2. Forces in Fluids PressureBouyancy Pascal’s Principle Bernoulli’s Principle

3. Pressure  Force that acts over a certain area  Pressure = Force ÷ Area  Force is measured in Newtons, area in cm 2, so pressure is N/ cm 2.  Or Pascals =N/m 2

4. Example problem 1  A woman weighs 750 N. She is standing on high heels with a total area of 2 cm 2 touching the ground. How much pressure does she exert?  750N ÷ 2 cm 2 = 375 N/cm 2

5. What puts a greater force on a bamboo floor? A two ton car? An African elephant? A 125 pound woman with high heels? Measured in pounds per square inch, (PSI), a car has a load of 28 to 30 PSI, an elephant 50 to 100 PSI, and a 125 pound woman with high heels, when she takes a step and those hit the floor, 2,000 PSI!

6.  A fluid is a substance that can easily change its shape, such as liquids and gases.  Fluids act in all directions. Fluid Pressure  Pascal’s Principle when a force is applied to a confined liquid the change in pressure is transmitted equally in directions

7. All the molecules add up together to make up the force exerted by the fluid.

8. Fluid pressure increases with depth.  Scuba divers feel an extra atmosphere of pressure every 33 feet (10 meters) they descend.

9. Water pressure increases with depth.

10. Why does pressure increase with depth?  As a diver descends, the particles of fluid above her push down because of gravity.  Gravity is a force that is acting on the fluid.  The water still pushes on her from all directions, but as she goes deeper, there is a greater column of water above her.

12. Density and buoyancy: An object that has a greater density than the fluid it is in, will sink. If its density is less than the fluid it will float.

13. 1g/cm³

15. Buoyant Force The upward force exerted by a fluid on a submerged or floating object.

16. Buoyancy  The buoyant force works opposite the weight of an object.

17.  A solid block of steel sinks in water. A steel ship with the same mass floats on the surface.

18. Archimedes Principle  There are 2 ways objects can float:  1) If the buoyant force on an object is equal to the weight of the fluid displaced by the object.  2) If the density of the object is less than the density of the liquid.  What is the density of water?  1 g/ml  Will gasoline, with a density of 0.7 g/ml float or sink in water?  It will float!

20. If the weight of the water displaced is less than the weight of the object, the object will sink Otherwise the object will float, with the weight of the water displaced equal to the weight of the object. Archimedes' Principle explains why steel ships float. Steel is more dense than water, so why do ships float?

22. Bernoulli’s principle-as the speed of a moving fluid increases, the pressure exerted by the fluid deceases. This is the reason planes fly.

23. There are 4 forces in flight  Thrust- jet engines and propellers create lift which moves the plane forward.  Drag- air friction which must be overcome for the plane to fly.  Weight- pulling the plane down.  Lift- raises the plane.

25. Bernoulli’s principle explains how lift is created.  Faster moving air has less pressure.  The shape of the wing makes the air move faster over the top, creating lift to make the plane rise.

26. Air moves faster over the top of the wing, creating less pressure.