Starter 4/21/14

• 1. What is the difference between a solid, liquid, and gas?

• 2. How does a boat float?

Properties of Fluids

2/5/13

Fluids• Flow

• Have no definite shape

• Ex: gasses and liquids

Pressure• Applying force to a surface

• F is perpendicular to A• Unit of measure is pascal (Pa) = 1 Newton per

square meter. Since this is small, we usually see kilopascals (kPa).

P = FA

Pascal’s Principle• The shape of a container has

no effect on the pressure of the fluid it contains at any given depth.

• Any change in pressure applied at any point is transmitted throughout the fluid.

• Ex: squeezing a tube of toothpaste.

Hydraulic Lifts

Buoyant Force• The upward force on an object from the fluid. • If the buoyant force is greater than or equal to

the weight of the object, it will float.

Archimedes Principle• The magnitude of a buoyant force is equal to the

weight of fluid displaced.

• Fish and air bladders

Bernoulli’s Principle• As the velocity of a fluid increases, the pressure

exerted by the fluid decreaseshttp://www.youtube.com/watch?v=P-xNXrELCmU http://www.youtube.com/watch?v=WDGNcmEOjs4

Cohesive Forces• Forces of attraction that particles exert on each

other.

Surface Tension• Tendency of the surface of a liquid to contract to

the smallest possible area.• Top molecules are attracted to the sides and

downward, but not upward.

Adhesion• Attractive force between particles of different

substances.

Capillary Action• Water rises in a glass

tube because the adhesion between glass and water is stronger than the cohesive force of water.

• Water rising upward in soil to plant roots

Evaporation• Fast moving particles on the surface of a

liquid “escape.” – break free of cohesive force.

• Since kinetic energy is lost, evaporation has a cooling effect

• Liquids that evaporate quickly are called volatile liquids (rubbing alcohol)

• Humid days reduce evaporation of our perspiration, so we feel hotter.

Condensation• If the kinetic energy

decreases, particles turn back to a liquid.

• What is the Dew Point on the weather forecast?