Class 8 Science Chapter 6: Pressure, Winds, Storms and Cyclones

Two Bags, One Sore Shoulder

Megha and Pawan set off for a picnic carrying identical things in their bags. Within a few minutes Pawan is shifting his bag about and complaining that his shoulders hurt. Megha, carrying the same load, is perfectly comfortable. Both bags weigh the same. So what is going on?

What Differs

Pawan works it out himself: the straps. His bag hangs from narrow straps and hers from broad ones. That is the only difference between the two, and it turns out to be enough.

Why Area Comes Into It

The weight of a bag presses down on your shoulder because the Earth is pulling the bag down. With narrow straps that pull is concentrated on a small patch of shoulder. With broad straps the identical pull is shared out across a much wider patch. Each bit of shoulder carries less.

The Quantity

Since the area matters as much as the force, there is a quantity that puts the two together. Pressure is the force acting on each unit of area, so you find it by dividing the force by the area it acts over.

Perpendicular Only

One restriction at this stage. The force used in that division is the one acting at right angles to the surface. A force sliding along a surface is doing something else, and later grades take that up.

The Unit

Force is measured in newtons and area in square metres, so pressure comes out in newtons for every square metre. That combination has a name of its own, the pascal, written Pa. It is named after a person, so the symbol takes a capital letter.

A Worked Example

Take a force of 100 N pressing on a board of area 2 m2. Divide one by the other and the pressure is 50 N for each square metre, which is 50 Pa. Notice how ordinary the arithmetic is; the thinking is all in choosing the right area.

Broad Handles and Cloth Pads

Once you have the idea you start seeing it everywhere. A bucket of water is easier to carry by a broad handle than by a thin one. People carrying pots or baskets on their heads slip a ring of cloth underneath first. In every case the load is unchanged and the area it presses on has been made larger.

When You Want It Low

That is the first half of the subject: wherever a load has to rest on skin, or on soft ground, or on anything that might give way, spreading it out lowers the pressure and solves the problem.

When You Want It High

And the second half is the opposite. Sometimes high pressure is exactly what you are after, and the way to get it is to make the area as small as you can.

A Nail, Two Ways Round

Try driving a nail into wood head first. It does not go in. Turn it round and the same hammer blow drives the point straight in, because the whole force is now concentrated into a tiny area and the pressure there is enormous.

A Knife, Two Edges

A knife makes the same point. Press the blunt back of the blade onto an apple and nothing much happens. Use the sharp edge with the same push and it cuts through at once. The sharpness is not strength; it is a very small area.

The Rule in Both Directions

So the rule works both ways, and it is worth saying as one sentence. Shrink the area and the pressure from a given force goes up. Enlarge the area and the pressure goes down. Nothing about the force itself has to change in either case.

Where You Have Seen It

Think about a drawing pin, with a broad head for your thumb and a sharp point for the wall. One end is designed for low pressure and the other for high, on the same tiny object, with one force passing through both.

A Caution About Weight

Here is the mistake worth guarding against. A comfortable bag is not a lighter bag. Comfort tracks pressure, not weight, and the weight in Megha’s bag is exactly what is in Pawan’s. If you catch yourself saying something got lighter, check whether what really changed was the area.

What To Carry Forward

Pressure is force for each bit of area, measured in newtons per square metre, which is the pascal. The same force gives a high pressure on a small area and a low pressure on a large one. Broad straps, wide handles and cloth pads use the second; nails, knives and pins use the first.

Scenario:

On one morning in a market four people are carrying things. A schoolboy has a heavy bag on narrow straps and keeps shifting it. His sister carries the same books on broad straps and barely notices. A vegetable seller balances a basket on her head with a round pad of cloth beneath it. A water carrier has swapped his bucket for one with a wide handle. A pupil watching writes that the broad straps, the cloth pad and the wide handle all reduce the weight being carried, which is why all three people look comfortable.

Analysis:

Three of the four are solving the same problem in the same way, and the pupil has named the wrong quantity. Nothing in the market has become lighter. What each of the three has done is spread an unchanged force over a larger area, which lowers the pressure where it is felt.

Activity:

Carry the same bag on narrow and on broad straps for a minute each, and write down which shoulder notices.

Title:

Try it at home: the pencil test

Safety:

Gently, and never hard enough to break the skin. Stop at once if anything is uncomfortable.

