1. Forces in Fluids
Pressure

2. 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

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

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

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

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

7. 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

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

9. 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

10. 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

11. 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

12. Variations in fluid pressure
Atmospheric pressure and elevation
At higher elevations
There is _______ air above you
There is _______ air pressure
less
less

13. 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

14. Variations in fluid pressure
Atmospheric pressure and elevation
At lower elevations
There is more air above you
There is more air pressure

15. 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

16. 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

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

18. 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

19. 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.

20. 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

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