Science Projects And Inventions

YOU NEED –

• Two cardboard disks about 3’’ (7.5 cm)
• An empty wooden spool
• Some string

Cut out the disks from a cardboard. Use glue to stick them to the ends of an empty wooden spool. Take the string and wrap some around the spool.

Now pull the free end as in the illustration.

The question is will the spool roll away? Come towards you or will it stay where it is?

The answer is the spool will roll towards the person pulling it.

HOW DOES IT WORK?

A tug on the string it would seem will make the spool roll away from you.

But that is impossible because you are actually pulling it towards you.

No resistance is offered by the larger discs as a result of which the spool rolls towards you, while the string keeps winding around the spool.

The same phenomenon is true for a bicycle. Let somebody steady the bicycle. Move it till one pedal is directly below the other. Now tie a rope to the pedal at the bottom.

If you happen to stand behind the bicycle and tug on the rope, the bicycle will move forward.

However, the bicycle will actually roll backwards, for the same reason as the spool does.

FOOD FOR THOUGHT

What is a Chemical change? When a candle burns, the wax goes off in the air. This is because the chemicals in the candle are transformed into other chemicals and the dissipated into the atmosphere. This is called a chemical change.