Category Science

You don’t have to watch a covered saucepan to know when the food or water inside it is boiling. The lid will begin to bounce up and down when the water begins to boil. The push that moves the lid comes from steam.

As the water inside the saucepan is heated, the molecules take up energy. That energy makes the molecules speed up and push hard against one another. When the water is hot enough, some of it changes from a liquid to a gas called steam.

The molecules of gases move around more and are further apart than the molecules of liquids. So the steam expands. It takes up much more space than the hot water did. But there is only one place where the steam can escape – through the spaces around the saucepan lid. It squeezes out with a hard push, and the push bounces the lid up and down.

Steam also can be used to push the moving parts of machines—to run ships, trains, and factories that make electricity. Such big machines need very strong pushes from expanding steam. So huge amounts of water must be boiled.

Sometimes, in cool weather, the insides of our windows look cloudy. They are covered with a thin film of water. Where does this water come from?

It comes from water vapour, water molecules mixed with the air inside the house. The water collects on the windows when the glass is cool.

Water vapour is a gas. The molecules of water vapour are as warm as the air around them in the house, so they move very fast. But when the molecules hit the cool glass in the window, they lose heat. As the molecules grow cooler, they move closer together and slow down. When they are moving slowly enough, they condense, or turn into tiny drops of liquid water.

Sometimes when the weather is very cold, the glass in the windows gets much colder than the air inside the house. Then the molecules of water vapour lose even more heat when they touch the glass. They slow down much more and move much closer together. When they get close enough to pull hard on one another, they freeze. Then the window is covered with frost – thin, feathery bits of solid ice.

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Cold butter on hot toast doesn’t stay cold for very long. Some of the heat from the toast passes into the butter, and so the butter becomes warm, too. The heat is a form of energy. Heat energy can spread. Heat energy always flows from something warmer to something cooler. The movement of molecules passes the heat along.

A slice of toast is a solid piece of bread. But the molecules in the bread move. They wriggle and jiggle, even though they are held together. As the bread is toasted, the heat from the toaster makes the molecules speed up.

Cold butter is solid, too. But its molecules are moving very slowly. When you spread the cold butter onto the hot toast, some of the fast-moving toast molecules bump into the slow-moving butter molecules. That makes the butter molecules move faster. The jiggling motion moves from molecule to molecule until the butter is soft and warm.

Put five coins with different dates in a small box. Show them to some friends and explain that you will read your friends’ minds. While your back is turned, get your friends to choose one of the coins and remember its date. Ask each friend to hold the coin tightly in one hand for a moment and to concentrate on the date. When everyone has had a turn, ask the last person to drop the coin in the box. Turn around right away and touch each coin lightly. Four of the coins will be cool – but the fifth will be warm, because it has taken heat energy from your friends’ hands. Pick that coin, read the date, and amaze your friends!

Can you fry ice cubes? You can try, but if you heat ice cubes in a pan, they won’t be ice cubes anymore. The ice will melt into water. And after a while, the water will boil and turn into steam. What makes the ice cubes change?

Ice melts because something happens to its molecules. Heat energy makes the molecules move faster. As the molecules speed up, they begin to move away from another. Then the ice changes from a solid to a liquid – water.

Heat speeds up the molecules in liquids, too. So as the molecules speed up, they move even further apart. Finally, they lose almost all their pull on one another. Then the liquid evaporates. It becomes a gas.

And that’s what happens when water boils. Heat makes the molecules roll and tumble faster and faster in the pan. When the water molecules are moving fast enough, they become steam. The molecules of steam mix with other molecules in the air.

Picture Credit : Google

On a chilly day, you can rub your hands together to warm them. Why does rubbing your hands make them warm?

You are made up of molecules, just like all the other kinds of matter around you.

When you rub your hands together, you create friction. You make the molecules in your skin bump and push one another.

That makes the molecules speed up. It gives them more energy. The faster the molecules move, the warmer you get. So if you rub hard enough, your hands feel warm.

Biff! The racket hits the tennis ball, and the ball sails across the net. A point is scored – thanks to a hamburger!

Of course, the hamburger did not actually hit the ball. The player did. But the player ate the hamburger for lunch, and the player’s body got energy from the hamburger. Some of this energy was used to swing the racket. And the energy in the swinging racket knocked the ball over the net. So stand up and cheer for the hamburger. It helped score the point!

There are only a few kinds of energy. But each kind of energy can change into other kinds. Chemical energy in the food you eat can be changed into the energy of movement when you run or hit a ball.

Picture Credit : Google