Chapter 7 Forces in Fluids Section 1 Fluids and Pressure

Essential Questions for 7-1 How do fluids exert pressure? How does atmospheric pressure vary with depth? How does depth and density affect water pressure?

Fluid Mechanics Liquids and gases have the ability to flow - they are called fluids There are a variety of “LAWS” that fluids obey

Pressure A measure of the amount of force exerted on a surface area The SI unit for pressure is the pascal. 1 pascal (Pa) is the force of one newton on an area of 1 m 2

Pressure and Bubbles An important property of fluids is that they exert pressure equally in all directions. Air blown into a bubble makes the bubble expand in all directions bubble

Atmospheric Pressure (Air) Atmospheric pressure is just the weight of all the air above an area pressing on the surface of the earthair Atmospheric pressure effects all objects Closer to sea level = more atm. pressure Higher up (mts.) = less atm. pressure

Discussion 1: Since atmospheric pressure is exerted everywhere on Earth including on the human body, why doesn’t this crushing pressure cause your body to collapse? Explain how this principle relates to why deep sea diving can be dangerous and why divers carry tanks of air under pressure.

Pressure in a Liquid (Water) Water pressure is just the weight of all the fluid above an object Are you stronger than water pressure?water pressure In a swimming pool the pressure on your body surface is just the weight of the water above you (plus the air pressure above the water)

Pressure in a Fluid So, fluid pressure is the gravitational force acting on the mass ABOVE you The deeper you go in water, the more weight above you and the more pressure

Discussion 2: Why does water pressure increase as the depth of the water increases?

Density Regardless of form (solid, liquid, gas) we can define how much mass is squeezed into a particular space

Discussion 3/Demo: You have been given two different fluids with unknown densities. How could you determine which fluid is denser without mixing the two fluids together?

Pressure in a Fluid Pressure acts perpendicular to the surface and increases at greater depth.

Pressure in a Fluid Deeper the hole is in the cup = More water pressure *This means water will spray out farther, the lower the hole is*

Pressure Differences and Fluid Flow (air or water)Flow Fluids flow from the areas of high pressure to areas of low pressure Straws work due to air pressure The air you inhale and exhale is also flowing from high pressure to low pressure Air pressure inside a tornado is very low, so air (and objects) outside the tornado are sucked inside

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Weather and pressure Barometric pressure is a measure of the force exerted on objects by the weight of the atmosphere above them.

Common highs and lows

7-1 Mini Quiz: 5 Questions 1.Which of the following statements about fluids is NOT true? a.All can flow. b.Some take the shape of their container. c.Liquids and gases are included. d.Particles move easily past each other.

2.When air is pumped into a tire, a.the force per unit area increases. b.the number of pascals decreases. c.the air particles slow down. d.the air takes up less space.

3.The nitrogen, oxygen, and other gases surrounding Earth a.exert pressure only at sea level. b.are pulled toward Earth by gravity. c.exert pressure that works against atmospheric pressure. d.are found mainly near the outer edge of the atmosphere.

4.Water pressure a.decreases with depth. b.is about twice as much on a diver at 10 m as at the surface. c.is less than air pressure for the same volume of air and water. d.is unaffected by atmospheric pressure.

5.Air rushes into your lungs when you inhale because a.it contains oxygen. b.the pressure inside the lungs is higher than outside the body. c.a muscle moves upward and decreases the space in your chest. d.fluids flow from areas of high pressure to areas of low pressure.