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Changes Around Us (Expansion of Materials (Expansion in solids (Railway…
Changes Around Us
Expansion of Materials
Expansion in solids
Railway tracks consist of two parallel metal rails joined together. small gaps, called expansion gaps, are deliberately left between the rails as there is an expansion of the rails in hot weather.
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Expansion in liquids
Mercury expands on heating. Take a glass of water in a container and heat it . Now , dip the tip of the thermometer in the hot water. The mercury level rises up due to the expansion of mercury.
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Expansion in gases
If you keep an inflated balloon in the sun for some time, what will happen? It will grow in size as the air inside it expands on taking heat from the surroundings
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Contraction of Materials
Contraction in solids
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.
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Contraction in liquids
We observed that mercury expanded on heating. Can you say what will happen if the thermometer is allowed to cool down? The Mercury level will go down. This is because of contraction.
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Contraction on 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.
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Physical Changes
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Examples : Powdering of Sugar, Slicing, Shredding, Grating Fruits and Vegetables, And making Jewellry Out of Gold
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Chemical Changes
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Examples : Burning of Match Sticks, Rusting Of Iron , Cooking of Food, And Candle to Candle Wax
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