1. When we are on Earth, the planet exerts a force called gravity on us. This force means that everything on the planet has a tendency to fall towards the centre of the planet. Because our planet is solid, we can only fall as far as the surface!

It allows us to move about on our planet’s surface, to put things down and know that they won’t fly away by themselves, to put buildings on the ground and know that they won’t fly off. It makes water behave the way we are familiar with forming lakes, streams, rivers, seas and oceans. It keeps our atmosphere in place around our planet and allows life to flourish. It gives us a feeling of ‘weight’.

When astronauts go up into space, they experience ‘weightlessness’. Things no longer behave as they down on the surface - liquids float endlessly in spherical drops, you cannot push down on things to exert a force for example to lift something because you merely push yourself off the floor. Astronauts have to strap themselves in to sleep or to sit even and it is very hard to get worthwhile exercise because your muscles do not have anything to push against. Over a fairly short period of time in space, astronauts lose a significant amount of muscle and their bones lose calcium because they no longer have to support weight.

The actual explanation for weightlessness is not that the astronauts are beyond Earth’s gravitational pull but rather more complex (see Teacher’s Note below.)

A good way to approach this with the children is to ask them to draw their bedroom on Earth. Underneath they are to imagine that there is no gravity and redraw their bedroom with everything floating about. (Just when their parents couldn’t imagine anything more untidy!)

If you can find some video footage of space travel showing weightlessness it would give the children a much better idea.

If you have the internet then try the NASA kids page there are activities, trivia games etc for the children and a teachers section with lesson plans etc and photos and videos of weightlessness.

Astronauts in orbit are close enough to the Earth to experience some gravity but being in orbit means that they are falling towards the Earth. Because the spaceship and everything in it is all falling at the same rate they become weightless. This is like the feeling you get on high-tech rides - that moment when your stomach leaps - you are experiencing weightlessness for a second or two.

An interesting little investigation you can do which involves the weightlessness of free-fall only needs a styrofoam cup, some water and a washing- up bowl.

Punch a small hole in the side of the cup near the bottom.

Hold your thumb over the hole as you fill the cup with water.

Ask the children what will happen when you remove your thumb. Take your thumb away and let the water stream out into the bowl. Fill the cup again with your thumb over the hole.

Ask the children if the water would pour out if you drop the cup. Drop the cup into the basin from as great a height as possible. If you can get one of the children to video the fall then play it back in slow motion.

Because the cup and water are falling at the same rate and time, the water stays in the cup. They are both in free fall.

Most of the planets travel around the Sun in an elliptical path. Pluto has a more elongated orbit and from time to time is closer to the Sun than Neptune.

It was Nicholas Copernicus in the early 16th century, who put forward this theory. However, it was not until the end of the 17th century and the work of Isaac Newton on gravity that the movement of the planets was fully explained.

(The orbit of Mercury is irregular and was only explained in the 20th century by the work on relativity by Albert Einstein.)