11Temperature and Thermal EnergyTemperature and Thermal Energy

Temperature and energy

Glencoe: Chapter 9 – Section 1: pages 254-259

11

• The motion of the particles in matter is described by kinetic theory of matter.

• Matter is composed of particles that are atoms, molecules, or ions that always are in random motion.

Kinetic Theory of Matter

Temperature and Thermal EnergyTemperature and Thermal Energy

• The temperature of a substance is a measure of the average kinetic energy of its particles.

11

• The SI unit for temperature is the Kelvin (K).

• As kinetic energy increases the temperature increases

Temperature

Temperature and Thermal EnergyTemperature and Thermal Energy

11Temperature and Thermal EnergyTemperature and Thermal Energy

• Here is a picture showing the three temperature scales side by side

11 Temperature

Temperature and Thermal EnergyTemperature and Thermal Energy

• B. Thermometer – device that measures temperature

Relies on expansion of heated materials and

contraction of cooled materials

11 Temperature

Temperature and Thermal EnergyTemperature and Thermal Energy

1. Liquid thermometers – glass tube filled with a liquid

Limited temperature rangea. Mercury filledb. Alcohol filled

Particles move faster as heated and expand andrise up the tube

11 Temperature

Temperature and Thermal EnergyTemperature and Thermal Energy

2. Metal thermometers

2 bonded strips of metal (2 different metals) that expand and contract at different rates

A coiled piece of metal

11 Temperature

Temperature and Thermal EnergyTemperature and Thermal Energy

• Commonly used temperature scales are the Celsius (oC) scale, the Fahrenheit (oF) scale, and the Kelvin (K) scale.

11 Temperature

Temperature and Thermal EnergyTemperature and Thermal Energy

Energy Transfer (heat and temperature) - A sense of touch is very important for

determining temperature

- If the temperature of an object is lower than skin temperature = cold material (ice)

Energy is transferred from the warmer material (skin) to the cooler material as

the object’s particles collide with the skin particles

11 Temperature

Temperature and Thermal EnergyTemperature and Thermal Energy

• If the temperature of an object is higher than skin temperature = warm material (hot water bottle)

Energy is transferred from the warmer

material to the cooler material (skin) as

the object’s particles collide with the skin

particles

11

• The sum of the kinetic and potential energies of all the particles in an object is the thermal energy of the object.

• The increase in an object’s speed doesn’t affect the random motion of its particles, so it doesn’t affect its thermal energy.

Thermal Energy

Temperature and Thermal EnergyTemperature and Thermal Energy

11

• Heat is thermal energy that flows from something at a higher temperature to something at a lower temperature.

• Heat is a form of energy, so it is measured in joules.

• The flow of energy always flows from higher energy (hot) to lower energy

** Warmer will try to “heat up” the cooler**

Heat

Temperature and Thermal EnergyTemperature and Thermal Energy

33Ways to Transfer Thermal Energy

• Energy transfers from one object to another

• This transfer of energy as heat (thermal energy) as particles collide or objects collide is called conduction.

• Kinetic energy is transferred when these faster-moving atoms collide with slower-moving particles.

Transferring Thermal EnergyTransferring Thermal Energy

Conduction

33Convection

• Convection is the transfer of thermal energy in a fluid by the movement of fluid from place to place.

• Transfer of energy by the movement of fluids with different temperatures.

Transferring Thermal EnergyTransferring Thermal Energy

• A fluid expands as its temperature increases.

• The density of the fluid therefore decreases.

33Convection Current

• Flow of a fluid due to heating and cooling

• Warm fluids rise because they expand and become less dense (lighter), then cool.

Transferring Thermal EnergyTransferring Thermal Energy

• The warm water transfers thermal energy to the cooler water around it.

33Convection

Transferring Thermal EnergyTransferring Thermal Energy

• As the warm fluids cool, they contract and get heavier (denser) and sink.

• As fluids sink they are warmed up again by the heat source.

• The rising and sinking water forms a convection current.

33Radiation

• Radiation is the transfer of energy by electromagnetic waves.

Transferring Thermal EnergyTransferring Thermal Energy

• Radiation can pass through solids, liquids, and gases, but the transfer of energy by radiation is most important in gases.

• Examples: light, ultraviolet light, infrared

light, sunlight, microwaves, x-rays

• Does not involve the movement of matter.

33Radiation

Transferring Thermal EnergyTransferring Thermal Energy

• When radiation strikes

a material, some energy

is absorbed, some is

reflected, and some

may be transmitted

through the material.

33Transferring Thermal EnergyTransferring Thermal Energy

Conductors and Insulators1. Conductor – material through which energy

transfers easily

- Examples – metals (energy transfers between

particles easily)

solids (not all solids) tend to be better

conductors

gases tend to be poor conductors

Conductors and Insulators

2. Insulator – material that poorly transfers energy

- Examples – wood, plastic, rubberized materials, air, water