Class 9 Science Short Notes 2026-27

1.1 WHAT IS SCIENCE?

In your earlier classes, you have explored a number of phenomena around you. You observed plants and animals, asked questions about why things happen the way they do, and performed simple activities to find answers. As you enter secondary school, the study of science becomes deeper. It is not only about learning what happens, but also about understanding how and why it happens, and about the methods that scientists use to arrive at reliable knowledge.

Science is not just a collection of facts and formulae. It is a way of understanding the world around us, based on careful observation, questioning, making a guess or hypothesis, and testing it through experiments. The results of experiments may support the hypothesis, or they may require it to be changed. In this sense, scientific knowledge is always open to revision when new evidence becomes available.

The natural world is very complicated, so scientists often use models to simplify it. A model focuses only on the important details and deliberately ignores the less important ones. In science, many common words such as force, work, reaction and cell have special meanings, and quantities are expressed with symbols and units so that there is no confusion.