Chapter 11- Thermal(heat) energy transfer

Insulation

- A substance that reduces the transfer of thermal energy - Insulation means creating a barrier between the hot and the cold object that reduces heat transfer by either reflecting thermal radiation or decreasing thermal conduction and convection from one object to the other. Depending on the material of the barrier, the insulation will be more or less effective. - They are poor conductors of heat and have a low thermal conductivity. (thermal conductivity is the heat energy transferred per unit time and per unit surface area, divided by the temperature difference.) - An Insulator is a substance that transmits heat very poorly.

Demonstrating conduction

- Compare different metals using metal rods - The metal rods are all the same size - Each rod has a blob of wax at one end - They are all heated equally at the other end - The best conductor is the metal on which the wax melts first (or) - connect a coin with wax to one end of the rod - and heat the other ends - each rod has to be equally heated - the coin that falls down first is the best conductor of heat

Conduction

- Conduction is the transfer of energy in the form of heat or electricity from one atom to another within an object by direct contact. Conduction occurs most significant in solids and less though in liquids and gases because the particles are closely packed together in a solid there for allowing vibrations to travel on from one atom to another - It is the transfer of thermal energy through direct contact - It is also the flow of heat through matter from places of higher temperature to places of lower temperature without movement of the matter as a whole. (it allows heat to move easily through them.) - It is the process by which heat energy is transmitted through collisions between neighboring atoms or molecules. The fire's heat causes molecules in the pan to vibrate faster, making it hotter. These vibrating molecules collide with their neighboring molecules, making them also vibrate faster. - Conductors are substances that transmit heat. - liquids can also conduct heat because there particles are in close proximity - However convection is more important that conduction in the transfer of heat through a liquid

Radiation

- Energy that is radiated or transmitted in the form of rays or waves or particles. - The transfer of energy by electromagnetic waves - Electromagnetic radiation: energy traveling in the form of waves - The hotter an object the more infrared radiation it gives out - infrared radiation: Electromagnetic radiation whose wavelength is greater than that of visible light; sometimes known as heat radiation Characteristics of infrared radiation: - is produced by warm or hot objects - is a form of electromagnetic radiation - Travels through empty space and air in the form of waves - travels in straight lines - Warms the object that absorbs it - is invisible to the naked eye - can be detected by nerve cells in the skin

Convection

- Process by which, in a fluid being heated, the warmer part of the mass will rise and the cooler portions will sink. - The transfer of heat by the movement of a fluid - The transfer of thermal energy by the circulation or movement of a liquid or gas - When a fluid, such as air or a liquid, is heated and then travels away from the source, it carries the thermal energy along. This type of heat transfer is called convection. The fluid above a hot surface expands, becomes less dense, and rises. - The transfer of heat energy through a material by movement of the material itself

Demonstrating convection

- The hot water in the styrofoam cup heats up the water and food dye directly above it, making the molecules here move faster as they gain heat energy. This group of fast moving molecules flow upwards in the water (because they are less dense than the surrounding cooler water). They take heat energy with them, and are moving by "convection". The visualized convection currents are beautiful as they trace out the curving patterns of heated water. Convection is the movement of a group of higher-energy molecules through a liquid, or a gas. Convection is how heat moves around the air in the classroom

Explaining convection

- results in expansion of a fluid when it is heated expansion meaning: 1. an increase in volume - while mass stays constant 2. density decreases - a less dense material is lighter and is pushed upwards by the surrounding denser material - The particles in the hotter fluid have more kinetic energy - they move around faster and take this energy with them as they flow from place to place - fluid itself moves, carrying energy with it.

Demonstrating poor conductors of heat

Demonstrating how water is a poor conductor of heat - lumps of ice at the bottom of the test tube are held in place by a wired gauze - The water is heated close to the mouth of the tube - The water boils while the ice remains frozen - Heat hasn't conducted to the bottom of the tube - The water at the bottom remains cold and the ice does not melt