Unit 6 Thermal Energy 8th Grade Science: KMS

How is Thermal Energy Transferred? 3 ways Thermal Energy can transfer: Conduction Convection Radiation

Conduction Conduction – the transfer of thermal energy between materials by the collisions of particles. (there needs to be direct contact of particles) In what state of matter does conduction occur best in? Why? Solids because the particles that make up a solid are in direct contact.

Conductor vs. Insulator Conductor – material through which thermal energy flows easily. Conductors have a low specific heat Examples: iron, aluminum, silver (best), copper, lead, brass Insulator – a material through which thermal energy does not flow easily. Insulators have a high specific heat. Slows the transfer of heat. Examples: glass, wood, plastic, rubber, air, wool, cork, straw, paper.

Demonstrate your understanding On the back of the Conduction sheet draw and label an example of conduction.

Convection Convection – heat is transferred by the movement of currents within a fluid due to differences in density and temperature. Convection current – The movement of a fluid, caused by differences in temperature, that transfers heat from one part of the fluid to another This happens because hot molecules are less dense and rise whereas cold molecules are denser and sink

Density Heat transfer by convection is caused by differences of temperature and density within a fluid. Density = Mass/Volume

Convection heats our atmosphere

Convection currents also heat the Mantle

Demonstrate your understanding On the back of the Convection sheet draw and label an example of convection.

Radiation Radiation - The transfer of thermal energy from one material to another by electromagnetic waves. Radiation does NOT require matter to transfer thermal energy. All the Sun’s energy that reaches the earth travels though millions of kilometers of empty space (vacuum). All matter can radiate energy. You feel the radiation of thermal energy from a bonfire, a heat lamp and a light bulb through radiation.

Radiation A charcoal grill radiates heat to the food you are cooking because the heat is not in direct contact with the food.

Radiation For radiation to be felt as heat it must first be absorbed by a material (solid, liquid or gas) Question: Why do blue jeans feel hotter in the sun than a yellow shirt, even though they are both exposed to the same amount of sunlight? The blue jean fabric absorbs more radiant energy from the sun than the yellow shirt because of its dark color.

Conduction Radiation Convection Direct contact of particles Occurs best in a solid Transfer of energy by waves Only method that can be transferred through empty space Transfer of energy by bulk movement of matter (fluids) Currents (wind, water)

Label the parts Conduction, convection and radiation can be found in the diagram below. Label the appropriate parts.