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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