In this chapter, we’ll delve into the fascinating world of natural phenomena that occur around us every day. We’ll explore the changes that take place from day to night and from night to day, the rising and setting of the sun and moon, and the fluctuations in climate.
We’ll also examine slower transformations, such as the gradual melting of ice and the evolution of ecosystems over time. With so much to discover, let’s embark on this exciting journey of exploration and learning!
CBSE Class 6 Science Notes Chapter 6 Changes Around Us
The different topics covered in CBSE Class 6 Science Chapter 6 are tabulated below:
| Ex-6.1 | Can All Changes Always Be Reversed? |
| Ex-6.2 | Could There Be Other Ways To Bring A Change? |
Ex. 6.1 – Can All Changes Always Be Reversed?
Heating can cause various changes to an object, such as:
- Some objects get hot without any other noticeable changes.
- Other objects may expand in size when heated.
- Some objects may start to burn.
- Certain objects might undergo a change in their physical state, such as melting or vaporizing.
Applying force or pressure to an object can lead to various changes, such as:
- Altering its shape or size.
- Compressing air.
- Hammering metals into thin sheets.
- Stretching elastic materials.
- Spinning cotton into thin threads.
Chemical changes:
Chemical changes occur when the chemical properties of a substance change, resulting in the formation of a new substance. Cooking food is an example of a chemical change.
The characteristics of chemical changes are:
- The properties of the products formed are different from the properties of the reactants.
- Most chemical changes are irreversible, meaning that the original substance cannot be recovered.
- Chemical changes always involve energy changes, such as the release or absorption of heat, light, or sound.
Physical changes:
Physical changes refer to changes in the physical properties of a substance without the formation of any new substances. Examples of physical changes include melting, freezing, or changing the shape or size of an object.
The characteristics of physical changes are:
- No new substances are formed during the process.
- The products remain identical to the reactants in terms of their chemical properties.
- Physical changes are typically reversible, meaning that the original substance can be restored by reversing the conditions that led to the change.
Reversible changes:
Reversible changes are those that can be reversed by applying an appropriate condition or process. For instance, stretching a rubber band can be reversed by releasing the tension.
Irreversible changes:
Irreversible changes are those that cannot be undone or returned to their original state. Burning a piece of paper is an example of an irreversible change as the original paper cannot be recovered once it has been burned.
Ex. 6.2 – Could There Be Other Ways To Bring A Change?
Melting:
Melting is the process by which a solid substance transforms into a liquid state when heated.
Melting point:
The melting point refers to the specific temperature at which a solid begins to melt and transition into a liquid phase.
Freezing:
Freezing, on the other hand, is the process in which a liquid substance changes into a solid state, typically by reducing its temperature.
Changes:
Numerous changes occur in our surroundings either spontaneously or through our intervention. For instance, flowers bloom and eventually wither away as a natural process. We can also initiate changes, such as altering the size of a balloon by blowing air into it.
Natural changes:
Natural changes refer to the changes that transpire in nature autonomously. Examples of natural changes include the transition from day to night and the changing of seasons.
Slow changes:
Slow changes are those that transpire over an extended period. These changes require more time to become apparent. Examples of slow changes include the rusting of iron and the decay of teeth.
Contraction:
Contraction is the process by which an object decreases in size or shrinks.
Evaporation:
Evaporation is the process in which a liquid substance transforms into vapor.
Expansion:
Expansion is the process by which an object increases in size. For example, metals expand when heated.
Separation :
The separation of components within a mixture or impure substance is performed with the following objectives:
a. To eliminate unnecessary or harmful components.
b. To obtain the desired or useful component.
c. To eliminate impurities and obtain a pure sample.
Conclusion :
- Changes occur both in our surroundings and within ourselves.
- Certain changes are reversible, while others are irreversible.
- Changes can be categorized as either physical or chemical.
- When a material is heated, it undergoes expansion.
- Conversely, cooling a material leads to contraction.
- Among different states of matter, gases exhibit the greatest expansion, while solids exhibit the least.
- On the other hand, gases experience the most significant contraction, while solids experience the least.
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