TEA BAG
|
TEA BAG
|
| Subject Area |
Heating and cooling curves. |
| Age
or Grade |
Ninth grade physics (Ages 14-15 years old) |
| Estimated Length |
20 minutes |
| Prerequisite knowledge/skills |
Knowledge on heating by convection is useful. This demonstration can relate to why hot air rises and hot and cold temperature currents across the globe. |
| Description of New Content |
Fix misconceptions on why hot air rises. It is actually not the hot air rising, but the cool air coming to take its place. Hence, pushing the hot air up. This leads into a discussion on densities of gases. |
| Goals |
Students will understand convection and hot and cold air currents. |
| Materials Needed |
One empty tea bag. Lighter. |
| Procedure
|
Opener - Discuss hot and cold currents as seen on weather
maps.
Development - Ask students what they think will happen when the top of the bag is lit. Most say the flame will burn from top to bottom and the bag will disintegrate. Closure - Discuss what happened as it relates to physics.
|
| Evaluation |
Asking open ended questions after demonstration. |
| Extensions |
Can relate back when discussing the 3 types of heating,
convection, conduction, and radiation. Air currents generated by heat are
called convection currents. Convection currents form because of the
difference in density between hot and cold air. As the air around a heat
source increases in temperature, its density decreases (it gets lighter) and
it rises, creating an updraft. In this demo, the convection current
generated by heat from the burning tea bag creates an updraft. The updraft
is what causes the bag to lift off the bench top. |
| References | Keith Magni http://www.carolina.com/chemistry/experiments/teabag.asp |