What You Notice:

The order follows the area and not the force, because the push was the same every time. The sharp point concentrates it into the smallest patch, so the pressure there is highest.

A drawing pin carries both halves of this topic at once: a broad head so it does not hurt your thumb and a sharp point so it goes into the wall.

Sharpening a knife changes nothing about how strong it is; it only makes the edge press on a much smaller area.

A loaded cart that sinks into soft ground on narrow wheels rolls over the same ground on wide rims, carrying exactly the same load.

SAME FORCE, DIFFERENT AREA — Nothing about the push has to change. Shrink the area for more pressure and widen it for less.

COMFORT IS PRESSURE, NOT WEIGHT — A cloth pad or a broad strap never removes any weight. It changes the area the weight presses on.

Why Tanks Sit on Roofs

Look at the water tanks around where you live. Almost all of them are up on a roof or on a tower. Somebody had to lift all that water up there, so there must be a reason for the trouble. Keep the question in mind; this topic answers it.

Two Pipes, Two Widths

Here is the experiment that settles it. Take two clear pipes of about the same length, one narrow and one broad, and fasten a good rubber balloon over the lower end of each. Clamp both upright on a stand side by side.

Fill Them to One Level

Now pour water into both until the surface sits at the same height in each, about halfway up. The broad pipe obviously holds a great deal more water than the narrow one, so it is heavier by a long way.

Both Balloons, One Bulge

Look at the two balloons. They bulge by the same amount. Not nearly the same: the same. The pipe with far more water in it is stretching its balloon no further than the thin one beside it.

Why That Is Surprising

That rules out the obvious explanation. If the weight of the water were doing the stretching, the broad pipe would win easily, because it carries much more of it. The weight of water in the pipe cannot be what the balloon is responding to.

So What Is Responsible

What the two pipes do have in common is the height of the water standing in them. It is the pressure of that column, rather than its weight, that pushes the balloon out, and the pressure turns out to follow the height.

Pour In More

Test it directly. Add more water to one of the pipes and the balloon on it swells further. Add more again and it swells more still. Each time the column gets taller the bulge grows with it.

Height Is the Thing

So the pressure a liquid exerts at the bottom of a vessel goes up as the height of the liquid above it goes up. Two vessels of quite different widths filled to one level give one pressure at the bottom.

And Not Only Downwards

A balloon on the bottom of a pipe only tests the downward push. Is that the only direction a liquid presses in? The next activity answers it, and the answer changes the picture.

Three Holes in a Bottle

Ask an adult to make three small holes down one side of a plastic bottle, evenly spaced from top to bottom. Cover all three with tape, stand the bottle in a tray and fill it with water to the brim.

Water Out of Every One

Now pull all three pieces of tape off together. Water jets out of every hole, sideways, away from the bottle. Nobody squeezed anything. The water inside was pressing outwards on the wall all along, and the tape was all that held it.

In Every Direction

So a liquid presses on the sides of its container as well as on the base. In fact it presses in every direction at once, which is why no part of a vessel holding water can be treated as safe from it.

A Leaking Pipe

You have seen this without naming it. A pipe with a hole in its joint sends water out in a jet, often across a street. Nothing is pushing that water out except the pressure of the water behind it against the wall of the pipe.

Why a Dam Is Broad Below

It explains something you may have wondered about in photographs. The base of a dam wall is far broader than its top. That is not only about holding up its own weight: the water presses horizontally on the wall, and that sideways pressure is largest near the bottom, where the column above is deepest. The broad base is built to withstand it.

Back to the Roof Tank

And it answers the question we started with. Pressure follows the height of the column, so putting the tank high gives every tap below it a useful pressure. A tank at ground level would leave the taps on the upper floors with very little.

What To Carry Forward

A liquid exerts pressure, and that pressure depends on the height of the column above the point you are asking about rather than on how much liquid there is. It presses on the sides as well as the base, and in every direction. Roof tanks, spurting leaks and broad-based dams are all the same fact seen from different angles.

Scenario:

A class clamps a narrow pipe and a broad pipe side by side. They fit a balloon to the lower end of each and fill both with water to the same level. Both balloons bulge by the same amount. One group writes that the broad pipe must be leaking, since it holds much more water and should bulge further. Another pours extra water into the narrow pipe, sees its balloon swell more, and concludes that narrow pipes give more pressure. A third group tapes three holes down a bottle and asks what will happen when the tape comes off.

