L1 - Moving Particles

objectives

Solids, Liquids and Gases

• Every material is a solid, a liquid, or a gas.
• Scientists have developed a model (description) called the kinetic theory to explain, how solids, liquids, and gases behave.
• According to this theory, matter is made up of tiny particles which are constantly in motion.
• The particles attract each other strongly when close, but the attractions weaken if they move further apart.

Solids

Gas

Liquid

a video on solids, liquids and gases

What are the Particles?

• Everything is made from about 100 simple substances called elements.
• An atom is the smallest possible amount of an element.
• In some materials, the 'moving particles' of the kinetic theory are atoms.
• However, in most materials, they are groups of atoms called molecules.
• Below, each atom is shown as a coloured sphere.
• This is a simplified model (description) of an atom.
• Atoms have no colour or precise shape.

Brownian Motion

• The kinetic theory' explains Brownian motion as follows.
• The bits of smoke are just big enough to be seen, but have so little mass that they are jostled about as thousands of particles (gas molecules) in the surrounding air bump into them at random.

Energy of Particles

• The particles (atoms or molecules) in solids, liquids, and gases have kinetic energy because they are moving.
• They also have potential energy because their motion keeps them separated and opposes the bonds trying to pull them together.
• The particles in gases have the most potential energy because they are furthest apart.
• The total kinetic and potential energies of all the atoms or molecules in a material is called its internal energy.
• The hotter a material is, the faster its particles move, and the more internal energy it has.
• If a hot material is in contact with a cold one, the hot one cools down and it loses internal energy, while the cold one heats up and gains internal energy.
• The energy transferred is known as heat.
• The term thermal energy is often used for both internal energy and heat.

A video on internal energy