NCERT Science Class 9: Gases, Liquids and Solids

NCERT Science Class 9

In class nine, you will learn about the properties of liquids and gases. You will also learn about phase changes and the solid-liquid-gas system in ncert solutions for class 9 science.

One of the essential things about gases, liquids and solids is their behaviour in different environments. In this science class, we will discuss the behaviour of gases, liquids, and solids in different settings.

Gases behave differently in different environments. For example, gas molecules are much smaller than liquid molecules, so they move around more easily. This is why gas molecules travel up a balloon and escape quickly.

Liquids behave differently in different environments. For example, a liquid can absorb gas molecules from the atmosphere. This is why a bottle of water will take in carbon dioxide from the air.

Solids also behave differently in different environments. For example, a solid can be crushed into small pieces by pressure or heat. This is why you can’t put ice cream in the freezer too long or it will turn into a liquid.

Pressure in Liquids

One of the key properties of liquids is that they have a higher pressure than gases. This is because liquids are made up of tiny particles that are held together by forces called molecular forces. Gases, on the other hand, are composed of large particles that are not held together as tightly.

The pressure inside a liquid is determined by the number of molecules in the liquid. More molecules mean more pressure. Liquids with a low number of molecules have low pressure, while liquids with a high number of molecules have high pressure.

Liquids can be divided into two categories based on their pressure: low-pressure and high-pressure. Low-pressure liquids have a pressure below 14.7 pounds per square inch (psi), while high-pressure liquids have pressure above 14.7 psi.

One way to measure the pressure inside a liquid is with a barometer. A barometer measures the air pressure outside and converts it to an estimate of the liquid’s pressure. Infinity Learn provides the best online study guide for cbse solutions for class 9 science.

Pressure In Gases

One of the most important properties of gases is their pressure. Pressure is a force that opposes the flow of gas molecules. When gas molecules move through a container, they experience the pressure of the container.

The pressure of a gas depends on three factors: the volume of the gas, the temperature of the gas, and the pressure inside the container. The more gas molecules there are, the higher its pressure will be. The temperature of a gas also affects its pressure. Warm gases have higher pressures than cold gases. And, finally, gas molecules in a closed container have a higher pressure than those in an open container.

Gases can be divided into two categories based on their pressure: low-pressure gases and high-pressure gases. Low-pressure gases have lower pressures than high-pressure gases. For example, air has low pressure (about 14 millibars), while water has a high pressure (about one bar).

Different Densities

One of the important properties of gases, liquids, and solids is their density. Gases, liquids, and solids have different densities because of the amount of matter (or substance) that they contain.

Gases have the lowest density because they have a large amount of empty space inside them. Liquids have a middle density, which is between that of a gas and a solid. Solids have the highest density because they have a lot of matter in small spaces.

Density is important for many reasons. For example, it affects how liquids flow through pipes and how gases move through the air. It also affects how heat moves through substances.

Diffusion And Osmosis

Diffusion is the movement of a substance from an area of high concentration to an area of low concentration. Osmosis is the diffusion of water through a semipermeable membrane.

Gases, liquids, and solids can all be diffused through a semipermeable membrane. Gases diffuse through the membrane in all directions, while liquids and solids diffuse in only one direction. This process is called diffusion.

Diffusion occurs when a gas (like air) moves from areas with high concentration (like the atmosphere) to an area with low concentration (like your lungs). The gas molecules move through the air so quickly that they can’t stop and form clouds. This is why we sometimes see foggy conditions: The air contains a lot of vapor, which is made up of tiny gas molecules.

Osmosis happens when water moves from an area with high water content to an area with low water content. The goal of osmosis is to equalize the water levels in two different places. This process is important for example when you take a bath: The water moves from your bathtub to your body because the cells in your skin are able to transport water across the barrier that separates them.


Gases, liquids, and solids are all substances that can be found in the world around us. In this lesson, we have looked at how these substances behave under different conditions and how they can be used to solve problems. We have also seen how each type of substance interacts with other substances. Finally, we have explored some examples of where gases, liquids, and solids can be found in everyday life. I hope you have enjoyed this introductory lesson on gases, liquids, and solids!