Activity: Teabag rocket
This is a nice activity that I have seen done as an after-dinner trick at a restaurant or café.
 |
|
Turn your teabag into a cylinder. |
 |
|
Stand it on your plate and light the top. |
 |
|
When it has burned down enough, the cylinder will be pulled up into the air. |
You will need
- A teabag. Use one that is made from a tube that has been folded over and stapled at the top. I found ones made by Liptons or Twinnings worked well.
- A small plate or saucer
- Matches
- Water
- Fire Extinguisher
- Adult
WARNING: This activity involves using matches and fire. For any activity involving fire, you must have an adult present, plus water, a fire extinguisher and any other safety equipment the adult or yourself feels is needed. Take care that you only use fire in a safe place.
What to do
This activity works best indoors, with no drafts or air conditioning.
- Remove the staple from the teabag.
- Empty the tea out.
- Straighten the teabag out and open it up, so it forms a cylinder.
- Stand the cylinder on the plate.
- Light the top of the 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.
What's happening?
As the fire burned, it heated up the air around it. As we have seen in previous activities, when air heats up, it expands, so it becomes less dense. Since the hot air around 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.
 |
|
The air currents around the cylinder. |
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.
Related activities
Warm air rising www.csiro.au/helix/sciencemail/activities/AirWeight.html
Convection in water www.csiro.au/helix/sciencemail/activities/Convection.html
Applications
- Convection currents give the flame of a candle and other fires their leaf-like shape. Candles and other fires rely on convection currents to supply them with a constant supply of oxygen. In freefall there are no convection currents (because there is no up or down) so flames behave very differently. You can see some examples of how fire burns without convection currents at science.nasa.gov/headlines/y2003/31jan_kelley.htm and science.nasa.gov/headlines/y2002/21aug_flameballs.htm
|
The Australian Greenhouse Office and mecu are proud partners of Science by Email.
|
|||
 |
 |
||
Science by Email is produced by CSIRO Education |
|||
