Chapter 1
MATTER IN OUR SURROUNDINGS

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Q1. Which of the following are matter?

Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume

🧠 Answer:
✅ Matter (has mass and occupies space):

• Chair, air, almonds, lemon water, smell of perfume
  
  

❌ Not Matter (no mass, no space taken):

• Love, smell (as emotion), hate, thought, cold (as sensation)
  
  

🎤 How to explain engagingly in class:

“Can you touch love? Bottle a thought? Store hatred in a jar? No. But you can feel them. They're real, but not matter. Now perfume — that’s matter, because it spreads and occupies space!”

Q2. Why does hot food’s smell reach farther than cold food?

🧠 Answer:

Particles in hot food have more energy, so they move faster.
This leads to faster diffusion of aroma particles in air.

🎤 Say in class like this:

“Hot food releases aroma particles like sprinters — zooming across the room! Cold food? More like sleepy joggers… slow and lazy.”

🧪 Optional: Spray perfume near one corner, ask students to raise hands as they smell it. Then explain diffusion.

Q3. A diver can cut through water — which property of matter?

🧠 Answer:

This shows that particles of matter have space between them.

🎤 In class:

“Imagine water particles as a group of dancers — not standing tightly packed like bricks, but with gaps. The diver slips through those gaps like a fish.”

💡 (You can even mime this with your hands.)

Q4. What are the characteristics of the particles of matter?

🧠 Answer:

1. They have space between them
   
   

2. They are constantly moving
   
   

3. They attract each other
   
   

🎤 Teaching Tip: Turn it into a chant or hand movement

“Particles — have space (open hands), they move (wiggle), and they stick (clap). Say it with me!”

Perfect, Mayank! These are excellent classroom discussion and assessment questions that can deepen student understanding of States of Matter and Properties of Matter. Here's how you can integrate these questions into your lecture on States of Matter, making the lesson more interactive, conceptual, and student-friendly:

🧪 Enhanced Lecture Add-on: States of Matter – With Q&A & Concept Checks

🔄 RECALL: What is Density?

📘 Definition:

“Density is the mass per unit volume of a substance. It tells us how much matter is packed into a given space.”
📏 Formula: Density = Mass / Volume

🧠 Question 1: Arrange in Increasing Order of Density

Substances:
Air, exhaust from chimneys, honey, water, chalk, cotton, iron

📌 Ask your students to think:

“Which feels heavier in your hand – cotton or iron?”
“Which flows faster – honey or water?”

💡 Expected Answer (Increasing Order):
Air < Exhaust < Cotton < Water < Honey < Chalk < Iron

🧊 Question 2(a): Tabulate the Differences in States of Matter

Create a simple table on the board or show it digitally:

Characteristic             Shape                          Volume                    Compressibility           Fluidity          Kinetic Energy                Density

Solid                            Fixed                            Fixed                          Negligible                       No               Lowest                            Generally High

Liquid                           No fixed                      Fixed                            Slight                            Yes              Moderate                        Moderate

Gas                              No fixed                       Not fixed                     High                                Yes             Highest                           Lowest

💬 Question 2(b): Explain the Terms

Give each student one word to explain (in pairs or groups):

• Rigidity – Ability to resist shape change (high in solids)
  
  

• Compressibility – Ability to be squeezed (high in gases)
  
  

• Fluidity – Ability to flow (liquids and gases)
  
  

• Filling a gas container – Gases spread and occupy entire space
  
  

• Shape – Solids have fixed shape, others take container shape
  
  

• Kinetic Energy – Movement energy; highest in gases
  
  

• Density – Mass per unit volume; generally solids > liquids > gases
  
  

💥 Question 3: Conceptual Reasoning

💬 (a) Why does a gas fill the container?
✅ Gas particles move fast and have weak attraction → spread in all directions.

💬 (b) Why does a gas exert pressure?
✅ Constant motion → Particles collide with container walls → Pressure.

💬 (c) Why is a wooden table a solid?
✅ Has a fixed shape and volume, doesn’t flow or compress → classic solid behavior.

💬 (d) Why can we move hand in air but not in wood?
✅ Air particles are far apart (low density, weak attraction) → easy to move through.
✅ Wood particles are tightly packed (strong attraction) → needs force!

❄️ Question 4: Why Does Ice Float on Water?

🎯 Ask Students First:

“Is ice heavier or lighter than water?”

📘 Conceptual Explanation:

Ice is a solid form of water, but its structure forms open spaces (due to hydrogen bonding) → it becomes less dense than water.
✅ Less dense objects float in denser liquids.

💡 So, ice floats on water!

Q1. Convert the following temperatures to Celsius scale:

📘 Formula:
°C = K – 273

a. 300 K
✅ °C = 300 – 273 = 27°C

b. 573 K
✅ °C = 573 – 273 = 300°C

Q2. What is the physical state of water at:

a. 250°C
✅ Water will be in the gaseous state (steam), since this is well above boiling point (100°C).

b. 100°C
✅ Water will be in a liquid + gaseous state (both can exist at this point). This is the boiling point, where liquid starts converting into gas.

Q3. For any substance, why does the temperature remain constant during the change of state?

✅ The temperature remains constant during a change of state because the heat energy is used to break the intermolecular forces between the particles, not to increase temperature.

This hidden heat is called latent heat (of fusion or vaporisation), and it helps the particles change their state (like from solid to liquid or liquid to gas) without a rise in temperature.

Q4. Suggest a method to liquefy atmospheric gases.

✅ Atmospheric gases (like oxygen, nitrogen) can be liquefied by:

• Increasing pressure
  
  

• Lowering temperature
  
  

🎯 These two conditions bring gas particles closer together and reduce their energy, making them change into liquid form.

💡 This method is used to store gases like LPG, CNG, and oxygen in compressed cylinders.

Would you like a practice worksheet with similar questions for your students?

Here are clear and concise answers to each of the questions based on the concepts of evaporation and cooling from the Class 9 CBSE Science syllabus:

1. Why does a desert cooler cool better on a hot dry day?

✅ On a hot, dry day, the temperature is high and the humidity is low.
These conditions make evaporation faster, and since evaporation causes cooling, the desert cooler works more efficiently and gives better cooling.

2. How does the water kept in an earthen pot (matka) become cool during summer?

✅ The earthen pot has tiny pores that allow water to seep out and evaporate.
During evaporation, the escaping water particles take heat energy from the remaining water, making it cooler.
Hence, the matka cools the water naturally.

3. Why does our palm feel cold when we put some acetone, petrol, or perfume on it?

✅ These liquids are volatile and evaporate quickly.
As they evaporate, they absorb heat from the skin (palm), which results in a cooling effect, making your palm feel cold.

4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

✅ A saucer has a larger surface area than a cup.
Greater surface area speeds up evaporation, which helps the hot tea or milk cool down faster, making it easier to sip.

5. What type of clothes should we wear in summer?

✅ We should wear light-colored, cotton clothes in summer because:

• Light colors reflect heat.
  
  

• Cotton absorbs sweat and exposes it to the air, where it evaporates, removing heat and cooling the body.