Temperature Thermal Energy, and Heat The Kinetic Molecular Theory (KMT) explains that all matter is made up of tiny particles.  These atoms and molecules are constantly in motion.  KE is energy due to motion.

KMT All matter is made up of very small particles. These particles are in constant motion, which means they have kinetic energy. There are empty spaces between the particles. The particles and spaces are so small that they cannot be seen. If heat is added to a substance, its particles gain kinetic energy and move faster as a result.

Temperature Thermal Energy, and Heat

Temperature, Thermal Energy and Heat Temperature is the average KE of the particles of a substance.  The movement of particles is what we measure as temperature.  measured in degrees Fahrenheit (°F), degrees Celsius (°F), or Kelvin (K).

Temperature Since temperature is a way of measuring the average energy of the particles in an object, it does not change when the size of the object changes.

Temperature, Thermal Energy and Heat Thermal energy is the total energy of all of the particles in a substance.  Thermal energy = all KE + all PE  Recall: KE is the energy of movement.  PE is the energy of position (stored energy)  related to how much the particles vibrate, and how much space they take up.

Thermal Energy The amount of thermal energy depends on the size of the object - the larger the object, the more moving particles it contains.

Where is PE the greatest? Where is KE the greatest? PE (gravitational) is greatest here KE (mechanical) is greatest here

Measuring Energy SI units = Joules (J) often use kJ or MJ, since 1 J is a very small amount of energy

Temperature, Thermal Energy and Heat

Heat is the amount of thermal energy transferred from an object at a higher temperature to an object at a lower temperature. Ex. When you cup your cold hands around a mug of hot chocolate, heat is transferred from the mug to your hands.

Heat Transfer Energy transfers from particles of greater average energy to particles of lower average energy. This process is called heat transfer. 3 methods of heat transfer: Conduction Convection Radiation

Thermal Energy Transfer – Conduction Conduction is the transfer of thermal energy by direct contact.  Heat is transferred from high temperature, high KE particles to lower temperature, lower KE particles.  Ex. a cold spoon warms up when placed in a cup of hot coffee  Thermal conductors (ie. copper) transfer heat easily, while insulators (ie. styrofoam) do not.

Thermal Energy Transfer – Convection Convection is the transfer of heat energy in fluids (liquids and gases).  Convection is the movement of heat energy from hot to cold areas within a fluid, or the movement of hot liquid to an area of cool liquid.  Because there is a density difference, warm fluid (low density) moves to cold.  This is how convection currents form!

Convection Currents - Heating a pot of soup… Soup particles on the bottom of the pot (near the heat source) gain speed and move farther apart as they’re heated. This (warmer) part of the soup is less dense than the cooler parts of the soup, therefore rises and the cooler, denser soup sinks. Convection currents in liquids and gases are similar.

Thermal Energy Transfer – Radiation Heat transfer by conduction and convection depends on the motion of particles. Radiation does not require particles to transfer energy. Radiation is the transfer of radiant energy by waves.  What we feel as heat is generally called infrared radiation.  Earth’s interior thermal energy comes from the core, plus from the decay of some radioactive elements.

Radiation Ex. Light and heat come to us from the sun as radiant energy. (The space between the Earth and the Sun contains almost no particles.)

Properties of Radiant Energy Light energy and radiant heat can both travel where there are few particles of matter. …both travel at the speed of light (c). …both travel only in straight lines. Radiant energy can be reflected or absorbed by objects, and can also be transmitted (ie. pass through materials such as glass).

Solar Radiation