Waves are generated way out at sea by the wind. Even a slight breeze can disrupt the surface of the water so that ripples and small waves form. The size of a wave depends on the weather conditions, currents and tides. Waves can travel for thousands of miles before they reach land.

For more information go to how stuff works

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When it rains on land, the water dissolves salts and minerals from soil and rock and this flows into streams, then rivers and finally the sea.

Water then evaporates from the sea leaving the salt behind and forming clouds that produce rain over the land. Over millions of years this circular process, called the water cycle, has resulted in fresh water streams but salty seawater.

Evaporates: Evaporation is when the sun heats up water in rivers or lakes or the ocean and turns it into vapour or steam

It’s maybe not just the Earth’s seas that are salty:

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Anything will float as long as its overall density is less than the fluid that it’s in. This means that even enormous cruise ships and oil tankers can float as long as they are less dense than water. To make sure this is the case, ships are designed so that they are not just solid lumps of metal, instead there are lots of empty spaces full of nothing but air inside a ship’s hull.

You can test this out for yourself with a lump of plasticine and a bowl of water. Roll the plasticine into a ball and see if it will float. Now shape the plasticine into a boat shape – it should float even though it’s the same amount of plasticine.

Density: Density is how heavy something is for its size

Hull: The watertight body of a ship

For more information go to the BBC Schools website

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Ice cubes are solid water. We’re used to liquid water from the tap because at room temperature water is a liquid. However, if you heat up water, for example in a kettle, you can change liquid water into a gas – steam. And if you cool it down, for example in a freezer, you can change liquid water into a solid – ice. Pure water freezes at 0 degrees centigrade.

In liquid water the molecules can move about quite easily which means that you can pour yourself a glass of water. But when you cool water down to its freezing point, the molecules don’t have enough energy to move about making ice a solid.

Molecules: Molecules are small particles made up of atoms, the building blocks of all living and non-living things

Have a go at lifting an ice cube with just a piece of cotton! Try 'Sew an ice cube' at physics.org

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Light travels much faster than sound which is why you see lightning before you hear thunder even though they happen at the same time. You can estimate how far away a thunderstorm is by counting the seconds between seeing a bolt of lightning and hearing the thunder. Sound travels about one mile every five seconds, so dividing the time by five gives you the distance you are from the storm in miles.

For more information got to: Lightning and Thunder at the UCAR website.

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The Sun doesn’t go anywhere at night time, but we can no longer see it at night because the Earth has moved. Every 24 hours, the Earth rotates on its axis. This means that as night falls and we see the Sun drop below the horizon all that is happening is that our side of the Earth is turning away from the Sun.

As night falls in the UK, for example, dawn is breaking in New Zealand on the other side of the Earth.

Earth’s axis: An imaginary line that extends from the North pole through the Earth to the South pole.

Horizon: The line at which the sky and earth appear to meet.

The sky’s more interesting at night. Take a look at popastro.com to see what you can see. 

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All stars are massive balls of extremely hot gas that give off energy. The pressure and heat are so great inside stars that atoms fuse together, releasing energy. The nearest star to the Earth is the Sun. We see and feel the energy that the Sun gives off as heat and light, but it also emits lots of other types of energy.

In the daytime, the Sun is the only star we can see as it is so bright it outshines all the others. But at night we can see a multitude of stars. You can tell the difference between a star and a planet in the nightsky because the light from a star changes in brightness whilst you’re watching – stars really do twinkle.

Fuse: Mix/blend

For more information about stars go to Science and Nature on the BBC website.

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It is too cold in winter for bees and many other insects to be active. Some bees that live in large groups called colonies, like honeybees, shiver during winter to keep warm. In winter the honeybee workers all huddle together around the queen bee in the centre of the hive where they vibrate their wings to generate warmth and so keep the rest of the bee colony warm too. During this time the bees live off the honey they made during the summer. In other bees like the bumblebee, all the male bees die at the onset of winter and only the queen bee survives to start a new colony the next spring.

For more information about bees go to the British Beekeepers Association website

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Tortoises have a shell to protect them against predators - a kind of ‘shield’. The tortoise shell is made from the animal’s ribs and backbones that are fused together and so it is a part of its body. Several plates that are made of the same material as our fingernails, (a protein called keratin), cover the surface of a tortoise’s shell.

Scientists have recently discovered how tortoises get their shells. Go to the BBC website to find out more.

Answer verified by Dr Richard Kirby, Royal Society University Research Fellow

In most animals like us, babies are created when a cell from the mother and a cell from the father join together or ‘fuse’. In humans, to make a baby you need to have sperm from the father and an egg from the mother. Each of these cells contains exactly half the information needed to make a baby. After the two cells fuse they divide over and over again to create a ball of cells called an embryo that goes on to become a baby that grows inside the mother until it is born 9 months later.

