FORCES IN FLUIDS PRESSURE WHAT IS PRESSURE Pressure

FORCES IN FLUIDS PRESSURE

WHAT IS PRESSURE? • Pressure = a _____ force spread across the ____ of a surface area • Example • Your feet press on the floor • This force spreads out over the area of your feet

WHAT IS PRESSURE? • Pressure and area • Pressure _______ as decreases the area its spread across _______ increases • Larger area = _______ pressure less • Smaller area = ____ pressure more

WHAT IS PRESSURE? • Calculating pressure Force • Pressure = ______ / _______ Area • Units for pressure = _______ (Pa) Pascal • Units force = Newton (N) • Units for Area = square meters (m 2)

WHAT IS PRESSURE? • How pressure changes • If force increases, pressure _______ increases • If area increases, pressure decreases ________

FLUID PRESSURE fluid • A _____ is a material that can easily flow (liquids and gases) • Fluids take the shape of their containers

FLUID PRESSURE • What causes fluid pressure collide • Fluid particles ______ with each other and with the walls of their containers • When particles collide, they exert _______ forces air

FLUID PRESSURE • All of the particle forces combine to make the total force exerted by the fluid Total • Fluid pressure = ______ fluid force / area

FLUID PRESSURE • Air pressure • Surrounding the Earth is ______ 100 kilometers of a fluid called ______ air • Gravity pulls on air, causing the air to have _______ weight • This weight force presses down on everything on Earth’s surface, including you • This force is called ________ pressure atmospheric

FLUID PRESSURE • Balanced pressure • If you hold out your hand, you are holding 1, 000 N of air but you don’t feel it • In a fluid, pressure is exerted _______ in all directions equally • The fluid pressures _______ balance each other • Your hand does not feel the tremendous weight of the air

FLUID PRESSURE • Similarly, the air does not crush your entire body • The air outside pushes against your body • The fluids inside your body push back equally • The pressures balance and cancel and you are not crushed • If fluid pressures become unbalanced, objects can blow up or get crushed

VARIATIONS IN FLUID PRESSURE • Atmospheric pressure and elevation • At higher elevations less • There is _______ air above you • There is _______ less air pressure

VARIATIONS IN FLUID PRESSURE • Ear popping on an airplane • As the plane rises, the pressure inside you becomes greater than the pressure outside • To balance this, the body releases some of the air pressure inside you • This makes the popping noise/feeling

VARIATIONS IN FLUID PRESSURE • Atmospheric pressure and elevation • At lower elevations • There is more air above you • There is more air pressure

VARIATIONS IN FLUID PRESSURE • Water pressure and depth • At shallow depths • There is less water above • you There is less water pressure • At deep depths • • • There is _______ more water above you more water There is _______ pressure Effects: your sinuses start to hurt and it becomes harder to breathe

VARIATIONS IN FLUID PRESSURE • Measuring pressure • To measure pressure, we use a barometer ________ • An ________ barometer is useful aneroid for everyday, simple readings • Weather forecasters use it to determine if a storm is coming • Usually reports pressure in millimeters, inches or _______ millibars

REVIEW 1. What two factors does pressure depend on? Force and area

REVIEW 2. Who exerts more pressure on the ground – a 50 kg woman standing on high heels, or a 50 -kg woman standing in work boots? Woman in high heels because the force is exerted over a smaller area

REVIEW 3. Since most of the weight of the atmosphere is above you, why aren’t you crushed by it? The pressure that Earth’s atmosphere exerts on the body is equal in all directions.

REVIEW 4. Compare the change in atmospheric pressure with elevation to the change in water pressure with depth. Atmospheric pressure decreases with elevation, but water pressure increases with depth

REVIEW 5. Why must an astronaut wear a pressurized suit in space It balances the pressure outside and with the astronaut’s body.