Hot & Cold

LESSON 1

Before we begin…

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The Particle Theory of Matter States…

• All matter is made of tiny particles. Each substance has its own unique particles.

Substance A

Substance B

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The Particle Theory of Matter States…

• There are empty spaces between the particles that are very large compared to the particles themselves.

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The Particle Theory of Matter States…

• Particles are held together by very strong electric forces.

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The Particle Theory of Matter States…

• Particles are always in motion. When they are heated, they move faster and spread farther apart.

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Adding Thermal Energy

The particles in a solid block of ice are vibrating slowly

When heat is added, the particles start to move faster

Eventually, the particles move fast enough that they are not held in a rigid arrangement and can slide past each other

• This is a change of state (melting)

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Removing Thermal Energy

• The particles in gaseous water vapour are moving very quickly
• When heat is removed by cooling the gas, the particles start to move slower
• Eventually, the particles move slowly enough to change state and condense into liquid water

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Removing Thermal Energy

• When warmer objects come into contact with cooler objects, the faster moving particles of the warm objects bump into the slower moving particles of the cool object
• Some of the energy from the warmer object is transferred to the cooler object
• The faster moving, warmer object loses some energy
• the particles move slower and the object cools
• The slower moving, cooler object gains some energy
• the particles move faster and the object warms

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Hot Particles Meeting Cool Particles

• After we pour the tea in, the cup becomes very hot – The slower moving particles of the cup begin to move faster and warm
• The tea cools as it touches the cooler cup and air – The faster moving particles of the tea begin to move slower and cool

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• Before we pour the tea in the cup, the cup is at room temperature and is comfortable to touch

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Kinetic Energy

• Kinetic energy is the energy that all moving objects possess
• The faster an object is moving, the more kinetic energy it has

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Heat VS Temperature

• Heat is the transfer of energy from warm things to cool things

• a measure of the average kinetic energy of the particles of a substance

TEMPERATURE

HEAT

we measure the kinetic energy of the particles when we measure the temperature

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when we heat a substance, we add energy to it

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Thermal EXPANSION

• When substances are heated, their volume increases
• The increased energy speeds up the particles of the substance
• The particles move faster and greater distances, so they take up more space

Thermal expansion tanks are put on hot water heaters to avoid spillage and high water pressure in pipes

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Thermal CONTRACTION

• When substances are cooled, their volume decreases
• The decreased energy slows down the particles of the substance
• The particles move slower and smaller distances, so they take up less space

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Air in basketballs and tires on a cold day. When the air cools it takes up less space and the ball becomes flat

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Thermal Contraction and Expansion

EXPLAIN THIS…

SUMMER

WINTER

Power lines and telephone wires are longer on a hot day because of thermal expansion

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Thermal Contraction and Expansion

Power lines and telephone wires are longer on a hot day because of thermal expansion

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