Water is essential for life on Earth and many scientists believe that if other planets are able to support life then they too must have water!


We all know what it looks like! It appears to us as a transparent, colourless, odourless liquid. The sea, a lake or river may look green/blue but this is due to the many ‘salts’ dissolved in it as well as reflections from the seabed and the sky.



Water doesn’t really have a shape of its own. It takes the shape of whichever container we put it in. These three containers are different shapes and the water in them can have vertical sides, sloped sides or curved sides.



The top surface of the water in any container, even a whole swimming pool is always flat and horizontal as long as the water is allowed to settle eg. on calm day.



Water can ‘flow’. This means it can form a continuous moving stream. It can just hold itself together strongly enough to remain as one ‘body’ of material as it moves along when we pour it or when a river flows.

Flow in a tube

A ‘fluid’ is the name given to materials which can flow in pipes. Water is a fluid and so is oil or thick sticky treacle. Water can flow very quickly through a pipe and this is very useful! Gases such as Oxygen can flow in pipes so they are also members of the ‘fluids’ family!



All materials weigh something! If we measure out exactly 1 litre of water and place it on some weighing scales we find that its mass is 1 Kg. Water is really quite heavy compared to other materials of the same size (volume). The same volume of wood weighs less than 1 Kg!

Gravity affects water!

Gravity is amazing! It is something we all experience but find difficult to understand. We believe that gravity is responsible for the force which is pulling us down onto the planet Earth and stopping us from floating off into space. The very large mass of the Earth results in a large force due to gravity pulling us towards it. The force of gravity is exerted on all objects or materials including water and air.
This explains why water has some of the characteristics described above.
Water is being pulled down towards the Earth. Every little part (molecule) of the water is being pulled the same so when it is allowed to settle it forms a flat, horizontal surface.
We said that water is a fluid and it can flow when we pour it, or when it is in a river or pipe. It is gravity which makes it flow down towards the Earth!

Water in our homes


We’re so used to having fresh water that we forget about the complex systems of pipes, reservoirs, pumping stations and purification equipment needed to maintain it!

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Fresh water reservoirs are nearly always high up in the mountains so that gravity can make the water flow down pipes to the waterworks and then to our homes. People who live high up above the level of water in a reservoir have to have their water pumped up the hill from the waterworks.
Most houses have a water tanks in the loft (in the roof space above your head) so that gravity can make the water flow down to the taps, shower and toilet.

The Water Cycle

This is one of the most important natural processes on the planet Earth. Without it life on Earth would not exist! The cycle shown below in picture form is much simplified and there are other processes taking place on Earth which also have an affect.

You can begin with any picture in the cycle and work your way round in a complete circle back to where you started.

water cycle in pics

Some things to think about

  1. What if our Sun wasn’t as hot as it is?
  2. What if too much pollution entered the skies and partially blocked the Sun?
  3. What if our Sun was much hotter?

Some odd things about water

Is the surface of water completely flat and horizontal? Most of the time it is correct to say ‘yes’, however, there are two common examples of when this is not true!

Water in a narrow tube

If you look very closely at the water level in a narrow glass tube you will see that it has a curved surface. It seems to ‘creep’ up at the edges as if trying to stick to the glass. This curved surface is called the ‘meniscus’ (Greek word for ‘crescent shape’). The reason for this is that the molecules of water on the surface behave differently from those in the main body of the water. They act like a stretched skin trying to hold the water in shape. The skin is affected by other objects in contact with it. Glass has the affect of attracting the skin and pulling on it. It pulls so much that it makes the water creep up the glass a little at the edges.

Water on the horizon out at sea

If you are at the seaside or out at sea on a ship and you can see a very wide view of the horizon you will notice that it is not flat but curved down at the left and right hand sides. This is because you are looking at the curved surface of the Earth. Of course this is gravity at work again pulling the water downwards towards the centre of the Earth and in doing so spreading it out evenly around the surface of the planet (winds, waves and tides make the surface irregular of course, but overall the sea is reasonable level).


