9th science

# Matter In Our Surroundings

## Solution of NCERT In Text Questions-Part-1

Question 1: Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.

Answer: Chair, air, almonds, and cold-drink are matters.

Explanation: Things that occupy space and have some mass are called matter. Since chair, air, almonds and cold-drink occupy some space and have some mass, so these are matter.

Question 2: Give reasons for the following observation: The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.

Answer: Smell of anything comes because of gases emanating from the given thing. The smell reaches to us because of diffusion of gas. The rate of diffusion increases with increase in temperature. This happens because of higher kinetic energy due to higher temperature. That is why smell of hot sizzling food reaches to us from several feet. On the other hand, the kinetic energy of gases emanating from cold food is low because of lower temperature. Due to this, we need to move closer to a cold food to take its smell.

Question 3: A diver is able to cut through water in a swimming pool. Which property of mater does this observation show?

Answer: Water is also a matter. We know that particles of matter have space between them. In case of fluids, the space between particles is large enough and due to this it becomes easier for a diver to cut through water in a swimming pool.

Question 4: What are the characteristics of the particles of matter?

Answer: Characteristics of the particles of matter:

• The particles of matter are very small.
• The particles of matter have space between them.
• The particles of matter are moving constantly.
• The particles of matter attract one another.

Question 5: 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 chimneys, honey, water, chalk, cotton and iron.

Answer: Air < Exhaust from chimneys < cotton < Water < Honey < Chalk < Iron

Explanation: Air is the mixture of gases. Chimney exhaust is also a mixture of gases; along with some heavier particles, such as ash. This makes the density of chimney exhaust more than air.

Cotton is a porous solid and which has lot of air trapped within pores. This makes its volume more than water. Therefore, it is less dense than water.

Question 6: (a) Tabulate the differences in the characteristics of states of matter.

SolidLiquidGas
Definite shapeIndefinite shapeIndefinite shape
Definite volumeDefinite volumeIndefinite volume
Maximum force of attraction between particlesLess force of attraction between particlesNegligible force of attraction between particles
Particles are closely packedParticles are loosely packedParticles are highly loosely packed
Cannot be compressedCan be compressed to some extentCan be compressed to a large extent
Kinetic energy of particles is minimumKinetic energy of particles is mediumKinetic energy of particles is very high
Particles cannot move rather vibrate one over anotherParticles can slide one over anotherParticles can move freely
Highest densityModerate densityLeast density
Cannot flowCan flowCan flow

Question 7: (b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density

Answer: Rigidity: The greatest force of attraction between particles and close packing of particles make solids rigid. Rigidity is one of the unique properties of solids. Because of rigidity, a solid can resist from getting distorted. Because of rigidity a solid has definite shape and volume. Rigidity is negligible in fluid and gas.

Compressibility: Compressibility is one of the most important characteristics of gas. Because of lot of space between particles, a gas can be compressed to a great extent.

Liquid and solid cannot be compressed because of the least space between their particles.

Fluidity: The ability to flow is called fluidity. The less force of attraction and more space between particles make liquid and gas to flow. Thatâ€™s why liquid and gas are called fluid.

Filling of a gas container: Liquids do not fill a gas container completely, while gases fill the gas container completely in which it is kept. This is because the particles of gas can move in all the directions.

Shape: Solids have fixed shape. Liquid and gas take the shape of the container in which they are kept. This happens because of less force of attraction and more kinetic energy between particles of liquids and negligible force of attraction and highest kinetic energy between particles of gas.

Kinetic energy: The kinetic energy of particles of solid is the minimum. They only vibrate at their fixed position. The kinetic energy of particles of liquid is more than that of solid. But they can slide above one another. The kinetic energy of particles of gas is the maximum.

Density: The mass per unit volume of a substance is called density. The density of solid is highest, of liquid is less than solid and of gas is minimum.