Analysis:

The first group has assumed the answer and then explained away the result. The second has changed two things at once, the height and nothing else, and drawn a conclusion about width from it. The third group is about to find out that the sides of a container feel the pressure too.

Activity:

Fill a taped bottle with water, remove the tape and note which hole throws water furthest.

Title:

Try it at home: three holes, three jets

Safety:

An adult makes the holes. Do this over a sink or a tray, and keep water away from anything electrical.

What You Notice:

All three throw water sideways, which shows a liquid presses on the walls as well as the base. The lowest jet reaches furthest, because it has the tallest column of water above it.

A broad pipe holding far more water stretches its balloon no further than a narrow one filled to the same level, which is what rules the weight of the water out.

The lowest of three holes down a bottle throws water furthest, because it carries the tallest column of water above it.

A dam wall is broad at the foot partly to withstand a horizontal push from the water that is largest near the bottom.

HEIGHT, NOT HOW MUCH — A thin tall tube beats a wide shallow tank. The depth above the point is what counts.

EVERY DIRECTION — Base, sides and all ways at once. The holes in the bottle are the proof.

Air Is All Around

Liquids press on whatever holds them, as the last topic showed. Air is a good deal less obvious. It is everywhere, you cannot see it, and most of the time you do not notice it at all. Does it press on things too?

The Atmosphere

The air wrapped round the Earth has a name: the atmosphere. It is not a thin skin either. It reaches many kilometres upwards from the ground, which means there is a great depth of it above your head at this moment.

What Is In It

It is a mixture. Nitrogen and oxygen make up most of it, with argon and carbon dioxide present as well, and several other gases in small amounts. Nothing in this topic turns on which gas is which; what matters is that there is a lot of it.

Does It Press?

Here is how to find out, and the design is clever because it changes only one thing. Turn a paper plate upside down and fix a stick to the middle of it so you have something to lift it by. Stand it on a flat surface.

Folded First

Take a large sheet of chart paper, fold it twice into a small thick square and make a hole for the stick. Lay it over the inverted plate and lift the whole thing by the stick. It comes up easily.

Then Unfolded

Now take an identical sheet, leave it completely unfolded, make a hole in the middle and lay it flat over the plate. Lift again. This time it is noticeably harder.

Same Sheet, More Effort

Stop and notice what has and has not changed. The sheets are identical, so the weight you are lifting is the same. What changed is the area: unfolded, the sheet covers far more of the surface than the small folded square did.

What That Means

More area, more effort. Something must be pushing down on that sheet, and the total push grows as the area grows. Since the only thing resting on the sheet is air, the air must be pressing on it.

Atmospheric Pressure

That push has a name. The pressure the air around us exerts is called atmospheric pressure, and it acts on everything, not only on sheets of chart paper in an experiment.

In Every Direction

Does it act downwards only? Blow up a balloon and watch what happens. It swells in every direction at once, because the air inside is pressing outwards all over the skin. Air, like a liquid, presses in all directions.

The Sucker

Now for the size of it. Press a rubber sucker firmly against a smooth flat surface and it stays. Try to pull it straight off and you will find it surprisingly difficult. Nothing is glued and nothing is hooked.

Why It Holds On

Pressing it squeezes most of the air out from under the cup, so the pressure in there drops. The ordinary air outside is now at a higher pressure than the air inside, and that difference holds the cup against the surface. To get it off you have to overcome that difference.

How Large Is It?

The chapter gives one figure to make the scale real. Take a patch of about fifteen centimetres each way. The air column standing above a patch that size presses down with a force of roughly two thousand two hundred and fifty newtons, which is what the Earth would pull on a mass of about two hundred and twenty-five kilograms.

Why We Are Not Crushed

That raises an obvious worry. Why does a force like that not flatten us? Because the pressure inside your body is about the same as the pressure outside it, so the two balance. The fluids and gases moving through your tissues and organs are what keep the inside pressure up.

Millibars and Hectopascals

One last matter of units. The SI unit is still the pascal, but weather reports use a more convenient size. A millibar is a hundred pascals, and so is a hectopascal, which is why you will see both on a weather chart.

Back to the Plate

It is worth going back to the paper plate once more, because it is the ' cleanest piece of reasoning in the topic. Two sheets, identical in every respect but how they were folded, and a difference in effort that only an invisible push on the larger area can explain.

