Some Scientific Principles

Archimedes' Principle

Have you heard of Archimides' principle? It says: "Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object." Maybe it is a little difficult for you to understand. Let's try it with this funny demostration by the physicist Paul Hewitt.

Did you get it? I am pretty sure that you did and you are ready to do both activities below.

Think about it

Explain this picture in your own words.

Looking for information

Did you know that Archimedes figured out his principle thanks to a tricky question that tyrant Hieron had proposed to him? Look for information and write in your own words the whole anecdote. This picture will give you a hint.

Erasthostenes' measurement of the earth's circumference

What an amazing guy Erathostenes was! He measured the earth's circumference just by travelling from Syene to Alexandria in Egypt. Would you like to know how? Look at this video and then complete the cloze exercise below.

Now it's your turn

While visiting the city of Syene one day, Erathostenes noticed that the of the sun could be seen in the of a deep well. The sun was and the rays pointed to the of the earth. He remembered this and in the next mid-summer's day, in Alexandria, he the shadow cast by an . Sunbeams travel in lines so the difference in had to result from the of the earth.
If the angle was one-fiftieth of the , then the distance around the world must be times the distance from Alexandria to Syene. With these simple , Erathostenes made this almost exact measurement of the world more than hundred years before Magellan around it.

Key:
While visiting the city of Syene one mid-summer's day, Erathostenes noticed that the reflection of the sun could be seen in the bottom of a deep well. The sun was overhead and the rays pointed to the centre of the earth. He remembered this and in the next mid-summer's day, in Alexandria, he measured the shadow cast by an obelisk . Sunbeams travel in parallel lines so the difference in angle had to result from the curvature of the earth.
If the angle was one-fiftieth of the circle, then the distance around the world must be fifty times the distance from Alexandria to Syene. With these simple tools, Erathostenes made this almost exact measurement of the world more than seventeen hundred years before Magellan sailed around it.

Feedback:
While visiting the city of Syene one mid-summer's day, Erathostenes noticed that the reflection of the sun could be seen in the bottom of a deep well. The sun was overhead and the rays pointed to the centre of the earth. He remembered this and in the next mid-summer's day, in Alexandria, he measured the shadow cast by an obelisk . Sunbeams travel in parallel lines so the difference in angle had to result from the curvature of the earth.
If the angle was one-fiftieth of the circle, then the distance around the world must be fifty times the distance from Alexandria to Syene. With these simple tools, Erathostenes made this almost exact measurement of the world more than seventeen hundred years before Magellan sailed around it.

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