This PSEB 6th Class Science Notes Chapter 6 Changes Around Us will help you in revision during exams.
PSEB 6th Class Science Notes Chapter 6 Changes Around Us
→ Change is an act by which a thing becomes different from its previous one.
→ We see many changes around us and every change is important in a positive or negative way.
→ Changes can be grouped together by finding similarities and differences between them.
→ All the changes can be broadly divided into two types i.e. natural and manmade.
→ Changes that occur in nature and do not require our involvement are called natural changes. These are never ending changes.
→ Examples of natural changes include melting of snow, falling of leaves from trees, etc.
→ Changes occurring due to the efforts of human beings are called artificial or manmade changes.
→ Examples of manmade changes include preparing chapattis from wheat flour, cooking vegetables, etc.
→ Based on the speed, we can classify changes into two categories. These are slow changes and fast changes.
→ Slow changes are those which take more time to happen. For example, growing of tree, a baby becoming an adult, etc.
→ Fast changes are those that happen very fast. For example, burning of match sticks, bursting of crackers, etc.
→ Out of all the changes around us, only a few changes can be reversed. These are called reversible changes.
→ The changes which cannot be reversed are called irreversible changes.
→ A change in a substance is called reversible if we can get the substance in its original form by changing the conditions.
→ For example, ice changes to water on melting and water can be changed into ice by cooling, is a reversible change.
→ A change in a substance is called irreversible if we cannot get the substance in its original form by changing the conditions.
→ For example, roti once prepared on Tawa, cannot be changed back to dough again.
→ Some changes are periodic whereas others are non-periodic.
→ Changes that are repeated after regular intervals of time are called periodic changes.
→ For example, change of day and night, swinging of pendulum of a clock, the beating of heart, change of seasons.
→ Changes that are not repeated after a regular interval of time are called non-periodic changes.
→ For example, the occurrence of earthquakes, the occurrence of rain, etc.
→ We have classified changes into physical and chemical changes.
→ Any temporary change in which no new substance is formed and the chemical composition of the original substance remains the same is known as physical change.
→ During physical changes, physical properties like colour, shape, size, state, etc. may change. Therefore, we can say that Physical change is a reversible change.
→ Any permanent change in which new substances are formed. These have physical and chemical properties completely different from those of the original substance.
→ Physical changes are mostly reversible in nature whereas chemical changes are mostly irreversible changes.
→ Expansion and contraction are physical changes that are very useful in our daily life.
→ In the expansion the dimensions of the substance increase and in contraction the dimensions of the substance decrease.
→ Change: An act by which a thing becomes different from its previous one.
→ Natural changes: Changes that are occurring naturally and are never-ending are called natural changes.
→ Manmade changes: Changes that are occurring due to the efforts of human beings are called manmade changes.
→ Periodic change: Changes that are repeated after regular intervals of time are called periodic changes.
→ For example, change of day and night, swinging of pendulum of a clock, beating of heart, change of seasons.
→ Non-periodic changes: Changes that are not repeated after regular intervals of time are called non-periodic changes.
→ For example, the occurrence of earthquakes, the occurrence of rain, etc.
→ Reversible change: The changes which take place in a substance and can be reversed to their original state are called Reversible changes.
→ Irreversible change: The changes which cannot be reversed to the original substances are called Irreversible changes.
→ Physical Change: Physical change is a temporary change in which no new substance is formed and the chemical composition of the original substance remains the same.
→ Chemical change: Chemical change is a permanent change in which new substances are formed whose physical and chemical properties are completely different from those of the original substance.
→ Expansion: When a substance increases its size on heating then the change is called expansion.
→ Thermal expansion: When the expansion is due to an increase in temperature it is called thermal expansion.
→ Contraction: When a substance decreases its size on cooling then the change, is called contraction.
→ Evaporation: When a liquid changes into the gaseous form on heating or on decreasing pressure then the process is known as evaporation.
→ Melting: When a solid changes into liquid form on heating or on increasing pressure then the process is known as melting.