SCIENCE CH- CHANGES AROUND US (NOTEBOOK EXERCISE AND WORKBOOK EXERCISE)
CH- CHANGES AROUND US
(NOTEBOOK EXERCISE)
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NEW WORDS
irreversible
simultaneously
desirable
spade
contracts
NEW TERMS
Simultaneously: occurring at the same time
Spade: a tool with a sharp-edged, typically rectangular, metal blade
Answer the following questions in short.
a. List three main causes of change.
ANS. Pressure, heat and mixing are three actions that bring about a change in matter
b. Give two examples for each of the following. i. Man-made changes
ii. Reversible changes
a. Burning of fuel
b. Setting milk into curd
iii. Undesirable changes
a. Rotting of food
b. drastic changes in weather
c. State one difference between desirable changes and undesirable changes. (can make a table and write too the difference between)
Changes that are useful are called desirable changes. Ripening of fruits and occurrence of day and night are examples of desirable changes.
Changes that are not useful and may even be harmful are called undesirable changes. Rotting of food and drastic changes in weather are examples of undesirable changes.
6. Define the following.
a. Irreversible changes -- Changes which cannot be reversed simply by changing the conditions are called irreversible changes. These changes are permanent and we cannot get back the original substance. Examples: Setting milk into curd , Germination of a seed
b. Fast changes -- The changes that occur in a short time are called fast changes. Examples: Burning of fire crackers, Earthquakes
c. Chemical changes -- A chemical change is a change in which new substances are formed which have properties that are different from the original substances. Both the physical and chemical properties of a substance change during a chemical change. Examples: Digestion of food, leaves changing colours during fall.
7. Give reasons.
a. Digestion is a chemical change as well as a physical change.
Ans. Digestion is another example of physical and chemical changes occurring simultaneously. Food is physically broken down by chewing and chemically broken down by digestive enzymes in the saliva and the acid in the stomach.
b. Metals are used for making tools.
Ans. The property of solids to expand and contract on cooling is used in making tools. So, Metals are used for making tools. Also they can be strong and easy to shape too.
8. Answer the following questions in detail.
a. How is the melting of wax different from the burning of wax?
Ans. The melting of wax is a physical change. The production of carbon dioxide and water vapour (new substances) during the burning of wax is a chemical change.
b. How does mixing bring about a change? Explain with the help of an example.
Ans. When two or more substances are mixed, they may form a mixture or react with each other to form a new substance.
Some examples of changes due to mixing are:
• When salt is mixed with water, it forms a salt solution. The salt can be recovered back from the solution by evaporation.
• When we add baking soda to vinegar, it results in the release of carbon dioxide which is an entirely a new substance and the initial substances cannot be recovered back.
c. Why are gaps left between railway tracks?
Ans. The gaps are left purposely, to allow the expansion of the metal during summer. Otherwise, the tracks would bend and may cause accidents.
Note: Q.11, 12 attempt by your own
WORKBOOK EXERCISE LINK (Upload on between us)
https://drive.google.com/file/d/175LUlYYuzg9Qos3YThihUjx9xxVOCNO2/view?usp=sharing