For more information about how to talk to your children about sex and relationships, see fpa’s Speakeasy website

Answer verified by Dr Richard Kirby, Royal Society University Research Fellow

The Sun produces white light which is made up of all the colours of the rainbow. But a clear cloudless day-time sky is blue because special things called molecules in the air scatter blue light from the sun more easily than they do red light. The blue light gets scattered in all directions so you can see blue whichever way you look. That’s why we have a blue sky.

To find out more about why the sky is blue go to NASA's Space Place website

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Light and water make a rainbow – with a little help from the sun! Light is made up of lots of colours (red, orange, yellow, green, blue, indigo and violet). When they are all mixed together they make a clear light – scientists call it ‘white light’. When white light passes through water or glass it can split into all the different colours that make up white light. We usually see a rainbow when it’s raining and the sun comes out. Even after it’s stopped raining, water droplets are floating in the air, so when the sun comes out and shines on them, the light splits up into colours and you see a rainbow.

Find out how to make your own ‘rainbow’ without getting wet take a look at reflecting rainbows

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Flowers and most plants grow by taking in food, water and energy. Flowers suck up water and food from the soil through their roots and they get energy from the sun shining on their leaves, like a solar panel.

To find out more about flowers go to the Kew Gardens website or visit The atmosphere, climate and environment information programme

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Isn’t it amazing that a massive lump of metal, with chairs, all our suitcases and us can fly through the air? They can because planes are carefully designed to cheat gravity. Passenger jets can weigh up to 400 tonnes so it’s a lot to lift into the air – but they are designed in a special way so that they can get off the ground and fly!

There are four forces that help a plane fly in the air – they are called lift, weight, drag and thrust. When the lift is greater than the weight of the plane it will fly. One explanation of how the plane’s wings create lift is that the air on the top of the wing is moving more quickly than the air underneath the wing. This difference in speed creates a difference in pressure and sucks the plane upwards.

The thrust is made by the plane’s engines and planes need it to overcome the drag (resistance) the air makes. When the thrust, moving the plane forwards, is the same as the drag, holding the plane back, the plane flies at a constant speed.

For more information about how planes fly go to how stuff works

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Grains of sand are tiny particles of rock that over time have been worn down by rain, frost and wind on land and also by the sea hitting against the rocks at the coast. Salt water also helps to make sand by dissolving minerals in the rock, weakening the rock’s structure which breaks it down into sand.

For more facts and information about sea life go to the BBC's Blue Planet site

Answer verified by Dr Richard Kirby, Royal Society University Research Fellow

Fish breathe underwater by using their gills – our lungs help us to breathe and gills are like lungs. Just like our lungs, a fish’s gills have a good blood supply and as the water flows over the gills the oxygen it contains is absorbed into the fish’s blood.

For more facts and information about sea life go to the BBC's Blue Planet site

Answer verified by Dr Richard Kirby, Royal Society University Research Fellow

The deepest part of the sea is about 10 kilometres deep. You couldn’t swim there because you would be squashed by the pressure of water above you, which is nearly 1,000 times the air pressure at the sea surface. Even Alvin, a deep-sea vehicle designed especially to cope with high pressures to help scientists to study the deep ocean, cannot visit the deepest parts of the sea.

For more facts and information about sea life go the the BBC's Blue Planet site

Answer verified by Dr Richard Kirby, Royal Society University Research Fellow

Air (oxygen) that you need to breathe gets into your body through your nose – but your nose is also a place where other things try to get in, like nasty germs that could make you ill. To stop these nasties getting into your body, your nose makes mucus – we call this mucus “bogeys” or “snot”! It’s a gunky mix of body liquids that traps dust, smoke, germs and anything else small enough to get up your nose. Have you noticed that if you’ve been somewhere really grimy your bogeys turn black?

For more information on the human body visit the Kids First for Health Body Tour website or visit the Me and My Body Gallery at the Eureka Centre, Halifax.

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You burp when too much gas gets into your stomach. This can happen for lots of reasons, like when you drink fizzy drinks too fast, talk while you are eating or eat too fast. The easiest way for the gas to escape from your stomach is back up through your mouth as a burp. If the gas stayed there it would be very uncomfortable. It makes a noise when you burp because when the gas passes through the pipe between your mouth and stomach (called your oesophagus) it makes the top of the pipe vibrate.

For more information on the human body visit the Kids First for Health Body Tour website or visit the Me and My Body Gallery at the Eureka Centre, Halifax.

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