Fluids and Forces FYI

Transcription

1 Objectives Fluids and Forces Describe how fluids exert pressure. Analyze how atmospheric pressure varies with depth. Explain how depth and density affect water pressure. Give examples of fluids flowing from high to low pressure. Fluid any substance that can flow Liquids and gases Pressure - force exerted over a given area Pressure = Force / Area Pascal (Pa)=1N/m 2 Fluids Exert Pressure, continued In the image below, the force of the air particles hitting the inner surface of the tire creates pressure, which keeps the tire inflated. The SI unit for pressure is the pascal. One pascal (1 Pa) is the force of one newton exerted over an area of one square meter (1 N/m 2 ). Pressure Click below to watch the Visual Concept. Visual Concept Pascal s Principle Pascal s Principle a change in pressure in an enclosed fluid will be transmitted equally. You may stop the video at any time by pressing the Esc key.

2 Pascal s Principle, continued Because of Pascal s principle, the touch of a foot can stop tons of moving metal. Create a Cartesian diver Write 2 paragraphs 1 st - describe what happens in detail 2 nd Explain why things happened Fluids move from areas of higher pressure to areas of lower pressure. Complete the Fluid w.s. Atmospheric Pressure The atmosphere is the thin layer of nitrogen, oxygen, and other gases that surrounds Earth. Atmospheric pressure is the pressure caused by the weight of the atmosphere. Atmospheric pressure is exerted on everything on Earth, including you. Atmospheric Pressure, continued The air inside this balloon exerts pressure that keeps the balloon inflated against atmospheric pressure.

3 Copyright by Holt, Rinehart and Winston. All rights reserved. Atmospheric Pressure, continued Pressure Changes and Your Body You may have experienced this adjustment is your ears have popped when you were in a plane taking off or in a car traveling down a steep mountain road. Chapter menu Resources Objectives Explain the relationship between fluid pressure and buoyant force. Predict whether an object will float or sink in a fluid. Analyze the role of density in an object s ability to float. Explain how the overall density of an object can be changed. Buoyant Force and Fluid Pressure Buoyant force is the upward force that keeps an object immersed in or floating on a liquid. Archimedes principle the buoyant force is equal to the weight of the fluid that the object takes the place of, or displaces.

4 Buoyant Force and Fluid Pressure, continued Why do you float easier in salt water than in fresh water? There is more pressure at the bottom of an object because pressure increases with depth. This results in an upward buoyant force on the object. Weight Versus Buoyant Force Sinking An object will sink if its weight is greater than the buoyant force. Weight Versus Buoyant Force, continued Will an object sink or float? That depends on the whether the buoyant force is less than or equal to the object s weight. Floating An object will float when the buoyant force on the object is equal to the object s weight. Buoyant Force on Floating Objects Click below to watch the Visual Concept. Visual Concept You may stop the video at any time by pressing the Esc key. Floating, Sinking, and Density More Dense Than Air Ice floats on water because it is less dense than water. Ice, like most substances, is more dense than air. So, ice does not float in air. Less Dense Than Air One substance that is less dense than air is helium gas. A given volume of helium displaces an equal volume of air that is much heavier than itself. So, helium floats in air.

5 Changing shape Changing Mass Changing Overall Density, continued Changing Volume Like a submarine, some fish adjust their overall density to stay at a certain depth in the water. Most bony fishes have an organ called a swim bladder which helps them change volume. Swim Bladder Objectives Click below to watch the Visual Concept. Visual Concept You may stop the video at any time by pressing the Esc key. Describe the relationship between pressure and fluid speed. Analyze the roles of lift, thrust, and wing size in flight. Explain Pascal s principle. Describe drag, and explain how it affects lift.

6 Fluid Speed and Pressure Bernoulli s principle as the speed of a moving fluid increases, the fluid s pressure decreases. Why does the shower curtain get sucked into towards you when you are taking a shower? Factors That Affect Flight, continued Bernoulli and Baseball The next slide shows how a baseball pitcher can take advantage of Bernoulli s principle to throw a curveball.