Page 63 - Innovator's Science-8

Run the comb through your hair again. This time hold it near a thin
stream of water from a tap. The streaming water will move towards the

comb. Electrostatic force is useful in controlling pollution by separating
solid pollutant particles from the smoke given out from factories.
Let us know where else in your daily life you can experience the
Comb a rac ng
bits of paper presence of electrostatic force.

• You might have noticed that when your mother empties a polypack of

pulses into a container, some of the pulse gains get stuck to the
polythene and do not fall in the container. This is because when the
grains slip out from the polypack, they get rubbed and charged. Both,
the grains and the polythene are stuck together due to the attraction
Comb a racts
tap water between the opposite charges.
• If you stand near the screen of the working television with synthetic

clothes on you, the clothes are attracted by the television screen. This
is because a working television screen is negatively charged. The
negative charge of the screen attracts the neutral clothes towards it.

Objects having no charge on them are called neutral. A charged object,
either negative or positive, attracts other neutral objects.

SPRING BALANCE
Spring Balance
Spring balance is a device that measures force. It uses the principle that
Science greater the force, the greater is extension that force produces on a coiled
Bytes
spring. It consists of a coiled spring with a pointer attached to it. As the
Testimony spring is stretched, the pointer moves on a graduated scale. The reading
The spring balance was
first invented by Richard on the scale gives the magnitude of the force.
Salter in 1770 to weigh
trade goods accurately. WEIGHT AND ITS MEASUREMENT
The force with which the Earth pulls an object towards itself is called the
weight of the object. The weight measures how strongly an object is
pulled by the Earth. Since the weight is a force, it is measured in the

same unit as that of force. Therefore, Sl unit of weight is also newton (N) .
Let us now try to find out if the Earth pulls every object with equal force.

• Take a spring and a few objects of different masses, such as a pencil
box, a tiffin box, and a small stone. Hang one end of the spring from a
nail. From the other end, hang an object and observe the spring.

Does the spring stretch?
• Now hang the other objects, one by one and notice the stretch in the

spring each time. Is the stretch caused by each object the same?

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Science-8