Let’s explore a concept from everyday life: proportionality! If a change in one physical phenomenon creates a predictable change in another phenomenon, they are related. The change happens proportionally, either in the same direction or opposite directions. Learn more about this in NCERT Maths Chapter 13 – Direct and Inverse Proportions.
Topics Covered in Chapter 13 – Direct and Inverse Proportions
Introduction 

Direct Proportion 

Inverse Proportion 

NCERT Solutions 
The physical world is run by scientific laws and phenomena. There are ample examples of proportions in physics and chemistry. For instance, sound is a wave that travels through air. That’s why we can hear sounds. As the temperature increases, sound waves travel faster than usual. This is because the air gets lighter during the summer, and its density decreases. Conversely, as the temperature decreases, sound waves travel slower than usual. This is because the air gets heavier in colder seasons, and its density increases.
Against this background, many questions arise: what is the relationship between the speed of sound and the temperature of air? What is the relationship between the speed of sound and the density of air? Finally, how does temperature change affect the density of air?
In the natural world, phenomena like speed, time, heat level, and air density are all examples of quantities. In science, a quantity is measurable on a specific scale made for it. Weight can be measured in grams or pounds; time is measured in milliseconds, minutes, hours, and even years, decades, and centuries; and heat is measured in Celsius or Fahrenheit.
These are the kinds of questions that help further explore direct and inverse proportions.
The learning app MSVgo explores such concepts in detail, simply and vividly. Let’s study the class 8 concept of direct and inverse proportions in depth.