What To Carry Forward

Air presses on everything, in every direction, and that push is called atmospheric pressure. It is large, as a sucker and the plate experiment both show, and we survive it because our insides push back just as hard. The next topic asks what happens when the pressure is not the same everywhere.

Scenario:

A group runs two demonstrations. First they stand an upturned paper plate with a stick through it and cover it with a chart sheet folded twice, lifting it easily by the stick. Then they unfold the same sheet, lay it flat over the plate and find it far harder to lift. Next they press a rubber sucker against a window and nobody can pull it off. A pupil writes that the unfolded sheet was heavier and that the sucker must have glue on it, since nothing else was touching either of them.

Analysis:

Both demonstrations turn on the same invisible push. The pupil has reached for a visible explanation in each case. The sheet is the stronger evidence. It is the identical sheet in both halves of the test, and only its area changed.

Activity:

Press a sucker onto a smooth surface, try to pull it off, then lift one edge to let air in and try again.

Title:

Try it at home: the stubborn sucker

Safety:

Pull straight and steadily rather than jerking, and keep clear of glass edges. Ask an adult if the surface is a window.

What You Notice:

Letting air in raises the pressure under the cup until it matches the pressure outside, and the sucker comes away at once. Nothing about the rubber changed, only the pressure difference across it.

The air column above a patch about fifteen centimetres each way presses down with roughly the force the Earth would exert on a couple of hundred kilograms.

A sucker comes away at once if you lift one edge of the rim, because that lets air in and the pressures level out.

A millibar and a hectopascal are the same size, which is why a weather chart may use either of them.

SAME SHEET, MORE AREA — The weight never changed between the two lifts. Only the area the air could press on did.

A DIFFERENCE, NOT A GLUE — A sucker is held by lower pressure inside than out. Let air in and it drops.

Some Days It Blows

On some days the wind is strong enough to be a nuisance, and on others the air is perfectly still. Sometimes it is strong enough to damage houses and hurt people. The last topic established that air presses on everything. This one asks what happens when it does not press equally everywhere.

Two Clues You Have Already Seen

Leave an inflated balloon untied and the air rushes out of it. Puncture a bicycle tube and the air leaves there too, and the tube collapses. In both cases air inside at a high pressure finds its way out to where the pressure is lower.

Two Balloons and a Straw

Here is the experiment that makes it exact. Push one end of a drinking straw into a limp, uninflated balloon and tie it on so no air can leak. Inflate a second balloon, hold its neck closed, and tie that over the free end of the straw. Now you have a full balloon joined to an empty one.

Predict, Then Watch

Before you let go, say what you expect. Then release the neck and watch. Air crosses from the inflated balloon into the empty one. The full one shrinks and the limp one swells, and nobody blew into anything.

Why It Moved

The pressure in the inflated balloon was higher than the pressure in the limp one. That difference is the whole cause. Air moves from a region where the pressure is high to one where it is lower, and it needs nothing else to push it.

Then It Stops

Watch a little longer and something just as useful happens: the flow stops, with both balloons at roughly the same size. The air kept moving only while one side was at a higher pressure. Once the two matched, there was nothing left to drive it.

Bigger Difference, Faster Flow

One more thing follows. If you could measure the speed of the air crossing the straw, you would find it higher when the difference in pressure is larger. A small difference gives a gentle flow and a large one gives a fierce one.

A Breeze Off the Sea

You met the sea breeze in Grade 7, and now it has an explanation. By day the land heats up faster than the water. The air above the land becomes warmer and lighter, so it rises, leaving a low pressure region behind it. Air from the higher pressure over the sea moves inland to take its place, and that is the sea breeze.

And One Off the Land

At night it runs the other way. The water now holds more warmth than the land, so the low pressure region forms above the sea instead, and air moves out from the land to fill it. That is the land breeze. Both are the same rule applied to whichever surface happens to be warmer.

Now the Odd Part

So far, so reasonable. The next result surprises most people, and it is the one that explains storm damage. What happens to the pressure where air is moving fast?

Blow Between Two Balloons

Hang two inflated balloons from a stick with a gap of a few centimetres between them. Blow steadily through the gap. The balloons do not fly apart. They swing towards each other, and blowing harder brings them together faster.

Fast Air, Lower Pressure

The reason is that the fast-moving air between them is at a reduced pressure. The ordinary air on the outside of each balloon is now at the higher pressure, and it pushes them inwards. So high-speed wind is accompanied by a drop in pressure.

