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Try this: Teabag rocket

All you need is a saucer, a teabag and a match for this clever little trick.

Straighten the teabag out and open it up, so it forms a cylinder. The fire will burn down the cylinder.

As it nears the bottom, the teabag will lift up into the air and float towards the ceiling.

Up, up and away.

This is a classic experiment we thought you might not have seen. Once you've completed it you can claim to be a rocket scientist – very impressive!

You will need

• A teabag. Use one that is made from a tube that has been folded over and stapled at the top.
• A small plate or saucer (not plastic)
• Matches
• Water, fire blanket or extinguisher
• Adult

WARNING: This activity involves using matches and fire. For any activity involving fire, you must have an adult present, plus water and preferably a fire extinguisher and any other safety equipment the adult or yourself feels is needed. Only use fire in a safe place, away from flammable materials.

What to do

This activity works best indoors, with no drafts or air conditioning.

1. Remove the staple from the teabag.
2. Empty the tea out.
3. Straighten the teabag out and open it up, so it forms a cylinder.
4. Stand the cylinder on the plate.
5. With an adult present or helping, light the top of the cylinder.
6. The fire will burn down the cylinder. As it nears the bottom, the teabag will lift up into the air and float towards the ceiling.

What's happening?

As the fire burned, it heated up the air around it. When air heats up, it expands, so it becomes less dense. Since the hot air above the fire was less dense than the cool air around it, it started to rise up towards the ceiling.

As the hot air rose up, the cooler air around the teabag moved in to take its place. As the cooler air moves in, it is also heated up, so it also rises. The constant movement of air from heat causes a current in the air going up from around the end of the teabag, pushing the teabag higher and higher.

At first, the cylinder is too heavy for the current in the air to lift it. As it burns down, it becomes lighter, until it is light enough for the air current to pull it up into the air.

This sort of air current is called a convection current. Convection currents are currents caused by a fluid rising or sinking as it is heated or cooled. Convection currents happen in water or in air. They are one of the most efficient ways of spreading heat around.

The air currents around the cylinder.

Applications

Convection within Earth's mantle is the driving force for plate tectonics. There are actually two convection currents occurring within the Earth.

The first is the outer core, which is thought to be made of liquid iron. This is where the Earth's magnetic field is generated. Every few hundred thousand years, the magnetic field reverses, so Earth's magnetic poles (north and south) shift. Scientists know this by studying the magnetism preserved in rocks. Lavas and sedimentary rocks containing iron minerals lock in the direction of the magnetic field when they solidify.

As heat from the inner and outer core heat the lower portion of the mantle, a second set of convection currents form. This mantle convection is extremely slow, as the mantle is a thick semi-solid with the consistency of a very thick paste. This slow convection can take millions of years to complete one cycle.

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Article generously contributed by CSIRO

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