Water experiments and demonstrations

Water level in shaped containers

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Gather together a variety of different containers suitable for water - they don’t have to be cups! Plastic containers are best! Half fill each one. Describe the shape of the water in the containers eg. the water in the drinking glass top left is ‘cylinder shaped’. The water in the flower vase above is ‘spheroidal’ (great word!) - or possibly a ‘truncated spheroid’ - this simply means that it is based on a shape like a sphere or ball which has no edges, only curved surfaces, apart from the horizontal surface on the top in this case.
The container gives the water its shape and gravity causes the top surface to be horizontal.

Try estimating which container is holding the most water - remember you should only have them half filled. This is quite difficult because the shapes are different. How can you prove which amount of water is the greatest? How can we compare and measure different amounts  (Volumes) of water?

Water levels in a ‘U’ tube


You will need a piece of clear plastic tubing about 40cm long for this experiment.

Half fill the tube with water! This can be tricky because air bubbles can get trapped in the tube. If you have a tray of water then you can keep one end of the tube out of the water and submerge most of the rest of the tube. Water flows into the part of the tube which is submerged. Then remove the whole tube from the water and hold it in the shape of a letter ‘U’ as in the picture.

You should notice that the water levels settle down to be the same providing you don’t keep moving the tube about.

The reason why the water level is the same in both sides of the tube is that gravity is acting equally on the water just like two people of exactly the same weight on a see-saw.

Try raising one side of the tube a few cm higher than the other and watch what happens. Don’t lift too high or the water will overflow at the other end!

The tube in the pictures below has been improved by adding an open syringe tube on each end. This makes it easier to see what is going on - especially if you use coloured water! Using wooden stands means that you don’t have to hold it all the time.


Tubes allowed to settle. Both levels are the same and perfectly horizontal.


Right hand (RH) tube raised up then allowed to settle. Both levels are the same and perfectly horizontal.

Gravity acts on the whole mass of the water pulling it down towards the ground. The water in both sides of the tube is part of the whole body of water so gravity acts on it so as to create a level surface just like in a pond. The fact that the two halves are connected simply means that water can flow one way or the other so as to balance the effect of gravity.

Continuous water flow


At first glance this picture seems odd! The LH tube is raised up and the level in it is higher than the RH tube. This is because the picture was taken before the liquid has had a chance to settle under the effect of gravity - the liquid is still flowing from LH to RH.


Both levels are the same again now that the liquid has had the chance to settle.

Gravity has done the trick again!

Click the picture above for video clip.

This experiment is great fun and helps explain how water circulates in our houses.
Place one end of a tube into a container of water. Why doesn’t the water flow out from the other end? If the tube is clean you may wish to encourage the water to flow by sucking at the open end! This removes air from the tube and it is replaced by water - alternatively a syringe or pipette can be used to do this. Now place the free end into an empty container. The water may start flowing but you can speed it up by raising the full container higher up as in the third picture. You may have to try this several times to get it to work properly. The most common mistake is to let the end of the tube come out of the water and this lets air in which stops the flow. The right hand picture shows the water flowing - look closely - and filling up what was the empty container.

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We have created a water syphon which will continue to flow until......? When will the water stop flowing from the full jar into the other jar? Think about the ‘U’ tube experiment above!

The picture on the right shows a simplified version of the syphon. The water flows downhill due to the pull of gravity. No matter how long and coiled the tube is, the water will flow providing the tube has more ‘downhill’ than ‘uphill’ overall.

How could you reverse the syphon so that the left hand container can start to empty into the right hand container?


At home there are water storage tanks placed high up in the roof space to provide water by the flow of gravity. These tanks are kept ‘topped up’ because water from the water pumping station is continuously available to fill them when needed.

In this picture you can see the water tank in the loft and you can see the bath, toilet and washbasins with pipes leading to them.


Height of water - pressure


Floating on water

Water powered inventions


Swing bridge


High speed turbine

Roasting spit

Tube attached to funnel


Electricity generation

Electric lights at Cragside

enclosed waterwheel Armstrong
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