Why Roofs Blow Off

That explains something that looks very strange when you see it. In a storm, the wind racing over a roof lowers the air pressure above it while the air inside the house stays at ordinary pressure. The roof is pushed upwards from below, which is why roofs lift off rather than being pushed sideways.

Why to Open the Windows

And it gives advice that sounds wrong until you know the reason. Leave doors and windows open in a storm with high winds. Then the wind moves through the house as well as over it, the pressure inside falls with the pressure above, and the difference across the roof is much reduced.

What To Carry Forward

Air moves from high pressure to low, faster when the difference is larger, and stops when the two are equal. Sea and land breezes are that rule following the sun. And fast-moving air is at a reduced pressure, which is why a roof is lifted from below in a gale and why the windows should be open.

Scenario:

A gale crosses a village overnight. One house loses its roof completely; the house beside it, whose owner left the windows and doors open, keeps its roof. A third family had sealed every opening with sacking and lost half their tiles. In the morning a visitor says the wind must have hit the first and third houses side on and missed the second. A pupil who has just studied this chapter points at the roofs rather than the walls, and asks what the wind was doing above them.

Analysis:

The visitor is describing a push from the side, which would damage walls before roofs. What the chapter gives is a lift from below: fast wind over a roof lowers the pressure above it while the air inside stays at ordinary pressure. The pupil is looking in the right place.

Activity:

Hang two balloons with a gap between them and blow through the gap, then blow harder and compare.

Title:

Try it at home: blow them together

Safety:

Blow across the gap rather than at a balloon, and keep faces clear in case one bursts.

What You Notice:

They swing towards each other, and harder blowing brings them together faster. The fast air between them is at a lower pressure, so the ordinary air outside pushes them in.

Two balloons joined by a straw exchange air with nobody blowing into either of them, which shows a pressure difference is all a wind needs.

Blowing between two hanging balloons brings them together rather than pushing them apart, because fast-moving air is at a reduced pressure.

A roof in a gale is lifted from below rather than pushed over from the side, which is why open doors and windows help to save it.

HIGH TO LOW, UNTIL LEVEL — Air flows while a difference lasts and stops when the two pressures match.

FAST AIR PRESSES LESS — The surprising half. Blow between two balloons and they come together rather than parting.

From a Breeze to a Storm

The last topic ended with a rule about rising warm air and rushing cooler air. Turn that rule up and you get the weather in this one: storms, thunder, lightning and the largest of them all, the cyclone. They are not four unrelated events. They are one engine at different sizes.

The Engine

Here it is. The ground warms, and the warm moist air above it is lighter, so it rises and leaves a region of low pressure behind. Cooler air from the higher pressure around rushes in to take its place. That air is heated in turn and rises too, and the cycle keeps running.

Clouds, Then Rain

As the rising air climbs it expands and cools, and the moisture in it turns into water droplets. Those droplets are what you see as cloud. They merge into heavier drops, which fall as rain, or as hail, or as snow.

What Makes a Storm

Strong winds together with that rain are what we call a storm. India is hot and humid over much of the year, which is exactly the condition storms need, so they are frequent here.

Up Where It Is Freezing

Sometimes the warm air rises so high that the temperature up there turns those water droplets into particles of ice. Now there are two kinds of thing in the cloud, water and ice, and strong winds are rushing both up and down through it.

Rubbing, Inside a Cloud

You know what happens when two things rub against each other, because you charged a balloon with a woollen cloth in the chapter on forces. In the cloud, water droplets and ice particles rub past each other in the same way and build up static electric charges.

Charges Sort Themselves Out

Then the charges separate, because the two carriers are not the same weight. The lighter positively charged ice particles are carried to the upper part of the cloud. The heavier negatively charged water droplets stay in the lower part. The cloud now has a top and a bottom with opposite charges.

And the Ground Joins In

When the negatively charged underside of the cloud comes close to the ground, it makes the ground and the things on it, trees and buildings, positively charged. Now there are opposite charges facing each other across a gap of air.

Air Gives Way

Ordinarily air is an insulator and keeps opposite charges apart. But if the charge keeps building, air loses its hold as an insulator. Charge then flows suddenly across, and the bright flash that makes is lightning. It is not only cloud to ground: the charges can meet inside one cloud, or across to a second cloud, or down to the earth. All three are lightning.

