Some Natural Phenomena | Science Grade 8 CBSE

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The six ideas behind these phenomena

From a charged comb to a lightning bolt, and from slipping plates to staying safe — these six terms tie together two of nature's most dramatic events. Tap each one to find out what it means.

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The three big ideas

Rubbing two objects can transfer charge from one to the other. There are two kinds of charge — positive (+) and negative (−).
Like charges repel; unlike charges attract. Two objects with the same charge push apart; opposite charges pull together.
Everyday examples: a comb rubbed on dry hair lifts bits of paper; a balloon rubbed on wool sticks to a wall; a plastic rod rubbed with a woollen cloth picks up charge.
This stored charge is called static electricity. It can be transferred by touch, and a device called an electroscope can detect whether an object is charged. Letting the charge flow away into the ground is called earthing.

Worked example. Why does a charged balloon stick to a wall, even though the wall is not charged?

The charged balloon pulls the opposite charges in the wall slightly closer to its surface. The attraction between the balloon and these induced charges is enough to hold it in place.

Common mistake: assuming that if an object is attracted, it must be charged. A charged object can attract an uncharged one too (by inducing opposite charges) — so attraction alone does not prove a charge.

In a storm cloud, moving air and water droplets separate the charges — lighter positive charges gather near the top, heavier negative charges near the bottom.
When the charge grows large enough, the air breaks down and a huge spark (electric discharge) jumps between clouds or from cloud to ground — that flash is lightning. The rapid heating of the air makes the sound of thunder.
The famous kite experiment by Benjamin Franklin showed that lightning is the same kind of electricity as the spark you feel from rubbing.
A lightning conductor is a metal rod fixed on tall buildings and joined by a thick wire to a metal plate buried in the ground; it carries the charge safely to the earth.
Safety rules: go indoors; avoid open fields, hilltops and lone tall trees; do not bathe or touch metal taps and pipes; avoid wired phones and electronics; if caught outside with no shelter, crouch low with feet together and head tucked — do not lie flat.

Worked example. You are caught in an open field when a thunderstorm begins, with one tall tree nearby. What should you do?

Do not shelter under the tree — it is the tallest object and likely to be struck. Crouch low on the ground with your feet together, making yourself as small as possible, until you can reach a building.

Common mistake: sheltering under a lone tall tree or staying in the open. These are the most dangerous spots in a thunderstorm — a strong building is far safer.

The Earth's crust is made of large moving plates. Their boundaries are weak zones (faults). When stress builds up and the rock suddenly slips, the released energy shakes the ground — an earthquake.
The point underground where it starts is the focus; the point on the surface directly above is the epicentre. The energy spreads out as seismic waves.
A seismograph records the waves, and the strength (magnitude) is given on the Richter scale. Quakes above magnitude 5 can cause damage; those above 7 are highly destructive.
India's earthquake-prone zones include Kashmir and the whole Himalayan belt, the Indo-Gangetic plain, the Northeast, Kutch in Gujarat and parts of Rajasthan.
Protection: build earthquake-resistant houses (lighter roofs, flexible frames) in high-risk zones; fix shelves and heavy objects to walls; keep an emergency kit. During shaking — drop, take cover under a sturdy table, and hold on; stay away from windows; if outdoors, move to open ground away from buildings, trees and power lines.

Worked example. The shaking starts while you are indoors. What is the safest immediate action?

Get under a strong table and hold on, away from windows and heavy furniture. Running outside during the shaking is risky because of falling objects.

Common mistake: believing earthquakes can be predicted to the day. They cannot — so preparation and earthquake-resistant buildings matter far more than trying to forecast the exact moment.

Where you'll meet it

These forces in real life

Lightning rods on tall buildings

Temples, towers and high-rise flats carry a metal rod connected to the earth, so a lightning strike is led harmlessly to the ground instead of damaging the building.

Earthquake-safe houses

In the Himalayan and Kutch regions, homes are built with lighter roofs and flexible frames so they sway rather than collapse when the ground shakes.

The crackle of a woollen sweater

Pulling off a woollen sweater in dry weather makes tiny sparks and crackles — the very same kind of electric charge as lightning, only on a miniature scale.

Check yourself

Competency quiz

Modelled on the competency-based pattern — MCQ, assertion–reason and a case study, testing whether you can use the ideas, not just recall them.

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