Unit 3: Forces, Fluids and Density

Big Ideas of the Unit
All fluids demonstrate the property of viscosity, or
the internal friction that causes a fluid to resist
2. Density is an important property of fluids
3. Fluids exert a buoyant force on objects that causes
objects to float
4. Understand the properties of fluids that helps in the
design and construction of useful devices
What is a Fluid?
 Fluids include liquids AND gases
 They are substances that are able to flow and take shape
of a container
 Make oobleck using 1 part water : 1.5-2 parts cornstarch
(ie if you use two tablespoons of cornstarch, you will
need about one tablespoon of water)
 What are the characteristics that make it a fluid?
 What are the characteristics that make it a solid?
1.1 Investigating Viscosity
 Particle theory of matter:
 Solid matter have particles that are close together and in
a ‘fixed’ position
 Liquid matter have particles that are still close together
but the particles can ‘slide’ around
 Gaseous matter have particles that are far apart and
move quickly
 Can we make a new definition that included the
particle theory?
 Points to consider
Fluids can be poured
Fluids take the shape of the container
How can we add in the particle theory?
 Most fluids are safe and we interact with them
 However some fluids can be dangerous and they are
labeled using the WHMIS system (Workplace
Hazardous Material Information System)
 Fill in the WHMIS symbols
 One property of fluids is how they flow
 How fluids flow is determined by its viscosity
 Viscosity is how easily a liquid flows
 High viscosity= doesn’t flow well (ketchup)
 Low viscosity= does flow well (apple juice)
 Viscosity can be determined using the bubble test or
the ramp test (pour down a ramp and see which fluid
is the fastest)
 Bubble test- test various liquids to see which has the
most viscosity
 Higher viscosity= longer time for the bubbles to rise up
 Wrap-up discussion
As a group discuss the results and answer the questions
Viscosity is Important
 What causes viscosity?
 Particles are attracted to each other and this attraction
will determine how easily the particles ‘slide’ around
A strong attraction means the particles can not move as much
(think about a solid, the particles have a strong attraction to
each other)
Demo- jar of marbles vs a jar of yarn. The yarn is attracted to
the other yarn and do not move much as a result
 Write out a paragraph describing viscosity- use the
words: fluid, particles, flow and viscosity in your