And the Sound

The flash heats the air around it extremely quickly. Hot air expands, and that sudden expansion is what you hear as thunder. So thunder does not cause lightning; it is the sound of lightning having happened. A storm with both is called a thunderstorm.

Local Names, Local Good

Some thunderstorms are local affairs with local names. West Bengal, Bihar and Jharkhand know them as Kalboishakhi, and Assam as Bordoisila. Both arrive before the monsoon and help the kharif crops along. Further south they are mango showers, named in Tamil Nadu, Kerala and Karnataka for the fruit they ripen, and in Karnataka the coffee plants gain too.

Staying Safe

Lightning is dangerous. It starts fires, damages buildings and kills or badly burns people and animals. So stay well clear of anything tall. Crouch in a low open area, keeping your contact with the ground as small as you can, and do not lie down flat. Leave an umbrella with a metal rod alone. Get out of water. A bus or a car is comparatively safe.

A Rod Down the Wall

Buildings can be protected during construction. A lightning conductor is a metal rod fixed along a wall, with a pointed end held higher than the highest part of the building and the other end buried deep in the ground. It gives the charge an easy path down into the earth.

The Largest Version

Now the big one. A cyclone forms over warm ocean water. The warm moist air above the sea rises, and as it rises the water vapour in it condenses into raindrops. Condensing releases the heat that evaporation took in, and that heat warms the rising air further, so it rises higher still and leaves a pressure even lower than before. Air rushes in from all around and rises too, and the spin of the Earth sets the whole moving mass turning.

The Eye

Repeat that cycle and you have a region of very low pressure with fast winds turning round it. That is a cyclone. At its centre is the eye, where the pressure is lowest and the wind is calm. Everything around the eye is anything but calm.

When It Reaches Land

A cyclone crossing from sea to land is cut off from the warm moist air that fed it, so it gradually loses strength. That is not the end of the matter. It leaves damage that takes months or years to repair, it drives a wall of seawater inland that floods coastal land, and its rain overflows rivers and triggers landslides. Seawater spoils drinking water and salts farmland, fallen trees block roads, and power can be out for days.

Watching and Warning

What makes the difference now is warning. The India Meteorological Department issues alerts, and satellites let a cyclone be tracked and its path predicted. If you live where cyclones come, keep an emergency kit ready and move to a designated cyclone shelter when one is coming.

What To Carry Forward

Warm air rises and leaves low pressure; cooler air rushes in. That makes clouds, rain and storms. Rubbing inside a tall cloud separates charge until the air gives way, which is lightning, and the air it heats makes thunder. Over a warm ocean the same engine builds a cyclone, with a calm eye and a violent ring, and what protects people is warning and shelter.

Scenario:

The India Meteorological Department tells a coastal town that a cyclone will make landfall overnight. Families move to the designated shelter, which is on higher ground a short walk from the market. Several hours of violent wind and rain are followed by a strange calm. Three families decide the storm has passed and set off home. Within half an hour the wind returns from the other direction, as strong as before. Afterwards the water supply tastes of salt. A nearby field will not grow its usual crop.

Analysis:

The calm was the eye, where the pressure is lowest and the wind drops away. The violent ring was still to come on the far side. The salt water and the ruined field are the second half of what a cyclone does. A surge of seawater driven inland contaminates drinking water and leaves soil less fertile.

Activity:

Find the last cyclone warning issued for your state and list what it told people to do.

Title:

Try it at home: make a lightning plan

Safety:

This is a planning exercise only. Never go outdoors to test anything during a storm.

What You Notice:

The plan is mostly about what to avoid rather than what to do. The open field is the hardest case. Go to a low open area, crouch down, keep as little contact with the ground as you can manage, and never lie flat.

The same rubbing that charges a balloon with a woollen cloth charges a storm cloud, with water droplets and ice particles rubbing past each other instead.

A lightning conductor does not keep charge away from a building; it offers the charge an easy path down into the ground.

Local pre-monsoon thunderstorms are welcomed by farmers, and are called mango showers in the south because they help the fruit ripen.

FLASH FIRST, SOUND AFTER — Lightning heats the air and the air expands. Thunder is the sound of that, never its cause.

THE EYE IS CALM, NOT SAFE — A lull in the middle of a cyclone means the far side of the ring is still to come.