1) Why is a solid not considered a fluid?

1) Why is a solid not considered a fluid?
• All fluids have the capacity to flow. Solids do
not have this characteristic, therefore they are
not fluids.
– Ex: flour does not flow when poured, instead it
forms a heap
– Ex: Sand does not flow when poured, it forms a
2) Do all fluids flow equally easily?
• All fluids do not flow equally easily as they
each have a characteristic viscosity which
affects their ability to flow.
– Ex: due to the nature of it’s particles, molasses is
very viscous and therefore does not flow as easily
as water
3) What is viscosity?
• Viscosity is a measure of a liquid’s resistance
to flow, in other words it’s ‘thickness’.
4) Why is viscosity an important
• Viscosity is an important characteristic for
engineers to consider when they are designing
machinery or distribution systems.
– Ex: it is important to consider a liquid’s viscosity
when designing a pipeline for it’s transport
– Ex: industrial lubricants must be designed with a
specific viscosity so the fluid may protect
mechanical parts from the effects of friction
5) What does the particle theory of
matter state?
• All matter is made up of tiny particles.
• These particles are constantly moving.
6) How are the position of the particles in solids,
liquids and gases different?
• Solids: particles are held in fixed positions so
that they move together.
• Liquids: particles are packed closely; however,
they have freedom of movement so that they
may move independently from one another
• Gases: particles are spaced far apart so that
they may move freely past one another.
Particles of a solid, liquid and gas
7) Using particle theory, explain why liquids
and gases can flow and solids can’t.
• Solids cannot flow because their particles are
held so tightly together that they cannot move
freely past one another (cannot flow)
• The particles are liquids and gases can move
independently and therefore may move past
one another, or flow.
8) What is pressure? Explain and give
the formula used to calculate pressure.
Pressure is the measurement of force exerted
on a surface (area)
P = Pressure in N/m2
F = Force in N (Newtons)
A = Area in m2
9) What 2 factors does the amount of
pressure depend on?
• Pressure depends on:
– the size of the force
– The total area on which the force acts
10) What happens to the pressure
when force is increased?
Pressure and Applied Force
• Pressure varies in direct proportion to the force
• When the size of the surface area is the same:
– The stronger the force the greater the pressure
– The weaker the force the lower the pressure
• Example:
– The force exerted by water increases as you dive deep
down, this causes the pressure to increase which changes
the shape of your eardrums causing a painful sensation
11) What happens to pressure when
surface area is increased?
Pressure and Surface Area
• Pressure is inversely proportional to the surface area upon
which force is applied
• With a constant force:
– The larger the surface area, the smaller the pressure
– The smaller the surface area, the greater the pressure
• Example:
– This is why standing on a single nail would pierce through your
foot whereas lying on a bed of nails would support your body
12) Why can a person walk on snow with
snow shoes but not with regular shoes?
• A person can walk on snow with snow shoes
but not with regular shoes because snow
shoes increase the surface area on which the
force (person’s weight) is acting, thus
decreasing the total amount of pressure.
13) What can one do to increase
pressure without changing the force?
• Decrease surface area.
14) What does ‘incompressible’ mean?
• Incompressible means that the volume
doesn’t change when pressure is applied.
15) What does ‘compressible’ mean?
• Compressible means that when pressure is
exerted, the fluid will shrink, or it’s volume will
16) Why are gases compressible when
liquids and solids are not?
• Gases are compressible because in their
natural state, their particles have enough
space between them that they may be
brought closer together when pressure is
• Liquids and solids are incompressible because
their particles are already so close together
that they may not be brought any closer, even
with a large amount of pressure.
17) Give an example of how
compressed air is used.
• Compressed air is used in submarines.
18) What is the standard SI unit
measurement for pressure?
Units of Pressure
• Pa (pascal)- this is the unit used in the international
metric system (SI)
• 1 Pa = 1N/m2
• 1 000 Pa = 1k Pa (kilopascal)
There are also 2 other types of units used:
• Mm of Hg (millimeters of mercury)
• Atm (atmosphere)
19) Why does pressure increase as a person
goes further and further underwater?
• This is because there is a greater force of
gravity pulling on the fluid as you go further
and further down.
20) Would the pressure be greater
under fresh water or sea water? Why?
• This is because pressure is also affected by the
density of the fluid. The greater the density of
the fluid, the more pressure would be exerted.
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