THERMAL Energy Chapter 5

TEMPERATURE All matter is made of small particles which are in constant motion. Because the particles are moving, they have kinetic energy. The temperature of an object is the measure of the average kinetic energy of particles that make up that object. As the temperature increases, the average speed of the particles increases As the kinetic motion of the particles decreases, the temperature decreases.

Thermal energy Particles have potential energy that can be changed into kinetic energy; similar to ball where the higher up the ball is from Earth, the greater the GPE. For particles, the further apart they are, the greater the potential energy. As the particles move faster, the kinetic energy increases. Thermal energy is the sum of the kinetic energy and potential energy of all of the particles that make up an object. Example of thermal energy: when butter is pulled out of the fridge, it is cold and hard. The air temperature is warmer, so the particles are moving faster. The air particles and butter particles bump into each other, and kinetic energy is transferred from the air to the butter.

How are thermal energy and temperature related? When the temperature of an object ↑, the average kinetic energy ↑ When the average kinetic energy ↑, the object’s thermal energy ↑ Therefore, the thermal energy ↑ as the temperature ↑

heat Heat is thermal energy that flows from something at a higher temperature to something at a lower temperature Heat is a form or energy, so it has units of J Heat always flows from warmer materials to cooler materials In a glass with water and ice, water is actually transferring its thermal energy to the ice, warming the ice

Conduction Occurs when particles within a substance or between two substances bump into each other and transfer kinetic energy Conduction transfers thermal energy from warmer areas to cooler areas, without transferring matter Example: Spoon left in a pot of soup; eventually the handle gets hot from spread of thermal energy

convection The transfer of thermal energy in a fluid by the movement of warmer and cooler fluids from one place to another A fluid is a substance that can flow; can be a liquid or gas; the movement of fluids from one place to another causes currents which transfer thermal energy Example: Heating a pot of water: The water n the bottom gain thermal movement from the stovetop and rise to the top because they become less dense, and the cold water sink to the bottom because more dense. This rising and sinking creates a current, and continues until water heated.

How are conduction and convection different? Convection transfers thermal energy by moving particles from one place to another In conduction, thermal energy is transferred by particles bumping into surrounding particles. No particles move from place to place like convection.

radiation Transfer of energy by electromagnetic waves. The electromagnetic waves carry energy through solids, liquids, and gases, as well as through empty space. Also called radiant energy. Example: When you sit by a fire and feel warm from the heat transferred by radiation from the fire to your skin. Transfer of energy by radiation works best with gases

Thermal insulator Material in which heat flows slowly Examples: wood, air, some plastic

problems Why does the air temperature near the ceiling of a room tend to be warmer than the air temperature near the floor? Because of convection currents; warmer air is less dense, and cooler air is more dense, so the less dense (warm) air rises above the more dense (cooler) air

problems Which is temperature most directly related to? Kinetic energy Mechanical energy Potential energy Thermal energy a. Kinetic energy