Unit 3 – Forces in Fluids Chapters 3 and 13 Read Pages 69 - 73

A fluid is a substance that assumes the shape of its container Fluids can be a liquid or a gas

Kinetic Theory of Matter Says all particles of matter are in constant motion! Kinetic comes from the Greek word meaning “to move” Kinetic energy is the energy of motion This theory helps explain the behavior of liquids and gases

Liquids There are forces of attraction among the particles of matter This attraction keeps the particles close together Atoms touch but slide past one another

Liquids (continued) Definite (fixed) volume – it cannot be compressed Indefinite shape – it takes the shape of the container

The fast moving atoms are spread out and only touch when they collide Gases The fast moving atoms are spread out and only touch when they collide Particles are apart and moving so fast the attractive forces are too weak to have an effect

Gases (continued) Has an indefinite shape – They will fill the container Indefinite volume – They can be compressed

Pressure is the amount of force distributed over an area Force (Newtons) Pressure Area (Square meters – m2)

The SI unit of pressure is a Pascal (Pa) Newtons per square meter (N/m2) is known as a Pascal This unit is often changed to kilopascals (kPa)

Practice A box with a weight of 2700 Newtons is resting on the ground. If the area of the box touching the ground is 1.5 square meters, then what pressure does the box exert on the ground? Force 2700 N Pressure 1800 N/m2 Area 1.5 m2 1800 N/m2 1800 Pa or 1.8 kPa

Pressure in Fluids Pressure in a non-moving fluid is determined by: Type of fluid (Density is different for each) Depth within the fluid Pressure increases as depth increases

Pressure in Fluids (continued) Pressure at any depth is constant and is exerted equally in all directions

Pressure in Fluids (continued) The amount of a fluid in regards to volume or weight does not affect pressure (Page 392 – Figure 3)

1 Pascal is not much pressure but even our atmosphere exerts pressure on us

Atmospheric pressure = about 101,300 pascals

Empty bottle sealed at 14,000 feet Same bottle at 9,000 feet Same bottle at 1,000 feet

The amount of available oxygen becomes less and less as you move to higher elevations

Certain types of weather are accompanied by pressure changes

Fluids will move from a high pressure to a lower pressure