Presentation on theme: "How does Heat Energy transfer from one substance to another?"— Presentation transcript:
1 How does Heat Energytransfer from onesubstance to another?
2 If you put a hot cup of coffee into a refrigerator, would “cold” transfer from the fridge to the coffee, or would “hot” transfer from the coffee to the fridge?Hmmmm….
3 Here is how it works: Heat Energy is what makes the coffee hot. Heat is the energy transferred between objects that are different temperatures.Heat always flows from warm to cold.Since the inside of refrigerator has a lower temperature than the coffee, heat energy travels from the coffee to the refrigerator, until they reach equilibrium (the same temperature).
4 Things that affect heat transfer: Thermal Conductors: Substances that transfer thermal energy very well.Examples: Solids are better conductorsthan liquids or gases.Metals are the bestconductors
5 Things that affect heat transfer: Thermal Insulators: Substances that do not transfer thermal energy very well.Examples: Clothing, building insulation,Wood, plastic…
6 Now that we know which way heat energy travels (from hot to cold), how does it actually travel? There are three types of heat transfer:CONDUCTIONCONVECTIONRADIATION
7 Conduction Conduction is transfer through direct contact. On a molecular level, hotter molecules are vibrating faster than cooler ones.When they come in contact, the faster moving molecules “bump into” the slower moving molecules and heat is transferred!This is how heat is transferred to your finger if you touch a hot stove!
8 ConvectionWhen fluids are heated, currents are created. Hot fluids rise. Cold fluids sink.This is because the individual molecules that come in contact with a hot surface expand, become less dense, and rise. (this is how hot air balloons work!)When this happens, other molecules circulate down and take their place, and a cycle is established..
9 RadiationHeat transfer through open space. Travels through gas or empty space.Travels as an electromagnetic wave.Sometimes these waves are in the visible part of the spectrum, like when something is “red hot.” You can see how hot it is, but you can also feel it from a distance, as your skin absorbs the energy.
10 Q.) When you put a teapot on the stove to boil water, which of the three kinds of heat transfer can be observed?A.) Actually, all three!First, there is conduction between the burner and the teapot, and then conduction between the teapot and the water molecules that are in direct contact with the teapot.Next, there is convection in the water as the heated molecules of water from the bottom of the teapot rise and spread their heat energy to the cooler molecules above them through direct contact. This convection current also pushes cooler molecules of water down to the bottom where they come in contact with the heated bottom of the teapot.While all of this is occurring, heat energy is being radiated in all directions from the from the burner and is absorbed by other objects. You can feel this energy if you stand too close!