# NCERT Class 9 Science Solutions: Chapter 1 Matter in Our Surroundings Part 1

Question 1:

Q. Which of the following are matter?

Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.

A. Anything that occupies space and has mass is called matter. Matter can exist in three physical states-solid, liquid, and gaseous.

Chair and almond are forms of matter in the solid state.

Cold drink is a liquid state of matter.

Air and small of perfume are gaseous states of matter.

Note: The sense of small is not matter. However, the smell or odour of a substance is classified as matter. The smell of any substance (say, perfume) is the gaseous form of that substance which our olfactory system can detect (even at very low concentrations). Hence smell of perfume is matter.

Question 2:

Q. Give reasons for the following observation:

The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.

A. Solids diffuse at a very slow rate. But, if the temperature of the solid is increased, then the rate of diffusion of the solid particles into air increases. This is due to an increase in the kinetic energy of solid particles. Hence, the smell of hot sizzling food reaches us even at a distance, but to get the smell from cold food we have to go close.

Question 3:

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

A. The ability of a driver to cut through water in swimming pool shows that matter is made up of particles.

Question 4:

What are the characteristics of particles of matter?

A. The characteristics of particles of matter are:

1. Particles of matter have spaces between them.

2. Particles of matter are continuously moving.

3. Particles of mater attract each other.

EXERCISE

Question 1:

The mass per unit volume of a substance is called density=mass/volume). Arrange the following in order of increasing density- air, exhaust from chimney, honey, water, chalk, cotton, and iron.

A. The given substances in the increasing order of their densities can be represented as:

Air < Exhaust from chimney < Cotton < Water < Honey < Chalk < Iron

Question 2:

(a) Tabulate the differences in the characteristics of states of matter.

A. The differences in the characteristics of states of matter are given in the following table.

 S. No. Solid state Liquid state Gaseous state 1. Definite shape and volume. No definite shape. Liquids attain the shape of the vessel in which they are kept. Gases have neither a definite shape nor a definite volume. 2. Incompressible Compressible to a small extent. Highly compressible. 3. There is little space between the particles of a solid These particles have a greater space between them. The space between gas particles is the greatest. 4. These particles attract each other very strongly. The force of attraction between liquid particles is less than solid particles. The force of attraction is least between gaseous particles. 5. Particles of solid cannot move freely. These particles move freely. Gaseous particles are in a continuous, random motion.

(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.

A. Rigidity can be expressed as the tendency of matter to resist a change in shape. Compressibility is the ability to be reduced to a lower volume when force is applied.

Fluidity is the ability to flow.

By filing a gas container we mean the attainment of shape of the container by gas.

Shape defines a definite boundary.

Kinetic energy is the energy possessed by a particle due to its motion.

Density is mass per unit volume.