Chapter 1: Matter in Our Surroundings- Exercise- 2

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Chapter 1: Matter in Our Surroundings

Class: IX

Exercise 2

Question 1

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

Answer 1

The given substances in the increasing order of their densities,

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

Question 2

a) Tabulate the differences in the characteristics of states of matter.
b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.

Answer 2

a) The differences in the characteristics of states of matter are given below.

ncert science class 9 chapter 1

b) Rigidity is the ability of a substance to retain its shape when the force is applied.

Compressibility is the ability of matter to get reduced to a lower volume when a force or pressure is applied.

Fluidity is the ability of a substance to flow.

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

Shape is defined a definite boundary or physical appearance of something.

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

Density is the mass per unit volume.

Question 3

Give reasons

a) A gas fills completely the vessel in which it is kept.
b) A gas exerts pressure on the walls of the container.
c) A wooden table should be called a solid.
d) We can easily move our hand in air, but to do the same through a solid block of wood, we need a karate expert.

Answer 3

a) Attraction between particles of gas is less. Thus the gas particles can move freely in all Therefore, gas completely fills the vessel in which it is kept.
b) Gas particles move in all directions at high-speed. As a result, these gas particles hit with each other and against the walls of the container with a force. Therefore, gas exerts pressure on the walls of the container.
c) A wooden table has a definite shape and volume and it is very rigid. So, it can't be compressed. These are the characteristics of a solid and hence, we can say that wooden table is a solid.
d) Particles of air have large spaces between them and the wood has only little space between its particles. Also, the wood is rigid. That’s why we can easily move our hands in air, but to do the same through a solid block of wood, we need a karate expert.

Question 4

Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Answer 4

Density is mass per unit volume of a substance (density = mass/volume).

The density of a substance decreases as its volume increases.

Ice has large number of empty spaces between its particles and these spaces are larger as compared to the spaces present between the particles of water. Thus, the volume of ice is greater than that of water and therefore the density of ice is less than that of water. A substance with lower density than water can float on water and that is why, ice floats on water.

Chapter 1: Matter in Our Surroundings- Exercise- 2

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