SPINNING PLANET

The earth is like a giant ball spinning in the darkness of Space. The only light falling on it is the light of the sun, glowing 93 million miles away. The earth turns once a day, and it orbits the sun once a year. The experiments on these pages investigate the two ways of moving, and explain why night and day, and the seasons, occur. The ball represents the earth and the flashlight, the sun. in the final project, you can make a simple thermometer using water to record changes in temperature from night to day, and from season to season.

NIGHT AND DAY

Felt-tipped pen, plastic ball, piece of thin string, non-hardening modeling material, flashlight.

STEP 1
Draw or stick a shape on the ball to represent your country. Stick the string to the ball with modeling material. Tie the string to a rail, such as towel rail, so that the ball hangs freely.

STEP 2
Shine the flashlight on the ball. If the country you live in is on the half of the ball in shadow on the far side, then it is night, because it is facing away from the sun.

STEP 3
Your home country may be on the half of the ball lit the flashlight instead. If so, it must be daytime here because it is facing the sun. Keep the torch level, aimed at the middle.

STEP 4
Turn the ball from left to right. As you turn the ball, your country will move from the light half to the dark half. You can see how the sun comes up and goes down as the Earth turns.

THE SEASONS

Felt-tipped pen, plastic ball, bowl just big enough for the ball to sit on, flashlight, books or a box to set the flashlight on.

STEP 1
Use the felt-tipped pen to draw a line around the middle of the ball. This represents the Equator. Sit the ball on top of the bowl, so that the equator line is sloping gently.

STEP 2
Put the flashlight on the books so that it shines just above the Equator. It is summer on the half of the ball above the Equator where the flashlight is shining, and winter on the other half of the world.

STEP 3
Shine the flashlight on the Equator. It sheds equal light in each half of the ball. This is the equivalent of spring and autumn, when days and nights are a similar length throughout the world.

MAKE A THERMOMETER

Water, bottle, food coloring, clear straw, reusable adhesive, card, scissors, felt-tipped pen.

STEP 1
Pour cold water into the bottle until it is about two-thirds full. Add some food coloring. Dip the straw into the water, and seal the neck tightly with reusable adhesive.

STEP 2
Blow down the straw to force some extra air into the bottle. After a few seconds, the extra air pressure inside will force the water level to rise up the straw.

STEP 3
Cut the card and slot it in over the straw. Let the bottle stand for a while. Make a mark on the card by the water level to show room temperature. Take your thermometer outside.

STEP 4
On a hot day, the sun’s heat will make the air and water expands, forcing the water level in the straw above the room temperature mark. Cool the thermometer in the fridge. Mark the different levels.