NCERT Class 9 Science Textbook for Blind and Visually Impaired Students made Screen Readable by Professor T K Bansal.

1.2.1 PARTICLES OF MATTER HAVE SPACE BETWEEN THEM

In Activities 1.1 and 1.2 we saw that particles of sugar, salt, Dettol, or potassium permanganate got evenly distributed in water. Similarly, when we make tea, coffee or lemonade (nimbu paani), particles of one type of matter get into the spaces between particles of the other type. This shows that there is enough space between particles of matter.

1.2.2 PARTICLES OF MATTER ARE CONTINUOUSLY MOVING

Activity 1.3

• Put an unlit incense stick in a corner of your class room. How close do you have to go near it so as to get its smell?
• Now light the incense stick. What happens? Do you get the smell sitting at a distance?
• Record your observations.

Activity 1.4

• Take two glasses/beakers filled with water.
• Put a drop of blue or red ink slowly and carefully along the sides of the first beaker and honey in the same way in the second beaker.
• Leave them undisturbed in your house or in a corner in the class.
• Record your observations.
• What do you observe immediately after adding the ink drop?
• What do you observe immediately after adding a drop of honey?
• How many hours or days does it take for the colour of ink to spread evenly throughout the water?

Activity 1.5

• Drop a crystal of copper sulphate or potassium permanganate into a glass of hot water and another into containing cold water. Do not stir the solution. Allow the crystals to settle at the bottom.
• What do you observe just above the solid crystal in the glass?
• What happens as time passes?
• What does this suggest about the particles of solid and liquid?
• Does the rate of mixing change with temperature? Why and how?

From the above three activities (1.3, 1.4 and 1.5), we can conclude the following:

Particles of matter are continuously moving, that is, they possess what we call the kinetic energy. As the temperature rises, particles move faster. So, we can say that with increase in temperature the kinetic energy of the particles also increases.

In the above three activities we observe that particles of matter intermix on their own with each other. They do so by getting into the spaces between the particles. This intermixing of particles of two different types of matter on their own is called 'diffusion'. We also observe that on heating, diffusion becomes faster. Why does this happen?

1.2.3 PARTICLES OF MATTER ATTRACT EACH OTHER

Activity 1.6

• Play this game in the field - make four groups and form human chains as suggested:
• The first group should hold each other from the back and lock arms like Bihu dancers (Figure 1.3).
  Figure 1.3

  

• The second group should hold hands to form a human chain.
• The third group should form a chain by touching each other with only their finger tips.
• Now, the fourth group of students should run around and try to break the three human chains one by one into as many small groups as possible.
• Which group was the easiest to break and why?
• If we consider each student as a particle of matter, then in which group the particles are held each other with the maximum force?

Activity 1.7

• Take an iron nail, a piece of chalk and a rubber band.
• Try breaking them by hammering, cutting or stretching.
• In which of the above three substances do you think the particles are held together with greater force?

Activity 1.8

• Open a water tap, try breaking the stream of water with your fingers.
• Were you able to cut the stream of water?
• What could be the reason behind the stream of water remaining together?

The above three activities (1.6, 1.7 and 1.8) suggest that particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another.

Questions 1.1

For the sake of convenience the answer to each question is given just below the question itself. Here Q denotes the question and A represents the corresponding answer.

Q1. Which of the following are matter?
(a) Chair
(b) Air
(c) Love
(d) Smell
(e) Hate
(f) Almonds
(g) Thought
(h) Cold
(i) Cold drink
(j) Smell of perfume

A1.
(a) matter
(b) matter
(c) not a matter
(d) not a matter
(e) not a matter
(f) matter
(g) not a matter
(h) not a matter
(i) matter
(j) matter

Q2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several metre away, but to get the smell from cold food you have to go close.

A2. As the kinetic energy of any matter rises with an increase in temperature, the particles move faster. This makes the smell of the hot sizzling food to reach us when we stand at a certain distance. While, as the temperature of the cold food is low, its kinetic energy of the matter is also less. This makes the smell particles to move very slowly or stay still which is why we need to go near the food item to get its smell.

Q3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

A3. Particles of matter have spaces between them, and the molecules of water are loosely bound to each other.

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

A4. Some characteristics of particles of matter are :
1. aarticles of matter are very small.
2. They are continuously moving.
3. Particles of matter have spaces between them.
4. Particles of matter attract each other.