Page 65 - Physics

Introduction to force

4. Stretch the coil spring until it extends
A force can therefore be defi ned as a push in length.
or pull experienced by an object. It is
usually described in terms of its magnitude Question
and direction. The SI unit of force is In each case, what action makes an
newton, N. One newton is the amount of object change its shape or direction?
force required to give a mass of one
kilogramme (1 kg) an acceleration of To move the carton of books, there is a
2
1 m/s . Therefore,1 N = 1 kg × 1m/s . need to either pull or push it. This means
2
that a force has to be applied. The rubber
Eff ects of forces band is pulled to stretch it while the spring
An object is stationary when all forces is pushed to compress it. These activities
demonstrate that pulling or pushing requires
acting on it are balanced. If a new force is a force.
applied to the object, the forces become
unbalanced. The result of unbalanced Determination of the magnitude of a
forces on an object can cause various
effects including: force
(a) change in the state of motion of an A spring balance can be used to estimate
the magnitude of force. It consists of a
object; coiled spring fi xed to a support at one end,
(b) change in the way the object moves; with a hook at the other end as shown in

(c) change of shape or size of the object; Figure 3.2 (a).
and

(d) change of direction in which an
object is moving. Rigid support

Acti vity 3.1
Aim: To demonstrate the Pointer Calibrated
effects of forces. scale

Materials: Carton of books, rubber
bands, table and coil spring
Procedure
1. Move the carton of books from one
end of the class to another without
lifting it.
2. Stretch a rubber band until it is close
to its breaking point.
3. Compress a coil spring between your Hook
hands. Figure 3.2: A spring balance

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