NCERT Class 6 Science Chapter 6: Changes around Us YouTube Lecture Handouts

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Obvious Changes

• Plants grow

• Leaves fall

• Flowers bloom and wither away

• Nails, hair, weight grows

Reversible Versus Irreversible

• Experiment of Balloon / Rubber band

• Inflate and deflate (changes are reversible)

• Cut the paper – irreversible change

• Burning of Candle versus melting of wax - The candle of same length cannot be obtained again i.e., change in length of candle cannot be reversed. Hence, burning of candle is not reversible but melting of wax is reversible.

• Dough and make chappati & bake on tawa

• Potter bakes the pot in an oven

• Blacksmith – making iron tools, iron is heated till it becomes red hot

• Changes

• Reversible – add salt to water

• Irreversible – add tea leaves to water

Expansion and Contraction

Heating and cooling an iron wheel to fix it on a wooden wheel (metal rim is smaller than the wooden wheel)

• Iron Tools: Normally, the ring is slightly smaller in size than the wooden handle. To fix the handle, the ring is heated and it becomes slightly larger in size (expands).

• Now, the handle easily fits into the ring. When the ring cools down it contracts and fits tightly on to the handle.

-Mayank