Chapter 9 FluidsAcademic and Conceptual PhysicsSpring 2014

Nature of Matter All substances are

composed of atoms.

Atoms are mostly empty space.

The mass of the atom is concentrated in the nucleus.

Properties of Fluids

Fluids are materials that can flow – they have no definite shape – Liquids and Gases

Density is the mass to volume ratio of a fluid.

ρ = m/V where ρ is density, m is mass and V is volume. Units of ρ are kg/m3

Fluid Density

Solids and Liquids are generally incompressible.

Their densities are nearly constant

regardless of pressure.

Fluid Density

Gases are compressible and their densities vary with pressure.

Boyle’s Law Lab

Fluid Temperature

Kinetic theory predicts that temperature is proportional to the average kinetic energy of particles in a gas.

Increasing the temperature of a fluid increases the speed of particles.

The Ideal Gas The Ideal Gas Law relates the macroscopic

properties of Pressure, Temperature and Volume.

If the number of particles of gas are constant,

P1V1/T1 = P2V2/T2

where P is pressure, V is volume and T is temperature in Kelvin. (K = C + 273)

Archimedes’ Principle

Any object completely or partially submerged in a fluid experiences an upward buoyant force (FΒ) equal in magnitude to the weight of the fluid displaced by the object.

For a submerged object, FΒ < Fg

For a floating object, FΒ = Fg

Buoyant Force

The apparent weight of the object depends on the objects density.

Fg (object)/FB = ρ0/ρf

where the FB is theweight of the displacedfluid. (Archimedes Lab)

Pascal’s Principle

Pressure applied to a fluid in a closed container is transmitted equally to every point of the fluid and to the walls of the container.

F1/A1=F2/A2 where F is Force in N and A is the area in m2.

Pascal’s Principle

Fluid Pressure and Depth The fluid pressure

increases with depth.

P = Po+ ρgh Where P is the absolute pressure and p0 is atmospheric pressure.

Fluids in Motion

The Continuity Equation A1v1 = A2v2 where A is the area and

v is the speed. Water pressure on the right is less

than on the left.

Bernoulli’s Principle

The pressure in a fluid decreases as the fluid’s velocity increases.

Bernoulli’s Principle

ISS Demonstrations