Heat Transfer. Conduction Radiation Convection

Transcription

1 Heat Transfer Conduction Radiation Convection

2 Real World Experience We are going outside to experiences heat transfer. Instructions: while outside place hand on the concrete. Note whether it feels cold or hot.

3 Transfer Heat Thermal energy is ALWAYS transferred from the warmer object to the cooler object. This is what we call HEAT TRANSFER. WARM COLDER What is being transferred? THERMAL ENERGY

4 Heat Transfer in the Real World If the concrete feels cold which way is the heat energy going? Heat is being transferred from your hand to the concrete If the concrete feels hot which way is the heat energy going? Heat is being transferred from the concrete to your hand

5 Heat Heat (heat transfer): It is the movement of thermal energy It flows because of differences in temperature. Only called heat during the transfer process or while it is flowing. Otherwise, it s thermal energy.

6 Thermal Energy CZ1cY (2:30-3:30) Thermal Energy is the internal energy of an object due to the kinetic energy of its atoms and/or molecules as they vibrate. The atoms and/or molecules of a hotter object have greater kinetic energy than those of a colder one.

7 Magic Squares Here are two black squares that are the same size. Which will melt the ice cube fastest? Why? Which one melted the fastest? Why? Both are black and absorb heat energy from their environment, but what makes the metal one work better? To understand that we need to understand conduction

8 Conduction CZ1cY (10:20 to 12:33) Conduction: the transfer of heat through matter by communication of kinetic energy from particle to particle with no net displacement of the particles ( definition 2) In other words the molecules are playing hot potato where the thermal energy is the potato and the molecules are pretty much staying in a certain area.

9 Conduction

10 How Conduction works The two objects must be touching, so that the vibrating molecules of the first object will bounce against the molecules of the second object and get them vibrating just as fast. The vibrations transfer from molecule to molecule until all molecules in both objects are vibrating at the same rate.

11 Magic Square Explanation Metals have lose electrons in their outer shells that are more easily able to transfer vibrations easily. It is these electrons and the close packing of the molecules in metals that allow thermal energy to be transferred very quickly from hot to cold spots. Plastics don t transfer thermal energy as quickly because of its insulating spaces. It doesn t allow the thermal energy to transfer very quickly, instead it slows it down.

12 Real World Experience What is a hot plate? How does it work? Putting a hand above it, so not to touch the coils, what does it feel like? Why can you feel heat? Radiation 6vc

13 Radiation Radiation: - energy that comes from a source in the form of waves or rays you cannot see (

14 Radiation in action 1. The molecules of the first object vibrate and cause electromagnetic disturbances. 2. Travel through space as Electromagnetic waves 3. These EM waves then impact the second object and are absorbed, causing the molecules of the second object to vibrate

15 Convection Convection: the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.

16 Summary Thermal Energy is the internal energy of an object due to the kinetic energy of its atoms and/or molecules as they vibrate. Heat transfer or Heat is when thermal energy is moved from a colder object to a warmer object. Three ways to move thermal energy Conduction: direct contact of molecules Radiation: heat energy moving through space as waves Convection: the circulation of a material because of different density due to different temperature and the effects of gravity.

17 WARM COLDER What is being transferred? Thermal Energy