Factors affecting contraction process Definition Contraction is the

Factors affecting contraction process

Definition : • Contraction is the reverse process. When heat is applied to a body, the rate of vibration and the distances between the molecules composing it are increased and, hence, the space occupied by the body, i. e. , its volume

Contraction in solids: • Contraction in solids. Contraction in liquids. • Contraction in gases if we hold a very hot glass tumbler under cold water, it cracks. • This is because the outer surface of the glass comes in direct contact with cold water and contracts more as compared to the inner surface.

Contraction in liquids: • contraction of liquid observed that water expanded on heating. Can you say what will happen if the water is allowed to cool down and then poured back into the glass? • Would it still overflow? No. This is because of contraction.

Contraction in gases: • Contraction in gases If an inflated balloon is tied at the mouth of a bottle and the bottle is placed in ice-cold water, what will happen? • The balloon will shrink in size, as the air inside the balloon contracts on cooling.

Factor affecting the expansion process Change in the dimensions (s)of a substance due to change in temperature. increase in size of any object like solid, liquid and gas on heating is called thermal expansion.

There are three types of expansion in solid • Linear expansion • Superficial expansion • Cubical expansion Linear expansion Increase in length of any solid on heating is called linear expansion.

Superficial expansion Increase in area on heating is called superficial expansion

Cubical expansion Increase in volume on heating is called cubical expansion

Application of expansion and contraction of solids in everyday life

Application of expansion and contraction of solids in everyday life In our daily life, we pay special attention avoid the harmful effects of thermal expansion and contraction of solids, the techniques used in different projects may be explained by the following examples: • Expansion gaps in concrete roads • Railway tracks • Expansion of bridges • Overhead power lines and telephone wires • Large bends in pipes

Expansion Gaps in Concrete Roads In hot summer season, the concrete used to build roads expands making cracks in the surface of road. To avoid such damage, small gaps are left after every few meters in the construction of concrete roads or footpaths.

Railway Tracks Gaps left between two sections of a railway track. Which allows expansion and contraction of rails during summer and winter seasons. If there are no gaps in the sections of railway tracks, they may de-shape due to expansion in summer.

Expansion of bridge Iron girders are used in the construction of bridges. In summer and winter seasons they expand contract. One end of each girder id fixed while the other end rests on the rollers. A gap is also left at this end. In this way the girder can move forward or backward during expansion or contraction. Expansion gap avoid the damaging of bridge.

Overhead power lines and telephone wires Overhead telephone and electricity wires installed on poles expand during hot weather and contract in cold weather. The wires between two poles are given a certain amount of sag so that they may contract in winter avoid snapping.

Large Bends in pipes The pipes through which hot or cold liquid or gas flows are often given bends so that they may expand or contract avoid cracking.

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