Pressure and Fluids
Pages 66 – 84 in textbook.
What is a fluid?
 A substance that has the capacity to flow and assume
the form of the container into which it has been
poured.
What are some examples of fluids?
 Water, milk, blood and saliva
 Gases are also considered fluids: air, helium and
ozone.
The Particle Model.
 Used to explain how fluids change shape.
 Arrangement Of Molecules In The Three States Of
Matter – YouTube
 Solids, Liquids and Gases - YouTube
Odd Fluids
 Is toothpaste considered a fluid? What about sand?
Non-newtonian fluids.
 Non-Newtonian Fluid on a Speaker Cone - YouTube
There are two types of fluids:
 1) Compressible fluids: A fluid whose volume can
change. GASES.
 2) Incompressible fluids: A fluid whose volume cannot
be varied. LIQUIDS.
 Why are they different? Because the particles behave
differently under pressure.
Pressure
 The result of a FORCE applied in a PERPENDICULAR
fashion to a surface.
What is a force?
 A force is either a PUSH or PULL that changes the
movement or shape of an object.
 Effect of force on pressure:
 Force increases = Pressure increases
 Force decreases = Pressure decreases
Surface area and Pressure
 If surface area increases = Pressure decreases
 If surface area decreases = Pressure increases
How to we calculate pressure?




Pressure is equal to the force divided by the area.
Pressure is measured in Pascals (Pa)
Force is measured in Newtons (N)
Area is measured in square meters (m²)
𝐹
𝑃=
𝐴
Bill Nye: The Science Guy Pressure - YouTube
Bed of Nails - Cool Science
Experiment - YouTube
Pressure and Fluids, Part 2.
 Pressure exerted by fluids:
 When the fluid is incompressible, the force exerted
comes from the mass of the fluid above the object.
How density affects pressure.
 Density is a measure of much matter is “packed
together” in a solid/liguid/gas.
 The GREATER the density, the GREATER the pressure.
 SUMMARY: The pressure exerted on an object by an
incompressible fluid depends on –
1. The DEPTH of the object in the fluid.
2. The DENSITY of the fluid.
 Liquid Pressure - YouTube
Pressure exerted by a compressible
fluid
 The PRESSURE depends on:
1) The number of particle collisions, with each other or
with the sides of the container.
Factors that affect the number of collisions:
a) Number of particles
b) Temperature – higher temperature, more collisions
c) Volume of fluid
 Gas volume and pressure - YouTube
Pressure and the volume of a
compressible fluid.
 Volume increases – Pressure decreases
 Volume decreases – Pressure increases
 Pressure-Volume Relation ( Kinetic Molecular Theory )
- YouTube
Atmospheric Pressure
 The atmosphere is the layer of air that surrounds the
earth. This air is a mixture of gases, and it exerts
pressure on everything on the surface.
 We measure atmospheric pressure by using a
barometer.
 QUESTION: What happens to a barometer the higher
one goes in the atmosphere?
Pressure and the Human body.
 Real World: Heart Rate and Blood Pressure - YouTube