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Changes Around Us: Class 6 Chapter 6 Science Notes

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Changes Around Us: Class 6 Chapter 6 Science Notes

Changes Around Us Class 6 CBSE Notes: Class 6 Science chapter 6 “Changes Around Us” explains how the environment around us changes due to various processes.

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Changes Around Us Class 6 Chapter 6 Science Notes

We encounter different types of changes every day. Turning day into night, night into day, rising and setting of the sun and moon, changing of climate, melting of ice, and a lot more. It may take a minute for these changes to occur, or it may take a little longer. There are very few changes that are even noticeable.

What is Change?

Any alteration of a substance from its original shape, size and state is known as a change. Some changes can be reversible and some can be irreversible.

  • Reversible Change: It is a change that can be undone or reversed. Usually, there is a change in physical properties, shape and size of the material. For example: Melting of ice and inflation of a balloon.
  • Irreversible Change: An irreversible change is when something cannot be changed back to its original form. Formation of new substance is involved in this change. For example: Burning of paper and cooking of food.

What are the two types of Changes?

  1. Physical Change: A change in which a substance undergoes a change in its physical properties such as shape, size, and volume, colour, and appearance, state of a substance (solid, liquid, and gas) is termed physical change. Example: Boiling water, mixing sand and water, melting an ice cube, freezing water etc.

Physical changes are usually reversible.

  1. Chemical Change: A change in which one chemical substance is transformed into one or more different substances is termed as chemical change.

Example: Burning wood, souring milk, mixing acid and base, rusting of iron etc.

Chemical changes are usually irreversible.

What are some of the factors leading to Change?

Expansion and Contraction

  • When the temperature increases, the particle of a substance expands or becomes loose, so the object becomes bigger in size. When this happens, the material is said to undergo expansion.
  • When the temperature decreases, the particles of substance contracts or becomes tight. When this happens, the material is said to undergo contraction.
  • The amount of expansion or contraction varies in solids, liquids and gases.
  • Substances or materials undergo physical changes when they change states.
  • Water is a classic example as it can exist as solid, liquid or gas.
  • The solid state of water at very low temperatures is known as ice The solid state of water at very low temperatures is known as ice. When heated or heated to a higher temperature, ice melts into water. The physical change when a solid change to liquid is called Melting.
  •  If we keep increasing the temperature, the water now starts to boil until it fully becomes water vapour. The physical change when a liquid changes to gas is called Evaporation.
  • To get back the water from water vapour, it is possible by Condensation– a physical change where the gas changes to a liquid. This is possible by lowering the temperature.

An abnormal expansion of water

Water on cooling contracts upto 4 degree C. On further cooling, up to 0 degree C, water expands rather than contracting with a decrease in temperature. This means that as the temperature decreases from 4 degree C to 0 degree C, water expands. This behavior is called the anomalous expansion of water.

Burning

Burning is an irreversible change where a substance burns to produce new material. These new materials are ash and some gases.

For example: Burning paper produces ash, which differs in appearance and properties from paper.

Separation

The separation of the components of a mixture or an impure substance is carried out with the following purposes:

  1. To remove the unusual or harmful component.
  2.  To obtain the useful component.
  3. To remove impurities for getting a pure sample.

Examples of Changes Around Us

  1. Change in weather.
  2. There is a constant change in crops in the field.
  3. Flowers bloom and then wither away.
  4. Change in day and night.
  5. Change in the shape of the moon in a month.
  6. Seasonal changes throughout the year.
  7. Changes taking place in our body like growing of nails, hair, and height.
  8. Rusting of iron.

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