# 32: Thermal Expansion

{'English - US': '/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-32/lec32.srt'}

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Topics covered: Heat raises the temperature, and usually the volume of the material that absorbs the heat. The linear and cubical thermal expansion coefficients of metals (including mercury) are described and demonstrated. Ice is discussed as a special case.

Instructor/speaker: Prof. Walter Lewin

Date recorded: December 1, 1999

## Video Index

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• Heat and Temperature
Various temperature scales are discussed: Celsius, Fahrenheit, Kelvin.

• 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.

• Cubical Thermal Expansion
The fractional change in volume with temperature is given by the coefficient of cubical expansion. A mercury thermometer is discussed.

• 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".

• 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.