2. Remember... Resistance in Mechanical systems (friction) opposes motion of solid objects.

3. In Fluid systems, resistance opposes the flow of fluids. In Electrical Systems, resistance opposes the flow of charge, or current.

4. In Thermal systems, resistance opposes the flow of heat. Thermal resistance is the measure of an object’s ability to oppose heat transfer.

5. Materials with low thermal resistance are used to transmit or conduct heat. The bottom of most cookware has low thermal resistance.

6. Materials with high thermal resistance are used to insulate an object or a region of space. For example, the walls of a refrigerator have a layer of insulation to increase their thermal resistance. With the insulation, there is a low heat flow rate from the warm air outside to the cold interior of the refrigerator.

7. Insulation, or high thermal resistance, is important to keep the temperature in a container constant, or to minimize the heat flow rate through a container. In addition to insulating refrigerators and homes, high thermal resistance is used to insulate water heaters, water pipes, and thermos bottles. Water supply and sewer pipes are buried, so they are insulated by soil.

8. A typical wall in a house consists of: - an inner layer of drywall, - a middle layer of 3” insulation, - and an outer layer of brick. Heat flows through each resistance, one at a time, just like the current flows through each resistance in a series circuit.

9. The total thermal resistance is calculated in the same way as the total electrical resistance: R total = R 1 + R 2 + R 3 +... So, for the wall of a house, the total thermal resistance is: R total = R drywall + R insulation + R brick