Thermal Expansion

1. Thermal Expansion By: Rawan Al-Yousef & Alaa Sultan

2. Thermal Expansion • When ever a steel bar or a concrete is heated, its volume will slightly increase. • This is known as Thermal Expansion

3. Types of Expansion There are 3 types of Expansion: • Expansion of solids. • Expansion of liquids. • Expansion of gases.

4. Expansion of Solids • The kinetic theory explains thermal expansion as follows. When, say, a steel bar is heated its particles speed up. Their vibrations take up more space, so the bar expands slightly in all directions. If the temperature falls, the reverse happens and the material contract(gets smaller).

5. Example • A good example of solids expansion is a Bi-metallic strip. • Thin strips of two different metals are bonded together. When heated, one metal expands more than the other, which makes the bimetal strip bend. Bimetal strips are used in some thermostats-devices for keeping a steady temperature.

6. Expansion of Liquids • Liquid also expands for the same reason. However, since liquid particles are usually less tightly bound to each other molecules, they generally move further than solid particles when heated. Hence, liquid expands more than solid if the temperature rise is the same.

7. Expansion of gas • According to the kinetic theory, a gas is made up of tiny, moving particles. These move about freely at high speed and bounce off the walls of their container. The higher the temperature, then on the average, the faster they move.

8. Use of Thermal Expansion • Thermal expansion can be used in bimetallic strips in thermostats. • A thermometer works by using the thermal expansion of a liquid to measure temperature. • A hot-air balloon uses the thermal expansion of air to generate lift