Lecture 32: Heat - Thermal Expansion

**[[https://www.surveymonkey.co.uk/r/6DMBC3Q|>>PLEASE TAKE A QUICK SURVEY<<]]** **1. Heat and Temperature:** Various temperature scales are discussed: Celsius, Fahrenheit, Kelvin. **2. Linear Thermal Expansion:** The linear thermal expansion coefficient is introduced. Expansion leads to a need for expansion joints in railroad rails to avoid bulging on hot days. Thermal expansion is demonstrated by heating and cooling a brass rod. An important application of thermal expansion is bi-metals which are used in thermostats, safety devices and thermometers, as demonstrated. **3. Cubical Thermal Expansion:** The fractional change in volume with temperature is given by the coefficient of cubical expansion. A mercury thermometer is discussed. **4. Shrink Fitting:** Shrink fitting is a technique that makes use of the thermal expansion by heating one object (of two). After the two objects are assembled, they cool, and the fit is perfect and "for ever". **5. Cubical Thermal Expansion of Water:** Water has a maximum density at 4 degrees Celsius; between 0 and 4 degrees Celsius the cubic thermal expansion coefficient is negative so the water expands as it cools below 4 degrees Celsius. The density of ice is about 8% lower than water, so ice cubes and icebergs float in water.