- What is a scientific model?
ü A
representation, a prototype or replica of the object/phenomenon that could well
explains its physical properties.
ü It can be
represented using animation or static diagrams.
ü Phenomenon
includes physical phenomenon like diffusion, dissolving, boiling, condensation,
evaporation, melting, sublimation etc.
ü Physical
properties include volume, density, conductivity etc…
- Types of Models
ü Physical
model
ü Scale
models
ü Computer
models
ü Mathematical
models
- Models are used to…
ü Make
predictions
ü Help in
investigations
ü Summarize
data
- Characteristics of Models
ü Models have
approximations to Nature
ü Models have
limitations eg, they do not represent nature in every aspect
ü Scientists
can use different models to describe the same thing (eg. Bohr’s model and
Schroedinger’s equation)
ü Models are
subject to revision and/or rejection when there’s new information.
- What are assumptions & limitations?
ü Assumptions
are valid statements to set the parameters for the model to work. Without the
assumptions, the principles of the model become invalid or irrelevant.
ü Limitations
are features of the model not aligned with the actual properties and go against
the principles of the phenomenon.
- Assumptions of the Kinetic Particle Model
ü Particles
are in constant motion and in random directions.
ü Particles
possess kinetic energy.
ü Forces of
attraction exist between particles.
ü Heavier
particles travel slower than lighter particles.
ü Particles
do not stick to each other after collision (elastic collision).
ü Particles
do not stick with the walls of container and bounces back after collision with
the walls of container.
ü Particles
travel in a straight line.
ü Particles
are small and discrete.
- Limitations
of the Kinetic Particle Model
ü Forces of
attraction between particles are not seen in the model. (Only for static
picture but can be shown clearly on animation)
ü Movement of
particles in terms of direction and speed may not be accurately captured on
static picture but can be shown clearly on animation.
ü Size of the
particles of an element may not be uniform. (Size of particles can be drawn
uniformly) NOT
LIMITATION
ü Distance
between particles in model may not be scaled accurately to the actual distance
between particles.
ü Size of the
particles in model may not be scaled accurately to the actual particles’ size.
(You can scale the particle’ size accurately in both static picture &
animation) NOT LIMITATION
Analogy to explain
Kinetic Particle Theory
- One example : A rock concert to
illustrate inter-conversion of solid (during concert) to liquid (when concert
ends) - (melting)
Features
similar to kinetic particle model
|
Assumptions
|
Limitations
|
ü During
concert, people are closely packed & jumping at fixed positions, just
like particles in solid state etc...
ü When
concert ends, people are moving disorderly sliding past each other but still
closely packed, just like particles in liquid state etc.
|
ü People
are in large in numbers yet small in size relative to entire concert hall.
ü People do
not stick to each other upon collision.
ü Each
person possesses kinetic energy.
ü Each
person moves in constant and random motion.
|
ü People
are of different sizes/masses unlike particles that are of same size/mass of
same substance.
ü There is
no force of attraction between people unlike particles that consist strong
forces of attraction between them.
ü People are
not standing in ordered arrangement, unlike particles in solid state in
ordered arrangement.
|
Physical
properties of 3 states
- A solid
ü
Cannot be compressed, thus a definite volume
ü
Has definite shape
ü
High density
ü
Force of attraction is the most
ü
Arrangement of particles are very packed and motion is
very little
- A liquid
ü
Cannot be easily compressed, thus a definite volume
ü
Has no definite shape – take the shape of the container
ü
High density (usually lower than solid)
ü
Force of attraction is less than solids
ü
The arrangement of the particles are slightly packed
and the motion is a little more than solids
- A gas
ü
Can be easily compressed, thus an indefinite volume
ü
Has no definite shape – take the shape of the container
ü
Low density
ü
Force of attraction is the least
ü
The arrangement of the particles are loosely-packed
and the motion is in constant random movement.
