Forces in Fluids Pressure

What is pressure? Pressure = a _________ spread across the ________ of a surface Example Your feet press on the floor This force spreads out over the area of your feet force area

What is pressure? Pressure and area Pressure _____________ as the area its spread across ______________ Larger area = _______ pressure Smaller area = ________ pressure decreases increases less more

What is pressure? Calculating pressure Units for pressure = ______________ (Pa) Units for force = Newton (N) Units for Area = square meters (m2) Force Area Pascal

What is pressure? How pressure changes If force increases, pressure ______________ If area increases, pressure _______________ increases decreases

Fluid pressure A __________ is a material that can easily flow (liquids and gases) Fluids take the shape of their containers fluid

Fluid pressure What causes fluid pressure Fluid particles ___________ with each other and with the walls of their containers When particles collide, they exert _____________ collide forces air

Fluid pressure All of the particle forces combine to make the total force exerted by the fluid Fluid pressure = ___________ fluid force / area Total

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

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

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 There is _______ air above you There is _______ air pressure less less

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 _______ water above you There is _______ water pressure Effects: your sinuses start to hurt and it becomes harder to breathe more more

Variations in fluid pressure Measuring pressure To measure pressure, we use a ________________ An _______________ barometer is useful for everyday, simple readings Weather forecasters use it to determine if a storm is coming Usually reports pressure in millimeters, inches or ______________ barometer aneroid millibars

Review What two factors does pressure depend on? Force and area

Review Who exerts more pressure on the ground – a 50kg 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 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 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 Why must an astronaut wear a pressurized suit in space It balances the pressure outside and with the astronaut’s body.