Thermal Expansion

Magnitude of Expansion of Solids, Liquids and Gases

Examples of Expansion

Relationship between pressure and volume at a constant temperature

Thermal Expansion

• When molecules are heated they move far apart from each other– This causes the material to expand

• Expansion– Increase in size of a material due to

added heat • When molecules are cooled, the

molecules, move closer to each other– This causes the material to contract

• Contraction– Decrease in size of a material due to

heat removed

Let us look at 3 videos on the example of expansion and contraction

Applications of Thermal Expansion

Bimetallic strip as thermometer

Applications of Thermal Expansion

Liquid Expansion as thermometer

Road expansion gaps

Applications of Thermal Expansion

Tyre Fitting

Thermal Expansion

• All materials expand– Solids have linear expansion

• Varies among materials– Liquids and Gases have volume

expansion• Varies among materials

• Gases expands more readily than gas

• When a materials changes from solid to liquid, volume does not change much

• When a liquid changes to gas, the volume expansion is about 1000 times more

Pressure of a Gas

• Pressure of a gas– Force per unit area– Force is due to collisions with the walls of the

container– Units: Nm-2 or pascal, Pa

Pressure and Volume of a Gas at Constant Temperature

• At constant temperature, what happens to the volume of the gas when the pressure increases?

• At constant temperature, what happens to the pressure of the gas when the volume decreases?

• Boyle’s LawPα1/VpV = constantp1V1=p2V2