NCERT Book Class 9 Science (Exploration) Chapter 6 How Forces Affect Motion

Chapter
How Forces Affect
6 Motion

Think It Over In Chapter 4, you learnt to describe the motion of an object in terms
of its position, velocity and acceleration. But you did not consider
y Why does a canoe what causes motion. Is there an underlying cause for a change in
move forward position and velocity of an object? What is the nature of this cause?
when the canoeist Do all motions require a cause? In this chapter, we will investigate
pushes water
what causes changes in the motion of objects. We will also discuss
backwards with
their paddle and
Newton’s three laws of motion and learn how to apply them.
why does it move
faster when they 6.1 The Concept of Force
push harder? You may recall learning earlier that a force can make an
Grade 8
y Suppose the same object move from rest, change the speed and direction
Curiosity
Chapter 5
canoeist uses the of motion of a moving object, and can even change the
same paddle force shape of an object. For example, a ball at rest starts moving when
in two different
you apply a force, a force applied by a cricket bat on a cricket ball
canoes, one empty
and one carrying
changes its direction, and a lemon can be squeezed by the force
another passenger. applied by your fingers (Fig. 6.1).
In which case will
the canoe move
faster?

(a) Kicking a ball (b) Striking a ball (c) Squeezing a lemon
Fig. 6.1: Applying force on different objects