NCERT Book Class 9 Science (Exploration) Chapter 7 Work, Energy, and Simple Machines

Chapter
Work, Energy, and
7 Simple Machines

In earlier Chapters 4 and 6, you have learnt how forces change the
motion of objects, and how kinematic equations and Newton’s laws can
Think It Over be used to analyse motion. But when forces change with time or act in
complicated ways, applying these laws directly can become difficult. Is
y What will be there a simpler and more powerful way to understand such situations?
the magnitude
of velocity of In this chapter, you will explore the ideas of work, energy and power,
the child at the which often allow us to analyse motion and interactions more easily. You
bottom of the will also learn about simple machines, which help us perform tasks with
blue slide? less effort and more convenience. These form the building blocks of many
y Will two everyday machines. Energy, which is the capacity to do work, lies at the heart
children of of all these ideas and of almost every activity in our daily life (Fig. 7.1).
different masses
reach the bottom
of the same slide
with the same
velocity?
y Which of the Food provides Electricity provides Fuel provides energy to
slides will result energy to walk energy to rotate a fan move a car
in the largest Fig. 7.1: Energy required to carry out tasks comes from various sources
magnitude of
velocity for We often use the words work, energy, and power in everyday
the child at its conversations. As we learnt in Chapter 1, these terms have a precise
bottom? meaning in science. Let us first understand how to define work.