swimming under water you can feel the water pressure. Pressure in water is due to the weight of the water directly above you. Pressure in liquids depends on depth, NOT on volume of liquid. You feel the same pressure 1m under the surface of a small pool as you would 1m under the surface of a lake.

14. less pressuremore pressure Is there less pressure or more pressure on top of the mountain? Why? Because air has weight, and if there is less air above you, then there will be less weight. The weight of the fluid causes the pressure! More Fluid Less Fluid Lower Pressure Higher Pressure

15. Plastic bottle sealed at 14,000 feet on Mauna Kea observatory on the island of Hawaii, taken down to 9000 feet and then 1000 where the air pressure is crushing the bottle.

16. Force in Force out Force in Force out You can’t feel the atmospheric pressure because your body fluids push back! The forces are balanced. If air has weight, why don’t we feel the atmospheric pressure?

17. pressure Is there more pressure on the divers or the shark? How do you know? Because water has weight, and if there is more water above you, then there will be more weight. The weight of the fluid causes the pressure! More Fluid Less Fluid

18. What part of an iceberg has the most pressure on it? Pressure increases as you get deeper! Remember that pressure pushes in all directions so the iceberg is being pushed on all sides, all the way around.

19. 8.3 Buoyancy in Liquids When an object is in a liquid, the liquid exerts an upward force on it. This upward force is called the buoyant force

20. If the weight of the submerged object is greater than the buoyant force, the object will sink. If the weight of the object is equal to the buoyant force, the object will remain at any level (like a fish). If the buoyant force is greater than the weight of the object, it will rise to surface and float.

21. Weight of the boat Buoyant Force Objects float when the forces are balanced! Objects sink when the forces are unbalanced! Weight of the coin Buoyant Force

22. Weight Buoyant Force Buoyant Force Weight When weight is equal to buoyant force, things float. When weight is more than buoyant force, things sink.

23. Objects float when the forces are balanced! Weight = Buoyant force Objects sink when the forces are unbalanced! Weight > Buoyant force weight buoyant force weight buoyant force How do you know if an object will float or sink?

24. Archimedes’ Principle Relationship between buoyancy and displaced liquid. “An immersed body is buoyed up by a force equal to the weight of the fluid it displaces. If an immersed body displaces 10 N of fluid, the buoyant force on it will be 10 N. http://www.youtube.com/watch?v=yB8c5t8Ct 7I&noredirect=1 http://www.youtube.com/watch?v=yB8c5t8Ct 7I&noredirect=1

25. Understanding buoyancy Displacement = pushed aside Volume of water displaced = the amount of water that is pushed aside when something enters the water. A completely submerged object always displaces a volume of liquid equal to its own volume.

26. Using displacement to determine the volume of an object

27. Sink or Float? If the weight of the volume of fluid pushed aside is greater than or equal to the weight of an object, the object will float.  Since the object sinks, the weight of the 2 units of liquid displaced must weigh less than the object.

28. An immersed body is buoyed up by a force equal to the weight of the fluid it displaces. The “apparent” weight of an object decreases when immersed in a fluid.

29. Floating A floating object displaces a weight of fluid equal to its own weight.

30. Every floating object (ship, submarine, blimp) must be designed to displace a weight of fluid equal to its own weight. A ship that weighs 10,000 tons must be designed to displace 10,000 tons of water. A blimp that weighs 100 tons must be designed to displace 100 tons of air. (if it displaces more it rises, less it descends)