Kinetic Particle Theory

Scientific model

- 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.