Galileo was the first thinker who tested his ideas by experimenting. He established the scientific process that we understand today of hypothesis (something we think is probably true), testing, observing, recording the observations and drawing conclusions based on what is seen. Here are some experiments you can do with your class about some of the things that interested Galileo.

 Floating things

Why does ice float? Put some ice in water. What would you expect to happen? What does happen? Push it under water and let go what happens? Why?

If metal usually sinks in water why do steel boats float?
Does wood always float? (Try with some very waterlogged rotten wood.)

Try with a selection of objects, which ones float? What do they have in common? Try with pieces of tin foil shaped as a sheet, as a ball, shaped like a shallow tray.

Float a needle on some water; what would you expect to happen? What does happen? Why?

Float two match sticks on water near each other, what happens? Why do they move together?



Galileo also did lots of work studying the motion of pendulums and he designed the first pendulum clock.

You will need at least a metre of string and different size weights to make a pendulum and a watch or clock that can time seconds

How many swings does the pendulum make in ten seconds? What would you expect to happen if you shorten the string by half or by a quarter? Try it: What would you expect if you put a heavier or a lighter weight on the end?  Write up your results in a table or graph.

Find or mark a straight line on the floor. Set the pendulum swinging along this line. Hold the end of the string as still as you can and take side steps slowly in a circle around it (as if your hand holding the string were at the centre of the circle). What would you expect to happen to the direction of the swing? What does happen to the swing of the pendulum?

The pendulum swings in relation to gravity not the person holding it so it should continue to swing along the line. This is an effect discovered by the French scientist Jean Bernard Leon Foucault.

Foucault set up a pendulum and left it swinging. It deviated from its original line over time because the Earth rotates. One set up at the North Pole would return to its original line in twenty four hours. This is one of the few experiments that you can do to prove the Earth’s rotation without leaving the planet.


 Watch the Moon

Galileo spent many, hours observing the sky to make his predictions about the Earth, Sun and Moon. Why don’t you have a go at studying the night time sky to see what you notice about the moon?

Look carefully at the moon and draw or photograph its appearance every night for at least two weeks (four weeks would be better).

Think about what shape and size it is. Write the day, date and time beside each sketch. (Ideally observations should be at the same time of night and from the same place) Can you explain why the Moon appears to change shape?

Collect all your drawings together and then compile a chart showing how the moon changes.

If you make an astrolabe (see activity) you can plot its rise and fall by measuring the angle above the horizon. You could plot this on a graph with time/date along the horizontal and the angle on the vertical axis.

You could show this for one night or for a month.

What would your results be like if you did the same measurements at a different time of year?

Can you answer these questions by experimenting?

To help you answer these questions you might like some simple things to help you like: balls of different sizes and colours, torches, cocktail sticks.


How long does it take for the Earth to spin once?
Shine a torch onto a slowly turning ball. what do you notice about the bit in shadow? What if you were to stand at one spot on the ball (mark it with a cocktail stick) What would change?

 Year & Seasons

How long does it take for the Earth to travel around the Sun? Shine a torch onto a slowly turning ball and move the ball slowly around the torch. Keep the torch pointing at the ball. What if the axis of spin is not North/South but East/West? What if it is somewhere between the two? What if the North Pole is not always away from the sun? (The Earth wobbles on its axis like a spinning top about to fall)

 Phases of the Moon & Eclipses

How long does it take for the Moon to travel around the Earth? Shine a torch onto a slowly turning ball, take another smaller ball and move this around the first. What do you notice about the light falling on the second ball? What would it look like if you were standing at one spot on the bigger ball? What happens when the small ball gets between the light and the bigger ball? What would this look like if you were standing on the bigger ball?

Your practical experiments may help you think abut these questions too:

  • Why do we get leap years?
  • What would happen to the seasons, plants and animals if the Earth took twice as long to travel around the Sun? How long would a year be?
  • Where would the Sun rise and set if the Earth went clockwise around the Sun instead of anti clockwise?
  • What would it be like on Earth if it didn’t spin?
  • What would it be like on Earth if it didn’t orbit the Sun?
  • Why do some parts of the Earth have long nights in winter and long days in summer?
  • Why is the day length almost constant at the equator?


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