Conduction, Convection, Radiation

• Conductive heat transfer is the process by which energy is transferred from one object to another through direct contact.
• Metals are good conductors because they have many free electrons that can carry heat quickly.
• Heat loss increases as surface area increases.
• Thermal insulators like air or foam reduce heat flow by trapping pockets of still air between molecules.
• Materials with high thermal conductivity allow more heat to pass through them than those with low thermal conductivity.
• The rate at which an object loses heat depends on its temperature difference relative to its surroundings.
• convection is the method of heat transfer by fluids
• radiation is the emission of heat by hot bodies
• In convection currents, warmer particles rise while colder ones sink
• an insulator is a material that doesn't allow thermal energy to be transmitted through it easily
• All objects emit radiant energy
• a conductor allows thermal energy to flow freely through it
• the amount of radiation emitted from an object depends on its surface area and temperature
• A black body absorbs all wavelengths of light equally well
• The rate at which an object emits radiation depends on its temperature and surface area (more s.a = more radiation emitted/absorbed)
• A good conductor will conduct heat quickly from one end to another
• the higher the temperature, the more radiation is given off
• Conductors are materials with high electrical conductivity such as metals like copper or aluminum.
• Conductors are good conductors because they have many free electrons that can move around quickly when heated
• Insulators are bad conductors because their atoms are tightly packed together so there aren’t any free electrons available to carry heat away.
• Conductors are materials that allow heat to pass easily through them.
• When a metal is heated, these electrons gain kinetic energy and collide more frequently with neighbouring atoms causing them to vibrate faster.
• Thermal insulators prevent heat loss or gain by reducing the rate of heat transfer between two objects.
• Insulators have low thermal conductivity so they do not transfer heat easily between molecules within them.
• Thermal insulation works by trapping air pockets within it, which reduces the amount of heat transferred by convection.
• The air trapped inside wool fibres acts as a barrier against heat flow, making it an effective insulating material.
• Foam rubber has tiny pockets filled with gas which act as barriers to slow down the movement of heat molecules.
• The air inside your home acts as an insulating layer preventing heat from escaping during winter and keeping cooler temperatures out during summer.
• A vacuum is even better than air at stopping heat flow because there are no particles to bump into one another and transmit heat.
• Increasing the thickness of an insulator increases its effectiveness at preventing heat transfer.
• What affects energy flow in an object?

  Temperature, material, and surface area.
• Why do metals feel colder than wooden surfaces?

  Metals are conductors so they remove heat from our hands at a faster rate, so our hands cool down! The temp in our bodies is actually the same
• Why do metals conduct faster?

  Because of more free delocalized electrons
• How is heat energy transferred from hot to cooler places by convection?

  Liquids and gases expand when heated, as particles move faster, become less dense and take up more volume ( the gap between the particles expands. Hot areas are less dense, so they rise into the cold areas, and the denser cold falls into the warm areas. Convection current formed.
• Radiant energy travels through space without any medium. It does not need anything to carry it like conduction or convection. It travels in straight lines until it hits something else. If nothing absorbs it then it will continue forever. It has no mass but still carries energy.
• dull, matt or rough surfaces have good absorbtion, good emission and bad reflection
• shiny surfaces have poor absorbtion, poor emission and good reflection
• black body is an object that absorbs all radiation falling on it and emits maximum amount of radiation possible
• white surfaces have poor absorption, poor emission, good reflection
• how do hot air balloons rise (convection)?

  When the air inside is heated, the particles gain energy and spread out and the air becomes less dense and takes up more volume. The surrounding colder, denser air falls beneath the hot air, forcing the hot, less dense air to rise, pushing up the balloon with it and creating a convection current.