NCERT SOLUTION FOR SCIENCE 9TH STANDARD.
CHAPTER 1: Matter in Our Surroundings.
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.
Solution
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 is a gaseous state of matter.
Notes
Note: The sense of smell is not matter. However, the smell or odour of a substance is classified as matter. The smell of any substance (say, perfume) can be classified as matter. This is because, perfume is in liquid state inside the bottle. It comes out in the form of tiny droplets. These droplets of perfume are matter and spread out in the atmosphere to create a sense of smell. This smell can be detected by our olfactory system.
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.
Solution
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.
A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Solution
The ability of a diver to cut through water in a swimming pool shows that the particles of matter have intermolecular spaces. The intermolecular spaces in liquids is fair enough to let the diver pass through it.
What are the characteristics of particles of matter?
Solution
The characteristics of particles of matter are:-
(i) Particles of matter have spaces between them.
(ii) Particles of matter are continuously moving.
(iii) Particles of mater attract each other.
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.
Solution
The given substances in the increasing order of their densities can be represented as:
Air < Exhaust from chimney < Cotton < Water < Honey < Chalk < Iron
Tabulate the differences in the characteristics of states of matter.
Solution
Comment upon the following:-
Rigidity
Solution
The rigidity can be expressed as the tendency of matter to resist a change in shape.
Compressibility
Solution
Compressibility is the ability to be reduced to a lower volume when force is applied.
Fluidity
Solution
Fluidity is the ability to flow.
Filling a gas container
Solution
By filling a gas container we mean the attainment of the shape of the container by gas.
Shape
Solution
The shape defines a definite boundary.
Kinetic energy
Solution
Kinetic energy is the energy possessed by a particle due to its motion.
Density
Solution
Density is mass per unit volume.
Comment upon the following:- rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.
Solution
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 filling 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.
Give reasons:- A gas fills completely the vessel in which it is kept.
Solution 1
There is little attraction between particles of gas. Thus, gas particles movefreely in all directions. Therefore, gas completely fills the vessel in which it is kept.
Solution 2
The molecules of gas have high kinetic energy due to which they keep moving in all directions and hence fill the vessel completely in which they are kept.
A gas exerts pressure on the walls of the container.
Solution 1
Particles of gas move randomly in all directions at high speed. As a result, theparticles hit each other and also hit the walls of the container with a force. Therefore, gas exerts pressure on the walls of the container.
Solution 2
A gas exerts pressure on the walls of the container because the molecules of the gas are in constant random motion due to high kinetic energy. These molecules constantly vibrate, move and hit the walls of the container thereby exerting pressure on it.
